From 103ea9d3f3a0d85a0d7c1ad98fd8dbb422505d95 Mon Sep 17 00:00:00 2001
From: wyv <wyv@google.com>
Date: Thu, 9 Dec 2021 04:52:37 -0800
Subject: [PATCH] Remove the concept of a "default" repo name and consolidate
 label parsing logic

This CL started as an effort to clean up references to RepositoryName.DEFAULT. This constant signifies that a label starts without a `@repo` part, and so usually refers to the "current repo". A Label or PackageIdentifier with such a repo name is unusable. This constant is really only ever meaningfully used *while* parsing a label to be relative from another one (Label#getRelativeWithMapping). So we remove it.

This also necessarily meant that we have to clean up the label parsing logic. There are multiple places in the Label, PackageIdentifier, and LabelValidator classes where the raw label string is parsed in some way and often they call each other, making the code nigh impossible to follow. This CL consolidates all the label parsing logic into one class, LabelParser, and makes all Label factory methods use this parser instead of their own logic.

PiperOrigin-RevId: 415235412
---
 .../lib/analysis/DependencyResolver.java      |   4 +-
 .../analysis/config/OutputDirectories.java    |   2 +-
 .../starlark/StarlarkRuleClassFunctions.java  |   1 -
 .../build/lib/buildtool/SymlinkForest.java    |   2 +-
 .../google/devtools/build/lib/cmdline/BUILD   |   1 +
 .../devtools/build/lib/cmdline/Label.java     | 308 ++++++------------
 .../build/lib/cmdline/LabelParser.java        | 195 +++++++++++
 .../build/lib/cmdline/PackageIdentifier.java  |  81 ++---
 .../build/lib/cmdline/RepositoryMapping.java  |   8 +-
 .../build/lib/cmdline/RepositoryName.java     |  25 +-
 .../build/lib/cmdline/TargetPattern.java      |   2 -
 .../lib/packages/AbstractAttributeMapper.java |   3 +-
 .../build/lib/packages/AspectDefinition.java  |  10 +-
 .../build/lib/packages/BuildType.java         |   3 +-
 .../packages/ConfiguredAttributeMapper.java   |   3 +-
 .../packages/PackageGroupsRuleVisibility.java |   8 +-
 .../lib/packages/PackageSpecification.java    |   2 +-
 .../build/lib/pkgcache/PackageOptions.java    |   8 +-
 .../lib/pkgcache/PathPackageLocator.java      |   2 -
 .../lib/rules/cpp/CcCompilationHelper.java    |   3 +-
 .../rules/java/JavaCompileActionBuilder.java  |   2 +-
 .../java/JavaHeaderCompileActionBuilder.java  |   2 +-
 .../build/lib/rules/java/JavaRuntime.java     |   2 +-
 .../java/OneVersionCheckActionBuilder.java    |   2 +-
 .../rules/repository/RepositoryFunction.java  |   8 -
 .../build/lib/skyframe/BzlLoadFunction.java   |   2 -
 .../skyframe/ConfiguredTargetFunction.java    |   4 +-
 .../ContainingPackageLookupValue.java         |   3 +-
 .../build/lib/skyframe/PackageFunction.java   |   3 -
 .../lib/skyframe/PackageLookupValue.java      |   1 -
 .../build/lib/skyframe/PackageValue.java      |   1 -
 .../lib/skyframe/ProcessPackageDirectory.java |   2 +-
 .../build/lib/skyframe/RecursivePkgKey.java   |   1 -
 .../build/lib/skyframe/SkyframeExecutor.java  |   2 -
 .../lib/skyframe/TransitiveTargetKey.java     |   1 -
 .../skyframe/TransitiveTraversalValue.java    |   1 -
 .../FakeStarlarkRuleFunctionsApi.java         |   1 -
 .../analysis/test/TestActionBuilderTest.java  |  22 +-
 .../lib/analysis/util/BuildViewTestCase.java  |   4 +-
 .../devtools/build/lib/cmdline/LabelTest.java |  18 +-
 .../build/lib/cmdline/RepositoryNameTest.java |   3 +-
 .../lib/pkgcache/LoadingPhaseRunnerTest.java  |   3 +-
 .../query2/testutil/AbstractQueryTest.java    |  11 +-
 .../lib/rules/LabelBuildSettingTest.java      |   2 +-
 .../RepositoryNameCodecTest.java              |   1 -
 .../StarlarkRuleClassFunctionsTest.java       |   7 +-
 .../build/lib/testutil/BlazeTestUtils.java    |  12 -
 47 files changed, 386 insertions(+), 406 deletions(-)
 create mode 100644 src/main/java/com/google/devtools/build/lib/cmdline/LabelParser.java

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/DependencyResolver.java b/src/main/java/com/google/devtools/build/lib/analysis/DependencyResolver.java
index ec29773f021083..74c11be759af58 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/DependencyResolver.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/DependencyResolver.java
@@ -679,10 +679,8 @@ private <T> void resolveAttribute(
       return;
     }
 
-    Label ruleLabel = rule.getLabel();
     type.visitLabels(
-        (depLabel, ctx) ->
-            outgoingLabels.put(dependencyKind, ruleLabel.resolveRepositoryRelative(depLabel)),
+        (depLabel, ctx) -> outgoingLabels.put(dependencyKind, depLabel),
         attributeValue,
         /*context=*/ null);
   }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/OutputDirectories.java b/src/main/java/com/google/devtools/build/lib/analysis/config/OutputDirectories.java
index 58dd68d9221048..a245cb361c1e88 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/OutputDirectories.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/OutputDirectories.java
@@ -256,7 +256,7 @@ private ArtifactRoot buildDerivedRoot(
     // instead. However, it requires individually symlinking the top-level elements of external
     // repositories, which is blocked by a Windows symlink issue #8704.
     RootType rootType;
-    if (repository.isMain() || repository.isDefault()) {
+    if (repository.isMain()) {
       rootType = isMiddleman ? RootType.SiblingMainMiddleman : RootType.SiblingMainOutput;
     } else {
       rootType = isMiddleman ? RootType.SiblingExternalMiddleman : RootType.SiblingExternalOutput;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
index b98c164704e9da..14ce51ea507038 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
@@ -130,7 +130,6 @@ public Label load(String from) throws Exception {
                   try {
                     return Label.parseAbsolute(
                         from,
-                        /* defaultToMain=*/ false,
                         /* repositoryMapping= */ ImmutableMap.of());
                   } catch (LabelSyntaxException e) {
                     throw new Exception(from);
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
index f8ece0f13526de..9a70756ce107d2 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
@@ -364,7 +364,7 @@ public ImmutableList<Path> plantSymlinkForest() throws IOException, AbruptExitEx
         continue;
       }
       RepositoryName repository = pkgId.getRepository();
-      if (repository.isMain() || repository.isDefault()) {
+      if (repository.isMain()) {
         // Record main repo packages.
         packageRootsForMainRepo.put(entry.getKey(), entry.getValue());
 
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/BUILD b/src/main/java/com/google/devtools/build/lib/cmdline/BUILD
index 21a2e040ddebf0..1acdae6fbc5ad3 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/BUILD
@@ -55,6 +55,7 @@ java_library(
     name = "cmdline-primitives",
     srcs = [
         "LabelConstants.java",
+        "LabelParser.java",
         "LabelSyntaxException.java",
         "PackageIdentifier.java",
         "RepositoryMapping.java",
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
index d5295952c6bada..d592862f65e937 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
@@ -13,20 +13,20 @@
 // limitations under the License.
 package com.google.devtools.build.lib.cmdline;
 
+import static com.google.devtools.build.lib.cmdline.LabelParser.validateAndProcessTargetName;
+
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ComparisonChain;
 import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Interner;
 import com.google.devtools.build.docgen.annot.DocCategory;
 import com.google.devtools.build.lib.actions.CommandLineItem;
-import com.google.devtools.build.lib.cmdline.LabelValidator.BadLabelException;
+import com.google.devtools.build.lib.cmdline.LabelParser.Parts;
 import com.google.devtools.build.lib.concurrent.BlazeInterners;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.packages.semantics.BuildLanguageOptions;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
-import com.google.devtools.build.lib.util.StringUtilities;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.skyframe.SkyFunctionName;
 import com.google.devtools.build.skyframe.SkyKey;
@@ -61,58 +61,74 @@ public final class Label implements Comparable<Label>, StarlarkValue, SkyKey, Co
   private static final String PKG_VISIBILITY_NAME = "__pkg__";
   private static final String SUBPACKAGES_VISIBILITY_NAME = "__subpackages__";
 
-  /**
-   * Package names that aren't made relative to the current repository because they mean special
-   * things to Bazel.
-   */
-  private static final ImmutableSet<PathFragment> ABSOLUTE_PACKAGE_NAMES =
-      ImmutableSet.of(
-          // Used for select
-          PathFragment.create("conditions"),
-          // Visibility is labels aren't actually targets
-          PathFragment.create("visibility"),
-          // There is only one //external package
-          LabelConstants.EXTERNAL_PACKAGE_NAME);
-
   public static final SkyFunctionName TRANSITIVE_TRAVERSAL =
       SkyFunctionName.createHermetic("TRANSITIVE_TRAVERSAL");
 
   private static final Interner<Label> LABEL_INTERNER = BlazeInterners.newWeakInterner();
 
+  // TODO(b/200024947): Make this public.
   /**
-   * Factory for Labels from absolute string form. e.g.
-   *
-   * <pre>
-   * //foo/bar
-   * //foo/bar:quux
-   * {@literal @}foo
-   * {@literal @}foo//bar
-   * {@literal @}foo//bar:baz
-   * </pre>
-   *
-   * <p>Treats labels in the default repository as being in the main repository instead.
-   *
-   * <p>Labels that begin with a repository name may have the repository name remapped to a
-   * different name if it appears in {@code repositoryMapping}. This happens if the current
-   * repository being evaluated is external to the main repository and the main repository set the
-   * {@code repo_mapping} attribute when declaring this repository.
-   *
-   * @param absName label-like string to be parsed
-   * @param repositoryMapping map of repository names from the local name found in the current
-   *     repository to the global name declared in the main repository
+   * Parses a raw label string that contains the canonical form of a label. It must be of the form
+   * {@code [@repo]//foo/bar[:quux]}. If the {@code @repo} part is present, it must be a canonical
+   * repo name, otherwise the label will be assumed to be in the main repo.
    */
-  public static Label parseAbsolute(String absName, RepositoryMapping repositoryMapping)
+  private static Label parseCanonical(String raw) throws LabelSyntaxException {
+    Parts parts = Parts.parse(raw);
+    parts.checkPkgIsAbsolute();
+    RepositoryName repoName =
+        parts.repo == null
+            ? RepositoryName.MAIN
+            : RepositoryName.createFromValidStrippedName(parts.repo);
+    return createUnvalidated(
+        PackageIdentifier.create(repoName, PathFragment.create(parts.pkg)), parts.target);
+  }
+
+  // TODO(b/200024947): Make this public.
+  /**
+   * Parses a raw label string within the context of a current repo. It must be of the form {@code
+   * [@repo]//foo/bar[:quux]}. If the {@code @repo} part is present, it will undergo {@code
+   * repoMapping}, otherwise the label will be assumed to be in {@code currentRepo}.
+   */
+  private static Label parseWithRepoContext(
+      String raw, RepositoryName currentRepo, RepositoryMapping repoMapping)
       throws LabelSyntaxException {
-    return parseAbsolute(absName, /*defaultToMain=*/ true, repositoryMapping);
-  }
-
-  public static Label parseAbsolute(
-      String absName, ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
+    Parts parts = Parts.parse(raw);
+    parts.checkPkgIsAbsolute();
+    // TODO(b/200024947): Make repo mapping take a string and return a RepositoryName.
+    RepositoryName repoName =
+        parts.repo == null
+            ? currentRepo
+            : repoMapping.get(RepositoryName.createFromValidStrippedName(parts.repo));
+    return createUnvalidated(
+        PackageIdentifier.create(repoName, PathFragment.create(parts.pkg)), parts.target);
+  }
+
+  // TODO(b/200024947): Make this public.
+  /**
+   * Parses a raw label string within the context of a current package. It can be of a
+   * package-relative form ({@code :quux}). Otherwise, it must be of the form {@code
+   * [@repo]//foo/bar[:quux]}. If the {@code @repo} part is present, it will undergo {@code
+   * repoMapping}, otherwise the label will be assumed to be in the repo of {@code
+   * packageIdentifier}.
+   */
+  private static Label parseWithPackageContext(
+      String raw, PackageIdentifier packageIdentifier, RepositoryMapping repoMapping)
       throws LabelSyntaxException {
-    return parseAbsolute(
-        absName,
-        /*defaultToMain=*/ true,
-        RepositoryMapping.createAllowingFallback(repositoryMapping));
+    Parts parts = Parts.parse(raw);
+    // pkg is either absolute or empty
+    if (!parts.pkg.isEmpty()) {
+      parts.checkPkgIsAbsolute();
+    }
+    // TODO(b/200024947): Make repo mapping take a string and return a RepositoryName.
+    RepositoryName repoName =
+        parts.repo == null
+            ? packageIdentifier.getRepository()
+            : repoMapping.get(RepositoryName.createFromValidStrippedName(parts.repo));
+    PathFragment pkgFragment =
+        parts.pkgIsAbsolute
+            ? PathFragment.create(parts.pkg)
+            : packageIdentifier.getPackageFragment();
+    return createUnvalidated(PackageIdentifier.create(repoName, pkgFragment), parts.target);
   }
 
   /**
@@ -126,56 +142,27 @@ public static Label parseAbsolute(
    * {@literal @}foo//bar:baz
    * </pre>
    *
-   * <p>Labels that begin with a repository name may have the repository name remapped to a
-   * different name if it appears in {@code repositoryMapping}. This happens if the current
-   * repository being evaluated is external to the main repository and the main repository set the
-   * {@code repo_mapping} attribute when declaring this repository.
+   * <p>Labels that don't begin with a repository name are considered to be in the main repository,
+   * so for instance {@code //foo/bar} will turn into {@code @//foo/bar}.
+   *
+   * <p>Labels that begin with a repository name will undergo {@code repositoryMapping}.
    *
    * @param absName label-like string to be parsed
-   * @param defaultToMain Treat labels in the default repository as being in the main one instead.
    * @param repositoryMapping map of repository names from the local name found in the current
    *     repository to the global name declared in the main repository
    */
-  public static Label parseAbsolute(
-      String absName, boolean defaultToMain, RepositoryMapping repositoryMapping)
+  // TODO(b/200024947): Remove this.
+  public static Label parseAbsolute(String absName, RepositoryMapping repositoryMapping)
       throws LabelSyntaxException {
     Preconditions.checkNotNull(repositoryMapping);
-    String repo = defaultToMain ? "@" : RepositoryName.DEFAULT_REPOSITORY;
-    int packageStartPos = absName.indexOf("//");
-    if (packageStartPos > 0) {
-      repo = absName.substring(0, packageStartPos);
-      absName = absName.substring(packageStartPos);
-    } else if (absName.startsWith("@")) {
-      repo = absName;
-      absName = "//:" + absName.substring(1);
-    }
-    String error = RepositoryName.validate(repo);
-    if (error != null) {
-      throw new LabelSyntaxException(
-          "invalid repository name '" + StringUtilities.sanitizeControlChars(repo) + "': " + error);
-    }
-    try {
-      LabelValidator.PackageAndTarget labelParts = LabelValidator.parseAbsoluteLabel(absName);
-      PackageIdentifier pkgId =
-          validatePackageName(
-              labelParts.getPackageName(), labelParts.getTargetName(), repo, repositoryMapping);
-      PathFragment packageFragment = pkgId.getPackageFragment();
-      if (repo.isEmpty() && ABSOLUTE_PACKAGE_NAMES.contains(packageFragment)) {
-        pkgId = PackageIdentifier.create(RepositoryName.MAIN, packageFragment);
-      }
-      return create(pkgId, labelParts.getTargetName());
-    } catch (BadLabelException e) {
-      throw new LabelSyntaxException(e.getMessage());
-    }
+    return parseWithRepoContext(absName, RepositoryName.MAIN, repositoryMapping);
   }
 
+  // TODO(b/200024947): Remove this.
   public static Label parseAbsolute(
-      String absName,
-      boolean defaultToMain,
-      ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
+      String absName, ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
       throws LabelSyntaxException {
-    return parseAbsolute(
-        absName, defaultToMain, RepositoryMapping.createAllowingFallback(repositoryMapping));
+    return parseAbsolute(absName, RepositoryMapping.createAllowingFallback(repositoryMapping));
   }
 
   /**
@@ -185,20 +172,15 @@ public static Label parseAbsolute(
    *
    * <p>Do not use this when the argument is not hard-wired.
    */
-  @Deprecated
-  // TODO(b/110698008): create parseAbsoluteUnchecked that passes repositoryMapping
-  public static Label parseAbsoluteUnchecked(String absName, boolean defaultToMain) {
+  // TODO(b/200024947): Remove this.
+  public static Label parseAbsoluteUnchecked(String absName) {
     try {
-      return parseAbsolute(absName, defaultToMain, /* repositoryMapping= */ ImmutableMap.of());
+      return parseCanonical(absName);
     } catch (LabelSyntaxException e) {
       throw new IllegalArgumentException(e);
     }
   }
 
-  public static Label parseAbsoluteUnchecked(String absName) {
-    return parseAbsoluteUnchecked(absName, true);
-  }
-
   /**
    * Factory for Labels from separate components.
    *
@@ -208,17 +190,23 @@ public static Label parseAbsoluteUnchecked(String absName) {
    *     LabelValidator#validateTargetName}.
    * @throws LabelSyntaxException if either of the arguments was invalid.
    */
+  // TODO(b/200024947): Remove this...?
   public static Label create(String packageName, String targetName) throws LabelSyntaxException {
-    return create(validatePackageName(packageName, targetName), targetName);
+    return createUnvalidated(
+        PackageIdentifier.parse(packageName),
+        validateAndProcessTargetName(packageName, targetName));
   }
 
   /**
    * Similar factory to above, but takes a package identifier to allow external repository labels to
    * be created.
    */
+  // TODO(b/200024947): Remove this...?
   public static Label create(PackageIdentifier packageId, String targetName)
       throws LabelSyntaxException {
-    return createUnvalidated(packageId, validateTargetName(packageId, targetName));
+    return createUnvalidated(
+        packageId,
+        validateAndProcessTargetName(packageId.getPackageFragment().getPathString(), targetName));
   }
 
   /**
@@ -239,14 +227,15 @@ public static Label createUnvalidated(PackageIdentifier packageIdentifier, Strin
   }
 
   /**
-   * Resolves a relative label using a workspace-relative path to the current working directory. The
-   * method handles these cases:
+   * Parses and resolves a label string relative to the given workspace-relative directory.
    *
    * <ul>
-   *   <li>The label is absolute.
-   *   <li>The label starts with a colon.
-   *   <li>The label consists of a relative path, a colon, and a local part.
-   *   <li>The label consists only of a local part.
+   *   <li>If the input is an absolute label, it is parsed as normal.
+   *   <li>If the input starts with a colon or does not contain a colon, the package path is taken
+   *       to be the working directory, and the part after the leading colon (if present) is taken
+   *       to be the target.
+   *   <li>If the input has a non-empty part before a colon, it is appended to the working directory
+   *       to form the package path, and the part after the colon is taken as the target.
    * </ul>
    *
    * <p>Note that this method does not support any of the special syntactic constructs otherwise
@@ -258,70 +247,22 @@ public static Label createUnvalidated(PackageIdentifier packageIdentifier, Strin
    *
    * @throws LabelSyntaxException if the resulting label is not valid
    */
-  public static Label parseCommandLineLabel(String label, PathFragment workspaceRelativePath)
+  public static Label parseCommandLineLabel(String raw, PathFragment workspaceRelativePath)
       throws LabelSyntaxException {
     Preconditions.checkArgument(!workspaceRelativePath.isAbsolute());
-    if (LabelValidator.isAbsolute(label)) {
-      return parseAbsolute(label, RepositoryMapping.ALWAYS_FALLBACK);
-    }
-    int index = label.indexOf(':');
-    if (index < 0) {
-      index = 0;
-      label = ":" + label;
-    }
-    PathFragment path = workspaceRelativePath.getRelative(label.substring(0, index));
-    // Use the String, String constructor, to make sure that the package name goes through the
-    // validity check.
-    return create(path.getPathString(), label.substring(index + 1));
-  }
-
-  /**
-   * Validates the given target name and returns a normalized name if it is valid. Otherwise it
-   * throws a SyntaxException.
-   */
-  private static String validateTargetName(PackageIdentifier packageIdentifier, String name)
-      throws LabelSyntaxException {
-    String error = LabelValidator.validateTargetName(name);
-    if (error != null) {
-      error = "invalid target name '" + StringUtilities.sanitizeControlChars(name) + "': " + error;
-      if (packageIdentifier.getPackageFragment().getPathString().endsWith("/" + name)) {
-        error += " (perhaps you meant \":" + name + "\"?)";
-      }
-      throw new LabelSyntaxException(error);
-    }
-
-    // TODO(bazel-team): This should be an error, but we can't make it one for legacy reasons.
-    if (name.endsWith("/.")) {
-      name = name.substring(0, name.length() - 2);
-    }
-    return name;
-  }
-
-  private static PackageIdentifier validatePackageName(String packageIdentifier, String name)
-      throws LabelSyntaxException {
-    return validatePackageName(
-        packageIdentifier, name, /* repo= */ null, /* repositoryMapping= */ null);
-  }
-
-  /**
-   * Validates the given package name and returns a canonical {@link PackageIdentifier} instance if
-   * it is valid. Otherwise it throws a SyntaxException.
-   */
-  private static PackageIdentifier validatePackageName(
-      String packageIdentifier, String name, String repo, RepositoryMapping repositoryMapping)
-      throws LabelSyntaxException {
-    try {
-      return PackageIdentifier.parse(packageIdentifier, repo, repositoryMapping);
-    } catch (LabelSyntaxException e) {
-      String error = "invalid package name '" + packageIdentifier + "': " + e.getMessage();
-      // This check is just for a more helpful error message
-      // i.e. valid target name, invalid package name, colon-free label form
-      // used => probably they meant "//foo:bar.c" not "//foo/bar.c".
-      if (packageIdentifier.endsWith("/" + name)) {
-        error += " (perhaps you meant \":" + name + "\"?)";
-      }
-      throw new LabelSyntaxException(error);
+    Parts parts = Parts.parse(raw);
+    PathFragment pathFragment;
+    if (parts.repo == null && !parts.pkgIsAbsolute) {
+      pathFragment = workspaceRelativePath.getRelative(parts.pkg);
+    } else {
+      pathFragment = PathFragment.create(parts.pkg);
     }
+    // TODO(b/200024947): This method will eventually need to take a repo mapping too.
+    RepositoryName repoName =
+        parts.repo == null
+            ? RepositoryName.MAIN
+            : RepositoryName.createFromValidStrippedName(parts.repo);
+    return create(PackageIdentifier.create(repoName, pathFragment), parts.target);
   }
 
   /** The name and repository of the package. */
@@ -565,27 +506,17 @@ public interface HasRepoMapping {
    * @param repositoryMapping the map of local repository names in external repository to global
    *     repository names in main repo; can be empty, but not null
    */
+  // TODO(b/200024947): Remove this.
   public Label getRelativeWithRemapping(String relName, RepositoryMapping repositoryMapping)
       throws LabelSyntaxException {
     Preconditions.checkNotNull(repositoryMapping);
     if (relName.isEmpty()) {
       throw new LabelSyntaxException("empty package-relative label");
     }
-
-    if (LabelValidator.isAbsolute(relName)) {
-      // If this label is in the main repository, default the new label to the main repo as well to
-      // save resolveRepositoryRelative some work.
-      return resolveRepositoryRelative(
-          parseAbsolute(relName, /*defaultToMain=*/ getRepository().isMain(), repositoryMapping));
-    } else if (relName.equals(":")) {
-      throw new LabelSyntaxException("':' is not a valid package-relative label");
-    } else if (relName.charAt(0) == ':') {
-      return getLocalTargetLabel(relName.substring(1));
-    } else {
-      return getLocalTargetLabel(relName);
-    }
+    return parseWithPackageContext(relName, packageIdentifier, repositoryMapping);
   }
 
+  // TODO(b/200024947): Remove this.
   public Label getRelativeWithRemapping(
       String relName, ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
       throws LabelSyntaxException {
@@ -593,33 +524,6 @@ public Label getRelativeWithRemapping(
         relName, RepositoryMapping.createAllowingFallback(repositoryMapping));
   }
 
-  /**
-   * Resolves the repository of a label in the context of another label.
-   *
-   * <p>This is necessary so that dependency edges in remote repositories do not need to explicitly
-   * mention their repository name. Otherwise, referring to e.g. <code>//a:b</code> in a remote
-   * repository would point back to the main repository, which is usually not what is intended.
-   *
-   * <p>The return value will not be in the default repository.
-   */
-  public Label resolveRepositoryRelative(Label relative) {
-    if (packageIdentifier.getRepository().isDefault()
-        || !relative.packageIdentifier.getRepository().isDefault()) {
-      return relative;
-    }
-
-    try {
-      return create(
-          PackageIdentifier.create(
-              packageIdentifier.getRepository(), relative.getPackageFragment()),
-          relative.name);
-    } catch (LabelSyntaxException e) {
-      // We are creating the new label from an existing one which is guaranteed to be valid, so this
-      // can't happen.
-      throw new IllegalStateException(e);
-    }
-  }
-
   @Override
   public SkyFunctionName functionName() {
     return TRANSITIVE_TRAVERSAL;
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/LabelParser.java b/src/main/java/com/google/devtools/build/lib/cmdline/LabelParser.java
new file mode 100644
index 00000000000000..00612b91c91c5c
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/LabelParser.java
@@ -0,0 +1,195 @@
+// Copyright 2021 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.cmdline;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.util.StringUtilities;
+import com.google.errorprone.annotations.FormatMethod;
+import javax.annotation.Nullable;
+
+/** Utilities to help parse labels. */
+final class LabelParser {
+  /**
+   * Package names that aren't made relative to the current repository because they mean special
+   * things to Bazel.
+   */
+  private static final ImmutableSet<String> ABSOLUTE_PACKAGE_NAMES =
+      ImmutableSet.of(
+          // Used for select's `//conditions:default` label (not a target)
+          "conditions",
+          // Used for the public and private visibility labels (not targets)
+          "visibility",
+          // There is only one //external package
+          LabelConstants.EXTERNAL_PACKAGE_NAME.getPathString());
+
+  private LabelParser() {}
+
+  /**
+   * Contains the parsed elements of a label string. The parts are validated (they don't contain
+   * invalid characters). See {@link #parse} for valid label patterns.
+   */
+  static final class Parts {
+    /**
+     * The {@code @repo} part of the string (sans the {@literal @}); can be null if it doesn't have
+     * such a part.
+     */
+    @Nullable final String repo;
+    /** Whether the package part of the string is prefixed by double-slash. */
+    final boolean pkgIsAbsolute;
+    /** The package part of the string (sans double-slash, if any). */
+    final String pkg;
+    /** The target part of the string (sans colon). */
+    final String target;
+    /** The original unparsed raw string. */
+    final String raw;
+
+    private Parts(
+        @Nullable String repo, boolean pkgIsAbsolute, String pkg, String target, String raw) {
+      this.repo = repo;
+      this.pkgIsAbsolute = pkgIsAbsolute;
+      this.pkg = pkg;
+      this.target = target;
+      this.raw = raw;
+    }
+
+    private static Parts validateAndCreate(
+        @Nullable String repo, boolean pkgIsAbsolute, String pkg, String target, String raw)
+        throws LabelSyntaxException {
+      return new Parts(
+          validateAndProcessRepoName(repo, pkg),
+          pkgIsAbsolute,
+          validateAndProcessPackageName(pkg, target),
+          validateAndProcessTargetName(pkg, target),
+          raw);
+    }
+
+    /**
+     * Parses a raw label string into parts. The logic can be summarized by the following table:
+     *
+     * {@code
+     *  raw                 | repo   | pkgIsAbsolute | pkg       | target
+     * ---------------------+--------+---------------+-----------+-----------
+     *  foo/bar             | null   | false         | ""        | "foo/bar"
+     *  //foo/bar           | null   | true          | "foo/bar" | "bar"
+     *  @repo               | "repo" | true          | ""        | "repo"
+     *  @repo//foo/bar      | "repo" | true          | "foo/bar" | "bar"
+     *  :quux               | null   | false         | ""        | "quux"
+     *  foo/bar:quux        | null   | false         | "foo/bar" | "quux"
+     *  //foo/bar:quux      | null   | true          | "foo/bar" | "quux"
+     *  @repo//foo/bar:quux | "repo" | true          | "foo/bar" | "quux"
+     * }
+     */
+    static Parts parse(String rawLabel) throws LabelSyntaxException {
+      @Nullable final String repo;
+      final int startOfPackage;
+      final int doubleSlashIndex = rawLabel.indexOf("//");
+      final boolean pkgIsAbsolute;
+      if (rawLabel.startsWith("@")) {
+        if (doubleSlashIndex < 0) {
+          // Special case: the label "@foo" is synonymous with "@foo//:foo".
+          repo = rawLabel.substring(1);
+          return validateAndCreate(
+              repo, /*pkgIsAbsolute=*/ true, /*pkg=*/ "", /*target=*/ repo, rawLabel);
+        } else {
+          repo = rawLabel.substring(1, doubleSlashIndex);
+          startOfPackage = doubleSlashIndex + 2;
+          pkgIsAbsolute = true;
+        }
+      } else {
+        // If the label begins with '//', it's an absolute label. Otherwise, treat it as relative
+        // (the command-line kind).
+        pkgIsAbsolute = doubleSlashIndex == 0;
+        startOfPackage = doubleSlashIndex == 0 ? 2 : 0;
+        repo = null;
+      }
+
+      final String pkg;
+      final String target;
+      final int colonIndex = rawLabel.indexOf(':', startOfPackage);
+      if (colonIndex >= 0) {
+        pkg = rawLabel.substring(startOfPackage, colonIndex);
+        target = rawLabel.substring(colonIndex + 1);
+      } else if (pkgIsAbsolute) {
+        // Special case: the label "[@repo]//foo/bar" is synonymous with "[@repo]//foo/bar:bar".
+        pkg = rawLabel.substring(startOfPackage);
+        // The target name is the last package segment (works even if `pkg` contains no slash)
+        target = pkg.substring(pkg.lastIndexOf('/') + 1);
+      } else {
+        // Special case: the label "foo/bar" is synonymous with ":foo/bar".
+        pkg = "";
+        target = rawLabel.substring(startOfPackage);
+      }
+      return validateAndCreate(repo, pkgIsAbsolute, pkg, target, rawLabel);
+    }
+
+    @Nullable
+    private static String validateAndProcessRepoName(@Nullable String repo, String pkg)
+        throws LabelSyntaxException {
+      if (repo == null && ABSOLUTE_PACKAGE_NAMES.contains(pkg)) {
+        // These package names when used without a "@" part are always absolutely in the main repo.
+        return "";
+      }
+      if (repo == null) {
+        return null;
+      }
+      String error = RepositoryName.validate('@' + repo);
+      if (error != null) {
+        throw syntaxErrorf("invalid repository name '@%s': %s", repo, error);
+      }
+      return repo;
+    }
+
+    private static String validateAndProcessPackageName(String pkg, String target)
+        throws LabelSyntaxException {
+      String pkgError = LabelValidator.validatePackageName(pkg);
+      if (pkgError != null) {
+        throw syntaxErrorf(
+            "invalid package name '%s': %s%s", pkg, pkgError, perhapsYouMeantMessage(pkg, target));
+      }
+      return pkg;
+    }
+
+    void checkPkgIsAbsolute() throws LabelSyntaxException {
+      if (!pkgIsAbsolute) {
+        throw syntaxErrorf("invalid label '%s': absolute label must begin with '@' or '//'", raw);
+      }
+    }
+  }
+
+  @FormatMethod
+  static LabelSyntaxException syntaxErrorf(String format, Object... args) {
+    return new LabelSyntaxException(
+        StringUtilities.sanitizeControlChars(String.format(format, args)));
+  }
+
+  private static String perhapsYouMeantMessage(String pkg, String target) {
+    return pkg.endsWith('/' + target) ? " (perhaps you meant \":" + target + "\"?)" : "";
+  }
+
+  static String validateAndProcessTargetName(String pkg, String target)
+      throws LabelSyntaxException {
+    String targetError = LabelValidator.validateTargetName(target);
+    if (targetError != null) {
+      throw syntaxErrorf(
+          "invalid target name '%s': %s%s",
+          target, targetError, perhapsYouMeantMessage(pkg, target));
+    }
+    // TODO(bazel-team): This should be an error, but we can't make it one for legacy reasons.
+    if (target.endsWith("/.")) {
+      return target.substring(0, target.length() - 2);
+    }
+    return target;
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index 3cbe4c446286ad..b2eda75ddc3491 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -24,11 +24,8 @@
 import javax.annotation.concurrent.Immutable;
 
 /**
- * Uniquely identifies a package, given a repository name and a package's path fragment.
- *
- * <p>The repository the build is happening in is the <i>default workspace</i>, and is identified by
- * the workspace name "". Other repositories can be named in the WORKSPACE file. These workspaces
- * are prefixed by {@literal @}.
+ * Uniquely identifies a package. Contains the (canonical) name of the repository this package lives
+ * in, and the package's path fragment.
  */
 @AutoCodec
 @Immutable
@@ -114,44 +111,15 @@ private PackageIdentifier(RepositoryName repository, PathFragment pkgName) {
   }
 
   public static PackageIdentifier parse(String input) throws LabelSyntaxException {
-    return parse(input, /* repo= */ null, /* repositoryMapping= */ null);
-  }
-
-  public static PackageIdentifier parse(
-      String input, String repo, RepositoryMapping repositoryMapping) throws LabelSyntaxException {
-    String packageName;
-    int packageStartPos = input.indexOf("//");
-    if (repo != null) {
-      packageName = input;
-    } else if (input.startsWith("@") && packageStartPos > 0) {
-      repo = input.substring(0, packageStartPos);
-      packageName = input.substring(packageStartPos + 2);
-    } else if (input.startsWith("@")) {
-      throw new LabelSyntaxException("starts with a '@' but does not contain '//'");
-    } else if (packageStartPos == 0) {
-      repo = RepositoryName.DEFAULT_REPOSITORY;
-      packageName = input.substring(2);
-    } else {
-      repo = RepositoryName.DEFAULT_REPOSITORY;
-      packageName = input;
-    }
-
-    String error = RepositoryName.validate(repo);
-    if (error != null) {
-      throw new LabelSyntaxException(error);
-    }
-
-    error = LabelValidator.validatePackageName(packageName);
-    if (error != null) {
-      throw new LabelSyntaxException(error);
-    }
-
-    if (repositoryMapping == null) {
-      return create(repo, PathFragment.create(packageName));
+    if (input.contains(":")) {
+      throw LabelParser.syntaxErrorf("invalid package identifier '%s': contains ':'", input);
     }
-
-    return create(
-        repositoryMapping.get(RepositoryName.create(repo)), PathFragment.create(packageName));
+    LabelParser.Parts parts = LabelParser.Parts.parse(input + ":dummy_target");
+    RepositoryName repoName =
+        parts.repo == null
+            ? RepositoryName.MAIN
+            : RepositoryName.createFromValidStrippedName(parts.repo);
+    return create(repoName, PathFragment.create(parts.pkg));
   }
 
   public RepositoryName getRepository() {
@@ -175,8 +143,9 @@ public PathFragment getSourceRoot() {
    * this is in the main repository or siblingRepositoryLayout is true. Otherwise, returns
    * external/[repository name]/[pkgName].
    */
+  // TODO(bazel-team): Rename getDerivedArtifactPath or similar.
   public PathFragment getPackagePath(boolean siblingRepositoryLayout) {
-    return repository.isDefault() || repository.isMain() || siblingRepositoryLayout
+    return repository.isMain() || siblingRepositoryLayout
         ? pkgName
         : LabelConstants.EXTERNAL_PATH_PREFIX
             .getRelative(repository.strippedName())
@@ -195,30 +164,28 @@ public PathFragment getRunfilesPath() {
     return repository.getRunfilesPath().getRelative(pkgName);
   }
 
-  public PackageIdentifier makeAbsolute() {
-    if (!repository.isDefault()) {
-      return this;
-    }
-
-    return create(RepositoryName.MAIN, pkgName);
-  }
-
-  /** Returns the package in label syntax format. */
+  /**
+   * Returns the package in label syntax format.
+   *
+   * <p>Packages in the main repo are formatted without a repo qualifier.
+   */
+  // TODO(bazel-team): Maybe rename to "getDefaultForm"?
   public String getCanonicalForm() {
     String repository = getRepository().getCanonicalForm();
     return repository + "//" + getPackageFragment();
   }
 
   /**
-   * Returns the name of this package.
+   * Returns the package path, possibly qualified with a repository name.
    *
-   * <p>There are certain places that expect the path fragment as the package name ('foo/bar') as a
-   * package identifier. This isn't specific enough for packages in other repositories, so their
-   * stringified version is '@baz//foo/bar'.
+   * <p>Packages that live in the main repo are stringified without a "@" qualifier or "//"
+   * separator (e.g. "foo/bar"). All other packages include these (e.g. "@repo//foo/bar").
    */
+  // TODO(bazel-team): The absence of "//" for the main repo seems strange. Can we eliminate
+  // that disparity?
   @Override
   public String toString() {
-    return (repository.isDefault() || repository.isMain() ? "" : repository + "//") + pkgName;
+    return (repository.isMain() ? "" : repository + "//") + pkgName;
   }
 
   @Override
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryMapping.java b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryMapping.java
index 5e2bbe5460e727..54d1dca1a92dd7 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryMapping.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryMapping.java
@@ -79,11 +79,9 @@ public RepositoryMapping withAdditionalMappings(RepositoryMapping additionalMapp
   }
 
   public RepositoryName get(RepositoryName repositoryName) {
-    // 1. Default repo ("") should always map to default repo
-    // 2. @bazel_tools is a special repo that should be visible to all repositories.
-    // 3. @local_config_platform is a special repo that should be visible to all repositories.
-    if (repositoryName.equals(RepositoryName.DEFAULT)
-        || repositoryName.equals(RepositoryName.BAZEL_TOOLS)
+    // 1. @bazel_tools is a special repo that should be visible to all repositories.
+    // 2. @local_config_platform is a special repo that should be visible to all repositories.
+    if (repositoryName.equals(RepositoryName.BAZEL_TOOLS)
         || repositoryName.equals(RepositoryName.LOCAL_CONFIG_PLATFORM)) {
       return repositoryName;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
index e2edc6b2d1e6a6..4ea21107dde2b2 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
@@ -32,11 +32,6 @@
 /** The name of an external repository. */
 public final class RepositoryName {
 
-  static final String DEFAULT_REPOSITORY = "";
-
-  @SerializationConstant
-  public static final RepositoryName DEFAULT = new RepositoryName(DEFAULT_REPOSITORY);
-
   @SerializationConstant
   public static final RepositoryName BAZEL_TOOLS = new RepositoryName("@bazel_tools");
 
@@ -71,10 +66,8 @@ public final class RepositoryName {
    * @throws LabelSyntaxException if the name is invalid
    */
   public static RepositoryName create(String name) throws LabelSyntaxException {
-    if (name.isEmpty()) {
-      return DEFAULT;
-    }
-    if (name.equals("@")) {
+    // TODO(b/200024947): Get rid of the '@'.
+    if (name.isEmpty() || name.equals("@")) {
       return MAIN;
     }
     try {
@@ -90,6 +83,12 @@ public static RepositoryName create(String name) throws LabelSyntaxException {
    * directory that has been created via getSourceRoot() or getPathUnderExecRoot().
    */
   public static RepositoryName createFromValidStrippedName(String name) {
+    if (name.isEmpty()) {
+      // NOTE(wyv): Without this `if` clause, a lot of Google-internal integration tests would start
+      //   failing. This suggests to me that something is comparing RepositoryName objects using
+      //   reference equality instead of #equals().
+      return MAIN;
+    }
     return repositoryNameCache.get("@" + name);
   }
 
@@ -231,6 +230,7 @@ public String getName() {
    * Returns the repository name, except that the main repo is conflated with the default repo
    * ({@code "@"} becomes the empty string).
    */
+  // TODO(bazel-team): Consider renaming to "getDefaultForm".
   public String getCanonicalForm() {
     return isMain() ? "" : name;
   }
@@ -243,7 +243,7 @@ public String getCanonicalForm() {
    * __main__), instead of "$execroot/external/repo".
    */
   public PathFragment getExecPath(boolean siblingRepositoryLayout) {
-    if (isDefault() || isMain()) {
+    if (isMain()) {
       return PathFragment.EMPTY_FRAGMENT;
     }
     PathFragment prefix =
@@ -258,8 +258,9 @@ public PathFragment getExecPath(boolean siblingRepositoryLayout) {
    */
   // TODO(kchodorow): remove once execroot is reorg-ed.
   public PathFragment getRunfilesPath() {
-    return isDefault() || isMain()
-        ? PathFragment.EMPTY_FRAGMENT : PathFragment.create("..").getRelative(strippedName());
+    return isMain()
+        ? PathFragment.EMPTY_FRAGMENT
+        : PathFragment.create("..").getRelative(strippedName());
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/TargetPattern.java b/src/main/java/com/google/devtools/build/lib/cmdline/TargetPattern.java
index 8f830057cf9f95..8cfdf70761dbd1 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/TargetPattern.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/TargetPattern.java
@@ -421,7 +421,6 @@ private TargetsInPackage(
         boolean rulesOnly,
         boolean checkWildcardConflict) {
       super(originalPattern);
-      Preconditions.checkArgument(!packageIdentifier.getRepository().isDefault());
       this.packageIdentifier = packageIdentifier;
       this.suffix = Preconditions.checkNotNull(suffix);
       this.wasOriginallyAbsolute = wasOriginallyAbsolute;
@@ -551,7 +550,6 @@ public static final class TargetsBelowDirectory extends TargetPattern {
     private TargetsBelowDirectory(
         String originalPattern, PackageIdentifier directory, boolean rulesOnly) {
       super(originalPattern);
-      Preconditions.checkArgument(!directory.getRepository().isDefault());
       this.directory = Preconditions.checkNotNull(directory);
       this.rulesOnly = rulesOnly;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/packages/AbstractAttributeMapper.java b/src/main/java/com/google/devtools/build/lib/packages/AbstractAttributeMapper.java
index df8c11c9248e1d..60a28ec8961fdf 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/AbstractAttributeMapper.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/AbstractAttributeMapper.java
@@ -185,8 +185,7 @@ private void visitLabels(
     Type.LabelVisitor visitor =
         (label, attribute) -> {
           if (label != null) {
-            Label absoluteLabel = ruleLabel.resolveRepositoryRelative(label);
-            consumer.accept(attribute, absoluteLabel);
+            consumer.accept(attribute, label);
           }
         };
     for (Attribute attribute : attributes) {
diff --git a/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java b/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
index 44f7a6fd4ef97e..09a84325d70093 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
@@ -222,11 +222,6 @@ public boolean requires(Aspect maybeRequiredAspect) {
     return requiredAspectClasses.contains(maybeRequiredAspect.getAspectClass());
   }
 
-  @Nullable
-  private static Label maybeGetRepositoryRelativeLabel(Rule from, @Nullable Label label) {
-    return label == null ? null : from.getLabel().resolveRepositoryRelative(label);
-  }
-
   /** Collects all attribute labels from the specified aspectDefinition. */
   public static void addAllAttributesOfAspect(
       final Rule from,
@@ -243,11 +238,10 @@ public static void forEachLabelDepFromAllAttributesOfAspect(
       BiConsumer<Attribute, Label> consumer) {
     LabelVisitor labelVisitor =
         (label, aspectAttribute) -> {
-          Label repositoryRelativeLabel = maybeGetRepositoryRelativeLabel(from, label);
-          if (repositoryRelativeLabel == null) {
+          if (label == null) {
             return;
           }
-          consumer.accept(aspectAttribute, repositoryRelativeLabel);
+          consumer.accept(aspectAttribute, label);
         };
     for (Attribute aspectAttribute : aspect.getDefinition().attributes.values()) {
       if (!dependencyFilter.test(aspect, aspectAttribute)) {
diff --git a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
index 746d6963946b0b..452f7aa5db5529 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
@@ -249,8 +249,7 @@ public Label convert(Object x, Object what, Object context) throws ConversionExc
         String str = (String) x;
         // TODO(b/110101445): check if context is ever actually null
         if (context == null) {
-          return Label.parseAbsolute(
-              str, /* defaultToMain= */ false, /* repositoryMapping= */ ImmutableMap.of());
+          return Label.parseAbsolute(str, /* repositoryMapping= */ ImmutableMap.of());
           // TODO(b/110308446): remove instances of context being a Label
         } else if (context instanceof Label) {
           return ((Label) context).getRelativeWithRemapping(str, ImmutableMap.of());
diff --git a/src/main/java/com/google/devtools/build/lib/packages/ConfiguredAttributeMapper.java b/src/main/java/com/google/devtools/build/lib/packages/ConfiguredAttributeMapper.java
index a258d93495c46c..70e72d3fd3d0a0 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/ConfiguredAttributeMapper.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/ConfiguredAttributeMapper.java
@@ -184,8 +184,7 @@ private <T> ConfigKeyAndValue<T> resolveSelector(String attributeName, Selector<
         continue;
       }
 
-      ConfigMatchingProvider curCondition =
-          configConditions.get(getLabel().resolveRepositoryRelative(selectorKey));
+      ConfigMatchingProvider curCondition = configConditions.get(selectorKey);
       if (curCondition == null) {
         // This can happen if the rule is in error
         continue;
diff --git a/src/main/java/com/google/devtools/build/lib/packages/PackageGroupsRuleVisibility.java b/src/main/java/com/google/devtools/build/lib/packages/PackageGroupsRuleVisibility.java
index dbf46cb4c62953..934ed6f103d8c4 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/PackageGroupsRuleVisibility.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/PackageGroupsRuleVisibility.java
@@ -27,18 +27,18 @@ public class PackageGroupsRuleVisibility implements RuleVisibility {
   private final PackageGroupContents directPackages;
   private final List<Label> declaredLabels;
 
-  private PackageGroupsRuleVisibility(Label ruleLabel, List<Label> labels) {
+  // TODO(b/200024947): Remove the unused argument.
+  private PackageGroupsRuleVisibility(Label unusedRuleLabel, List<Label> labels) {
     declaredLabels = ImmutableList.copyOf(labels);
     ImmutableList.Builder<PackageSpecification> directPackageBuilder = ImmutableList.builder();
     ImmutableList.Builder<Label> packageGroupBuilder = ImmutableList.builder();
 
     for (Label label : labels) {
-      Label resolved = ruleLabel.resolveRepositoryRelative(label);
-      PackageSpecification specification = PackageSpecification.fromLabel(resolved);
+      PackageSpecification specification = PackageSpecification.fromLabel(label);
       if (specification != null) {
         directPackageBuilder.add(specification);
       } else {
-        packageGroupBuilder.add(resolved);
+        packageGroupBuilder.add(label);
       }
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/packages/PackageSpecification.java b/src/main/java/com/google/devtools/build/lib/packages/PackageSpecification.java
index 318cab60cbe08d..a099ccf6e271a6 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/PackageSpecification.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/PackageSpecification.java
@@ -120,7 +120,7 @@ private static PackageSpecification fromStringPositive(RepositoryName repository
       throw new InvalidPackageSpecificationException(
           String.format("invalid package name '%s': %s", spec, e.getMessage()));
     }
-    Verify.verify(packageId.getRepository().isDefault());
+    Verify.verify(packageId.getRepository().isMain());
 
     PackageIdentifier packageIdForSpecifiedRepository =
         PackageIdentifier.create(repositoryName, packageId.getPackageFragment());
diff --git a/src/main/java/com/google/devtools/build/lib/pkgcache/PackageOptions.java b/src/main/java/com/google/devtools/build/lib/pkgcache/PackageOptions.java
index ca6f59321831a1..b130b52585a2a2 100644
--- a/src/main/java/com/google/devtools/build/lib/pkgcache/PackageOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/pkgcache/PackageOptions.java
@@ -225,13 +225,9 @@ public String getTypeDescription() {
   }
 
   public ImmutableSet<PackageIdentifier> getDeletedPackages() {
-    if (deletedPackages == null || deletedPackages.isEmpty()) {
+    if (deletedPackages == null) {
       return ImmutableSet.of();
     }
-    ImmutableSet.Builder<PackageIdentifier> newDeletedPackages = ImmutableSet.builder();
-    for (PackageIdentifier pkg : deletedPackages) {
-      newDeletedPackages.add(pkg.makeAbsolute());
-    }
-    return newDeletedPackages.build();
+    return ImmutableSet.copyOf(deletedPackages);
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java b/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
index 985bc35f10924e..c5c4be5cd050e0 100644
--- a/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
+++ b/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
@@ -14,7 +14,6 @@
 package com.google.devtools.build.lib.pkgcache;
 
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.Preconditions;
 import com.google.common.base.Verify;
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.cmdline.LabelConstants;
@@ -106,7 +105,6 @@ public Path getPackageBuildFile(PackageIdentifier packageName) throws NoSuchPack
   public Path getPackageBuildFileNullable(
       PackageIdentifier packageIdentifier,
       AtomicReference<? extends UnixGlob.FilesystemCalls> cache) {
-    Preconditions.checkArgument(!packageIdentifier.getRepository().isDefault());
     if (packageIdentifier.getRepository().isMain()) {
       for (BuildFileName buildFileName : buildFilesByPriority) {
         Path buildFilePath =
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
index 6a0b0ad71b2cce..f2005eb1df1536 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
@@ -1033,8 +1033,7 @@ private CcCompilationContext.Builder initializeCcCompilationContext(RuleContext
     ccCompilationContextBuilder.addFrameworkIncludeDirs(frameworkIncludeDirs);
 
     boolean external =
-        !repositoryName.isDefault()
-            && !repositoryName.isMain()
+        !repositoryName.isMain()
             && featureConfiguration.isEnabled(CppRuleClasses.EXTERNAL_INCLUDE_PATHS);
 
     if (external) {
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaCompileActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaCompileActionBuilder.java
index 0a8711914b990a..20a9da7968bdd5 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaCompileActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaCompileActionBuilder.java
@@ -322,7 +322,7 @@ private CustomCommandLine buildParamFileContents(ImmutableList<String> javacOpts
     }
     if (targetLabel != null) {
       result.add("--target_label");
-      if (targetLabel.getRepository().isDefault() || targetLabel.getRepository().isMain()) {
+      if (targetLabel.getRepository().isMain()) {
         result.addLabel(targetLabel);
       } else {
         // @-prefixed strings will be assumed to be filenames and expanded by
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaHeaderCompileActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaHeaderCompileActionBuilder.java
index e079e1ae087073..c322839b70f8f2 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaHeaderCompileActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaHeaderCompileActionBuilder.java
@@ -351,7 +351,7 @@ public void build(JavaToolchainProvider javaToolchain) throws InterruptedExcepti
 
     if (targetLabel != null) {
       commandLine.add("--target_label");
-      if (targetLabel.getRepository().isDefault() || targetLabel.getRepository().isMain()) {
+      if (targetLabel.getRepository().isMain()) {
         commandLine.addLabel(targetLabel);
       } else {
         // @-prefixed strings will be assumed to be params filenames and expanded,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntime.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntime.java
index 86c3228f06dc58..63b15b604aba22 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntime.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntime.java
@@ -127,7 +127,7 @@ private static boolean isJavaBinary(PathFragment path) {
   }
 
   static PathFragment defaultJavaHome(Label javabase, boolean siblingRepositoryLayout) {
-    if (javabase.getRepository().isDefault()) {
+    if (javabase.getRepository().isMain()) {
       return javabase.getPackageFragment();
     }
     return javabase.getPackageIdentifier().getExecPath(siblingRepositoryLayout);
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/OneVersionCheckActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/java/OneVersionCheckActionBuilder.java
index 2e4a887c345e90..f55b9a69fb1c64 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/OneVersionCheckActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/OneVersionCheckActionBuilder.java
@@ -129,7 +129,7 @@ static VectorArg<String> jarAndTargetVectorArg(NestedSet<Artifact> jarsToCheck)
 
   private static String getArtifactOwnerGeneralizedLabel(Artifact artifact) {
     Label label = checkNotNull(artifact.getOwnerLabel(), artifact);
-    return label.getRepository().isDefault() || label.getRepository().isMain()
+    return label.getRepository().isMain()
         ? label.toString()
         // Escape '@' prefix for .params file.
         : "@" + label;
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
index 2cd36863d86dd4..0f14bfdb907ca7 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
@@ -264,14 +264,6 @@ static boolean verifyMarkerDataForFiles(
 
   public static RootedPath getRootedPathFromLabel(Label label, Environment env)
       throws InterruptedException, EvalException {
-    // Look for package.
-    if (label.getRepository().isDefault()) {
-      try {
-        label = Label.create(label.getPackageIdentifier().makeAbsolute(), label.getName());
-      } catch (LabelSyntaxException e) {
-        throw new AssertionError(e); // Can't happen because the input label is valid
-      }
-    }
     SkyKey pkgSkyKey = PackageLookupValue.key(label.getPackageIdentifier());
     PackageLookupValue pkgLookupValue = (PackageLookupValue) env.getValue(pkgSkyKey);
     if (pkgLookupValue == null) {
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
index a2247fa0736881..3de8e895e7b4cc 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
@@ -885,8 +885,6 @@ static ImmutableList<Label> getLoadLabels(
       ImmutableList<Pair<String, Location>> loads,
       PackageIdentifier base,
       RepositoryMapping repoMapping) {
-    Preconditions.checkArgument(!base.getRepository().isDefault());
-
     // It's redundant that getRelativeWithRemapping needs a Label;
     // a PackageIdentifier should suffice. Make one here.
     Label buildLabel = getBUILDLabel(base);
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
index 599dfe96c9fd8e..72facd81c3e053 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
@@ -739,9 +739,7 @@ static ConfigConditions getConfigConditions(
 
     // Collect the labels of the configured targets we need to resolve.
     List<Label> configLabels =
-        attrs.get(RuleClass.CONFIG_SETTING_DEPS_ATTRIBUTE, BuildType.LABEL_LIST).stream()
-            .map(configLabel -> target.getLabel().resolveRepositoryRelative(configLabel))
-            .collect(Collectors.toList());
+        attrs.get(RuleClass.CONFIG_SETTING_DEPS_ATTRIBUTE, BuildType.LABEL_LIST);
     if (configLabels.isEmpty()) {
       return ConfigConditions.EMPTY;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
index 0323f6e6bb725b..39449b2e68cdd3 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
@@ -57,7 +57,6 @@ public String getReasonForNoContainingPackage() {
 
   public static Key key(PackageIdentifier id) {
     Preconditions.checkArgument(!id.getPackageFragment().isAbsolute(), id);
-    Preconditions.checkArgument(!id.getRepository().isDefault(), id);
     return Key.create(id);
   }
 
@@ -90,7 +89,7 @@ static String getErrorMessageForLabelCrossingPackageBoundary(
                   labelNameFragment.segmentCount())
               : label.toPathFragment().relativeTo(containingPkgFragment);
       message += "; perhaps you meant to put the colon here: '";
-      if (containingPkg.getRepository().isDefault() || containingPkg.getRepository().isMain()) {
+      if (containingPkg.getRepository().isMain()) {
         message += "//";
       }
       message += containingPkg + ":" + labelNameInContainingPackage + "'?";
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
index c68f03bc9fe052..74ae317dea92d6 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
@@ -13,7 +13,6 @@
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;
 
-import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 
@@ -656,8 +655,6 @@ static ImmutableMap<String, Module> loadBzlModules(
       List<BzlLoadValue.Key> keys,
       @Nullable BzlLoadFunction bzlLoadFunctionForInlining)
       throws NoSuchPackageException, InterruptedException {
-    checkArgument(!packageId.getRepository().isDefault());
-
     List<BzlLoadValue> bzlLoads;
     try {
       bzlLoads =
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupValue.java
index c5b7b577619bb6..562ce5e335b4d1 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupValue.java
@@ -126,7 +126,6 @@ public static SkyKey key(PathFragment directory) {
   }
 
   public static Key key(PackageIdentifier pkgIdentifier) {
-    Preconditions.checkArgument(!pkgIdentifier.getRepository().isDefault());
     return Key.create(pkgIdentifier);
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageValue.java
index 180772577717a5..0172abbd6ab1f7 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageValue.java
@@ -57,7 +57,6 @@ public String toString() {
   }
 
   public static Key key(PackageIdentifier pkgIdentifier) {
-    Preconditions.checkArgument(!pkgIdentifier.getRepository().isDefault());
     return Key.create(pkgIdentifier);
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java b/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
index 23712d1d6ca480..9dd2c4f240c35c 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
@@ -123,7 +123,7 @@ public ProcessPackageDirectoryResult getPackageExistenceAndSubdirDeps(
 
     PackageIdentifier packageId = PackageIdentifier.create(repositoryName, rootRelativePath);
 
-    if ((packageId.getRepository().isDefault() || packageId.getRepository().isMain())
+    if (packageId.getRepository().isMain()
         && fileValue.isSymlink()
         && fileValue
             .getUnresolvedLinkTarget()
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RecursivePkgKey.java b/src/main/java/com/google/devtools/build/lib/skyframe/RecursivePkgKey.java
index 25054f849a5b59..d1924148db4d7f 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RecursivePkgKey.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RecursivePkgKey.java
@@ -42,7 +42,6 @@ public RecursivePkgKey(
       RootedPath rootedPath,
       ImmutableSet<PathFragment> excludedPaths) {
     PathFragment.checkAllPathsAreUnder(excludedPaths, rootedPath.getRootRelativePath());
-    Preconditions.checkState(!repositoryName.isDefault());
     this.repositoryName = repositoryName;
     this.rootedPath = Preconditions.checkNotNull(rootedPath);
     this.excludedPaths = Preconditions.checkNotNull(excludedPaths);
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
index 5267d3c60fb768..88470c4121fb31 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
@@ -2662,8 +2662,6 @@ Package getPackage(ExtendedEventHandler eventHandler, PackageIdentifier pkgName)
 
     /** Returns whether the given package should be consider deleted and thus should be ignored. */
     public boolean isPackageDeleted(PackageIdentifier packageName) {
-      Preconditions.checkState(
-          !packageName.getRepository().isDefault(), "package must be absolute: %s", packageName);
       return deletedPackages.get().contains(packageName);
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTargetKey.java b/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTargetKey.java
index 7fad37ebac00c4..04a942a45e5325 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTargetKey.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTargetKey.java
@@ -31,7 +31,6 @@ public final class TransitiveTargetKey implements SkyKey {
   public static final SkyFunctionName NAME = SkyFunctionName.createHermetic("TRANSITIVE_TARGET");
 
   public static TransitiveTargetKey of(Label label) {
-    Preconditions.checkArgument(!label.getRepository().isDefault());
     return new TransitiveTargetKey(label);
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTraversalValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTraversalValue.java
index 77ffabdfeeb94f..def4ca5b779c9e 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTraversalValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/TransitiveTraversalValue.java
@@ -150,7 +150,6 @@ public int hashCode() {
 
   @ThreadSafe
   public static SkyKey key(Label label) {
-    Preconditions.checkArgument(!label.getRepository().isDefault());
     return label;
   }
 
diff --git a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeStarlarkRuleFunctionsApi.java b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeStarlarkRuleFunctionsApi.java
index ac4413a667f9eb..4a95d2dea09d21 100644
--- a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeStarlarkRuleFunctionsApi.java
+++ b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeStarlarkRuleFunctionsApi.java
@@ -171,7 +171,6 @@ public Label label(String labelString, StarlarkThread thread) throws EvalExcepti
     try {
       return Label.parseAbsolute(
           labelString,
-          /* defaultToMain= */ false,
           /* repositoryMapping= */ ImmutableMap.of());
     } catch (LabelSyntaxException e) {
       throw Starlark.errorf("Illegal absolute label syntax: %s", labelString);
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/test/TestActionBuilderTest.java b/src/test/java/com/google/devtools/build/lib/analysis/test/TestActionBuilderTest.java
index 9df31fdabead55..731b1fe92a14e3 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/test/TestActionBuilderTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/test/TestActionBuilderTest.java
@@ -16,7 +16,6 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.common.eventbus.EventBus;
 import com.google.devtools.build.lib.actions.Artifact;
@@ -216,12 +215,7 @@ public void testAspectOverNonExpandingTestSuitesVisitsImplicitTests() throws Exc
     ConfiguredAspect aspectValue =
         Iterables.getOnlyElement(analysisResult.getAspectsMap().values());
     StarlarkProvider.Key key =
-        new StarlarkProvider.Key(
-            Label.parseAbsolute(
-                "//:aspect.bzl",
-                /* defaultToMain= */ true,
-                /* repositoryMapping= */ ImmutableMap.of()),
-            "StructImpl");
+        new StarlarkProvider.Key(Label.parseAbsoluteUnchecked("//:aspect.bzl"), "StructImpl");
     StructImpl info = (StructImpl) aspectValue.get(key);
     assertThat(((Depset) info.getValue("labels")).getSet(String.class).toList())
         .containsExactly("//:suite", "//:test_a", "//:test_b");
@@ -254,12 +248,7 @@ public void testAspectOverNonExpandingTestSuitesVisitsExplicitTests() throws Exc
     ConfiguredAspect aspectValue =
         Iterables.getOnlyElement(analysisResult.getAspectsMap().values());
     StarlarkProvider.Key key =
-        new StarlarkProvider.Key(
-            Label.parseAbsolute(
-                "//:aspect.bzl",
-                /* defaultToMain= */ true,
-                /* repositoryMapping= */ ImmutableMap.of()),
-            "StructImpl");
+        new StarlarkProvider.Key(Label.parseAbsoluteUnchecked("//:aspect.bzl"), "StructImpl");
     StructImpl info = (StructImpl) aspectValue.get(key);
     assertThat(((Depset) info.getValue("labels")).getSet(String.class).toList())
         .containsExactly("//:suite", "//:test_b");
@@ -288,12 +277,7 @@ public void testAspectOverExpandingTestSuitesDoesNotVisitSuite() throws Exceptio
             /* doAnalysis= */ true,
             new EventBus());
     final StarlarkProvider.Key key =
-        new StarlarkProvider.Key(
-            Label.parseAbsolute(
-                "//:aspect.bzl",
-                /* defaultToMain= */ true,
-                /* repositoryMapping= */ ImmutableMap.of()),
-            "StructImpl");
+        new StarlarkProvider.Key(Label.parseAbsoluteUnchecked("//:aspect.bzl"), "StructImpl");
 
     List<String> labels = new ArrayList<>();
     for (ConfiguredAspect a : analysisResult.getAspectsMap().values()) {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java b/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
index c8d224d772d1ee..0e6348a058a3e9 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
@@ -163,7 +163,6 @@
 import com.google.devtools.build.lib.skyframe.SkyframeExecutor;
 import com.google.devtools.build.lib.skyframe.StarlarkBuiltinsValue;
 import com.google.devtools.build.lib.skyframe.TargetPatternPhaseValue;
-import com.google.devtools.build.lib.testutil.BlazeTestUtils;
 import com.google.devtools.build.lib.testutil.FoundationTestCase;
 import com.google.devtools.build.lib.testutil.SkyframeExecutorTestHelper;
 import com.google.devtools.build.lib.testutil.TestConstants;
@@ -1020,8 +1019,7 @@ protected ConfiguredTarget getConfiguredTarget(String label, BuildConfigurationV
   @Nullable
   protected ConfiguredTarget getConfiguredTarget(Label label, BuildConfigurationValue config) {
     try {
-      return view.getConfiguredTargetForTesting(
-          reporter, BlazeTestUtils.convertLabel(label), config);
+      return view.getConfiguredTargetForTesting(reporter, label, config);
     } catch (InvalidConfigurationException
         | StarlarkTransition.TransitionException
         | InterruptedException e) {
diff --git a/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java b/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
index 30b830e2cb1c7e..1fe0dc07f9ff51 100644
--- a/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
+++ b/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
@@ -218,20 +218,6 @@ public void testGetRelativeWithRemoteRepoToDefaultRepo() throws Exception {
     assertThat(relative.getName()).isEqualTo("y");
   }
 
-  @Test
-  public void testGetRepositoryRelative() throws Exception {
-    Label defaultBase = Label.parseAbsolute("//foo/bar:baz", ImmutableMap.of());
-    Label repoBase = Label.parseAbsolute("@repo//foo/bar:baz", ImmutableMap.of());
-    Label mainBase = Label.parseAbsolute("@//foo/bar:baz", ImmutableMap.of());
-    Label externalTarget = Label.parseAbsolute("//external:target", ImmutableMap.of());
-    Label l = defaultBase.resolveRepositoryRelative(externalTarget);
-    assertThat(l.getRepository().isMain()).isTrue();
-    assertThat(l.getPackageName()).isEqualTo("external");
-    assertThat(l.getName()).isEqualTo("target");
-    assertThat(repoBase.resolveRepositoryRelative(externalTarget)).isEqualTo(l);
-    assertThat(mainBase.resolveRepositoryRelative(externalTarget)).isEqualTo(l);
-  }
-
   @Test
   public void testFactory() throws Exception {
     Label l = Label.create("foo/bar", "quux");
@@ -422,7 +408,9 @@ public void testInvalidRepo() throws Exception {
             () -> Label.parseAbsolute("foo//bar/baz:bat/boo", ImmutableMap.of()));
     assertThat(e)
         .hasMessageThat()
-        .isEqualTo("invalid repository name 'foo': workspace names must start with '@'");
+        .isEqualTo(
+            "invalid package name 'foo//bar/baz': package names may not contain '//' path"
+                + " separators");
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java b/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
index 6ab1ee8b477f23..fc3141a6dfba3f 100644
--- a/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
+++ b/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
@@ -37,7 +37,8 @@ public void assertNotValid(String name, String expectedMessage) {
   @Test
   public void testValidateRepositoryName() throws Exception {
     assertThat(RepositoryName.create("@foo").toString()).isEqualTo("@foo");
-    assertThat(RepositoryName.create("").toString()).isEmpty();
+    assertThat(RepositoryName.create("").toString()).isEqualTo("@");
+    assertThat(RepositoryName.create("")).isSameInstanceAs(RepositoryName.MAIN);
     assertThat(RepositoryName.create("@foo_bar").toString()).isEqualTo("@foo_bar");
     assertThat(RepositoryName.create("@foo-bar").toString()).isEqualTo("@foo-bar");
     assertThat(RepositoryName.create("@foo.bar").toString()).isEqualTo("@foo.bar");
diff --git a/src/test/java/com/google/devtools/build/lib/pkgcache/LoadingPhaseRunnerTest.java b/src/test/java/com/google/devtools/build/lib/pkgcache/LoadingPhaseRunnerTest.java
index 64f8f0311309a3..eaac956da2ec72 100644
--- a/src/test/java/com/google/devtools/build/lib/pkgcache/LoadingPhaseRunnerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/pkgcache/LoadingPhaseRunnerTest.java
@@ -1171,7 +1171,8 @@ public void testPatternEndingWithSingleSlashIsError() {
   public void testPatternStartingWithDotDotSlash() {
     expectError(
         "../foo",
-        "Bad target pattern '../foo': package name component contains only '.' characters");
+        "Bad target pattern '../foo': invalid package name '..': package name component contains"
+            + " only '.' characters");
   }
 
   private void runTestPackageLoadingError(boolean keepGoing, String... patterns) throws Exception {
diff --git a/src/test/java/com/google/devtools/build/lib/query2/testutil/AbstractQueryTest.java b/src/test/java/com/google/devtools/build/lib/query2/testutil/AbstractQueryTest.java
index 0dd74745994aef..9d0f1cba9ba57e 100644
--- a/src/test/java/com/google/devtools/build/lib/query2/testutil/AbstractQueryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/query2/testutil/AbstractQueryTest.java
@@ -76,11 +76,6 @@ public abstract class AbstractQueryTest<T> {
 
   private static final String DEFAULT_UNIVERSE = "//...:*";
 
-  protected static final String BAD_PACKAGE_NAME =
-      "package names may contain "
-          + "A-Z, a-z, 0-9, or any of ' !\"#$%&'()*+,-./;<=>?[]^_`{|}~' "
-          + "(most 7-bit ascii characters except 0-31, 127, ':', or '\\')";
-
   protected MockToolsConfig mockToolsConfig;
   protected QueryHelper<T> helper;
   protected AnalysisMock analysisMock;
@@ -317,7 +312,11 @@ public void testBadTargetLiterals() throws Exception {
   protected final void checkResultofBadTargetLiterals(String message, FailureDetail failureDetail) {
     assertThat(failureDetail.getTargetPatterns().getCode())
         .isEqualTo(TargetPatterns.Code.LABEL_SYNTAX_ERROR);
-    assertThat(message).isEqualTo("Invalid package name 'bad:*': " + BAD_PACKAGE_NAME);
+    // TODO(bazel-team): This error message could use some improvement. It's verbose (duplicate
+    //   message) and shows an extra "@" that wasn't in the input.
+    assertThat(message)
+        .isEqualTo(
+            "Invalid package name 'bad:*': invalid package identifier '@//bad:*': contains ':'");
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/rules/LabelBuildSettingTest.java b/src/test/java/com/google/devtools/build/lib/rules/LabelBuildSettingTest.java
index 52386c89807b48..0e1afdae573c80 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/LabelBuildSettingTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/LabelBuildSettingTest.java
@@ -281,6 +281,6 @@ public void transitionsDontAllowRelativeLabels() throws Exception {
         "rule_with_transition(name = 'buildme')");
     reporter.removeHandler(failFastHandler);
     assertThat(getConfiguredTarget("//test:buildme")).isNull();
-    assertContainsEvent("invalid label: :other_rule");
+    assertContainsEvent("invalid label ':other_rule': absolute label must begin with '@' or '//'");
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/serialization/RepositoryNameCodecTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/serialization/RepositoryNameCodecTest.java
index f9bfe33929f1c6..aeaeedac23b6d8 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/serialization/RepositoryNameCodecTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/serialization/RepositoryNameCodecTest.java
@@ -26,7 +26,6 @@ public class RepositoryNameCodecTest {
   @Test
   public void testCodec() throws Exception {
     new SerializationTester(
-            RepositoryName.create(RepositoryName.DEFAULT.getName()),
             RepositoryName.create(RepositoryName.MAIN.getName()),
             RepositoryName.create("@externalandshouldntexistinthisworkspace"))
         .runTests();
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
index fbecb9450ce8ea..b2f580fb7c068b 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
@@ -687,16 +687,17 @@ public void testLabelAttrDefaultValueAsString() throws Exception {
   public void testLabelAttrDefaultValueAsStringBadValue() throws Exception {
     ev.checkEvalErrorContains(
         "invalid label '/foo:bar' in parameter 'default' of attribute 'label': "
-            + "invalid target name '/foo:bar'",
+            + "invalid package name '/foo': package names may not start with '/'",
         "attr.label(default = '/foo:bar')");
 
     ev.checkEvalErrorContains(
         "invalid label '/bar:foo' in element 1 of parameter 'default' of attribute "
-            + "'label_list': invalid target name '/bar:foo'",
+            + "'label_list': invalid package name '/bar': package names may not start with '/'",
         "attr.label_list(default = ['//foo:bar', '/bar:foo'])");
 
     ev.checkEvalErrorContains(
-        "invalid label '/bar:foo' in dict key element: invalid target name '/bar:foo'",
+        "invalid label '/bar:foo' in dict key element: invalid package name '/bar': "
+            + "package names may not start with '/'",
         "attr.label_keyed_string_dict(default = {'//foo:bar': 'a', '/bar:foo': 'b'})");
   }
 
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/BlazeTestUtils.java b/src/test/java/com/google/devtools/build/lib/testutil/BlazeTestUtils.java
index b6b83fac334a96..452d185c3f4b5e 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/BlazeTestUtils.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/BlazeTestUtils.java
@@ -16,8 +16,6 @@
 
 import com.google.common.base.Joiner;
 import com.google.common.base.Preconditions;
-import com.google.devtools.build.lib.cmdline.Label;
-import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import java.io.File;
@@ -85,16 +83,6 @@ public static void changeModtime(Path path)
     } while (path.getLastModifiedTime() == prevMtime);
   }
 
-  public static Label convertLabel(Label label) {
-    try {
-      return label.getRepository().isDefault()
-          ? Label.create(label.getPackageIdentifier().makeAbsolute(), label.getName())
-          : label;
-    } catch (LabelSyntaxException e) {
-      throw new IllegalStateException(e);
-    }
-  }
-
   /**
    * Creates a list of arguments to pass to Bazel, with flags necessary for Bazel to work properly
    * appended to the original {@code args} array.