Add RunfilesLibraryInfo

The new provider marks runfiles libraries as such and will be used by
both Bazel itself and language rules to emit additional information
required for executable targets to find their runfiles in the presence
of repository mappings.

Work towards bazelbuild#16124

src/main/java/com/google/devtools/build/lib/analysis/BUILD

@@ -340,6 +340,7 @@ java_library(
         ":rule_configured_object_value",
         ":rule_definition_environment",
         ":run_environment_info",
+        "runfiles_library_info",
         ":starlark/args",
         ":starlark/bazel_build_api_globals",
         ":starlark/function_transition_util",
@@ -1029,6 +1030,18 @@ java_library(
     ],
 )
 
+java_library(
+    name = "runfiles_library_info",
+    srcs = ["RunfilesLibraryInfo.java"],
+    deps = [
+        "//src/main/java/com/google/devtools/build/lib/concurrent",
+        "//src/main/java/com/google/devtools/build/lib/packages",
+        "//src/main/java/com/google/devtools/build/lib/starlarkbuildapi",
+        "//src/main/java/net/starlark/java/eval",
+        "//third_party:guava",
+    ],
+)
+
 java_library(
     name = "rule_definition_environment",
     srcs = ["RuleDefinitionEnvironment.java"],

src/main/java/com/google/devtools/build/lib/analysis/RunfilesLibraryInfo.java

@@ -0,0 +1,55 @@
+// Copyright 2022 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.analysis;
+
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.packages.BuiltinProvider;
+import com.google.devtools.build.lib.packages.NativeInfo;
+import com.google.devtools.build.lib.starlarkbuildapi.RunfilesLibraryInfoApi;
+
+/**
+ * Data-less provider that signals to direct dependents that this target is a runfiles library.
+ *
+ * <p>Rules that find this provider advertised by a dependency may use this as a signal to generate
+ * code that helps with runfiles discovery, e.g., by providing a constant containing the name of the
+ * repository that defines the rule.
+ *
+ * <p>Bazel itself uses the presence of this provider on a rule as a sign that it should include the
+ * repository mapping of the repository containing the rule in the repository mapping manifest of
+ * executable transitive dependents.
+ */
+@Immutable
+public final class RunfilesLibraryInfo extends NativeInfo implements RunfilesLibraryInfoApi {
+
+  public static final RunfilesLibraryInfoProvider PROVIDER = new RunfilesLibraryInfoProvider();
+
+  @Override
+  public RunfilesLibraryInfoProvider getProvider() {
+    return PROVIDER;
+  }
+
+  public static class RunfilesLibraryInfoProvider extends BuiltinProvider<RunfilesLibraryInfo>
+      implements RunfilesLibraryInfoApi.RunfilesLibraryInfoApiProvider {
+
+    private RunfilesLibraryInfoProvider() {
+      super("RunfilesLibraryInfo", RunfilesLibraryInfo.class);
+    }
+
+    @Override
+    public RunfilesLibraryInfoApi constructor() {
+      return new RunfilesLibraryInfo();
+    }
+  }
+}

src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkModules.java

@@ -17,6 +17,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.analysis.ActionsProvider;
 import com.google.devtools.build.lib.analysis.DefaultInfo;
+import com.google.devtools.build.lib.analysis.RunfilesLibraryInfo;
 import com.google.devtools.build.lib.analysis.OutputGroupInfo;
 import com.google.devtools.build.lib.analysis.RunEnvironmentInfo;
 import com.google.devtools.build.lib.packages.StarlarkLibrary;
@@ -46,5 +47,6 @@ public static void addPredeclared(ImmutableMap.Builder<String, Object> predeclar
     predeclared.put("Actions", ActionsProvider.INSTANCE);
     predeclared.put("DefaultInfo", DefaultInfo.PROVIDER);
     predeclared.put("RunEnvironmentInfo", RunEnvironmentInfo.PROVIDER);
+    predeclared.put("RunfilesLibraryInfo", RunfilesLibraryInfo.PROVIDER);
   }
 }

src/main/java/com/google/devtools/build/lib/starlarkbuildapi/RunfilesLibraryInfoApi.java

@@ -0,0 +1,44 @@
+// Copyright 2022 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.starlarkbuildapi;
+
+import com.google.devtools.build.docgen.annot.DocCategory;
+import com.google.devtools.build.docgen.annot.StarlarkConstructor;
+import com.google.devtools.build.lib.starlarkbuildapi.core.ProviderApi;
+import com.google.devtools.build.lib.starlarkbuildapi.core.StructApi;
+import net.starlark.java.annot.StarlarkBuiltin;
+import net.starlark.java.annot.StarlarkMethod;
+
+@StarlarkBuiltin(
+    name = "RunfilesLibraryInfo",
+    category = DocCategory.PROVIDER,
+    doc = "Signals to direct dependents as well as Bazel itself that this target is a runfiles "
+        + "library. For example, rules for compiled languages may choose to generate and compile "
+        + "additional code that gives access to the name of the repository defining the current "
+        + "target if they find this provider advertised by a direct dependency.<p>This provider "
+        + "carries no data.")
+public interface RunfilesLibraryInfoApi extends StructApi {
+
+  @StarlarkBuiltin(name = "Provider", category = DocCategory.PROVIDER, documented = false)
+  interface RunfilesLibraryInfoApiProvider extends ProviderApi {
+
+    @StarlarkMethod(
+        name = "RunfilesLibraryInfo",
+        doc = "The <code>RunfilesLibraryInfo</code> constructor.",
+        selfCall = true)
+    @StarlarkConstructor
+    RunfilesLibraryInfoApi constructor();
+  }
+}

src/test/java/com/google/devtools/build/lib/starlark/BUILD

@@ -46,6 +46,7 @@ java_test(
         "//src/main/java/com/google/devtools/build/lib/analysis:file_provider",
         "//src/main/java/com/google/devtools/build/lib/analysis:resolved_toolchain_context",
         "//src/main/java/com/google/devtools/build/lib/analysis:run_environment_info",
+        "//src/main/java/com/google/devtools/build/lib/analysis:runfiles_library_info",
         "//src/main/java/com/google/devtools/build/lib/analysis:starlark/args",
         "//src/main/java/com/google/devtools/build/lib/analysis:starlark/starlark_exec_group_collection",
         "//src/main/java/com/google/devtools/build/lib/analysis:test/analysis_test_result_info",

src/test/java/com/google/devtools/build/lib/starlark/StarlarkIntegrationTest.java

@@ -30,6 +30,7 @@
 import com.google.devtools.build.lib.analysis.FilesToRunProvider;
 import com.google.devtools.build.lib.analysis.OutputGroupInfo;
 import com.google.devtools.build.lib.analysis.RunEnvironmentInfo;
+import com.google.devtools.build.lib.analysis.RunfilesLibraryInfo;
 import com.google.devtools.build.lib.analysis.RunfilesProvider;
 import com.google.devtools.build.lib.analysis.config.StarlarkDefinedConfigTransition;
 import com.google.devtools.build.lib.analysis.configuredtargets.FileConfiguredTarget;
@@ -3652,4 +3653,36 @@ public void nonExecutableStarlarkRuleReturningTestEnvironmentProducesAWarning()
             + " non-test target has no effect",
         ImmutableSet.of(EventKind.WARNING));
   }
+
+  @Test
+  public void runfilesLibraryInfoCanBeReturnedAndQueried() throws Exception {
+    scratch.file(
+        "examples/rules.bzl",
+        "def my_runfiles_library_impl(ctx):",
+        "  return [RunfilesLibraryInfo()]",
+        "my_runfiles_library = rule(implementation = my_runfiles_library_impl)",
+        "def language_rule_impl(ctx):",
+        "  if RunfilesLibraryInfo not in ctx.attr.dep:",
+        "    fail('dep does not advertise RunfilesLibraryInfo')",
+        "language_rule = rule(",
+        "  implementation = language_rule_impl,",
+        "  attrs = {'dep': attr.label()},",
+        ")"
+    );
+    scratch.file(
+        "examples/BUILD",
+        "load(':rules.bzl', 'language_rule', 'my_runfiles_library')",
+        "my_runfiles_library(name = 'runfiles_library')",
+        "language_rule(",
+        "  name = 'target',",
+        "  dep = ':runfiles_library',",
+        ")"
+    );
+
+    ConfiguredTarget runfilesLibrary = getConfiguredTarget("//examples:runfiles_library");
+    assertThat(runfilesLibrary.get(RunfilesLibraryInfo.PROVIDER)).isNotNull();
+
+    // Succeeds only if targets can be queried for the presence of RunfilesLibraryInfo in Starlark.
+    getConfiguredTarget("//examples:target");
+  }
 }