Verify bootclasspath version is at most compilation runtime version

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

@@ -41,6 +41,7 @@ java_library(
         "//src/main/java/com/google/devtools/build/lib/analysis:analysis_cluster",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/build_configuration",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/compilation_mode",
+        "//src/main/java/com/google/devtools/build/lib/analysis:config/core_options",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/execution_transition_factory",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/transitions/no_transition",
         "//src/main/java/com/google/devtools/build/lib/analysis:configured_target",

src/main/java/com/google/devtools/build/lib/rules/java/BootClassPathInfo.java

@@ -35,6 +35,7 @@
 import net.starlark.java.eval.NoneType;
 import net.starlark.java.eval.Sequence;
 import net.starlark.java.eval.Starlark;
+import net.starlark.java.eval.StarlarkInt;
 import net.starlark.java.eval.StarlarkThread;
 import net.starlark.java.eval.StarlarkValue;
 import net.starlark.java.syntax.Location;
@@ -74,22 +75,35 @@ private Provider() {
                   "The inputs to javac's --system flag, either a directory or a listing of files,"
                       + " which must contain at least 'release', 'lib/modules', and"
                       + " 'lib/jrt-fs.jar'"),
+          @Param(
+              name = "version",
+              positional = false,
+              named = true,
+              defaultValue = "0",
+              doc = "The major version of the runtime providing this bootclasspath."
+          ),
         },
         selfCall = true,
         useStarlarkThread = true)
     public BootClassPathInfo bootClassPathInfo(
         Sequence<?> bootClassPathList,
         Sequence<?> auxiliaryList,
         Object systemOrNone,
+        StarlarkInt version,
         StarlarkThread thread)
         throws EvalException {
       NestedSet<Artifact> systemInputs = getSystemInputs(systemOrNone);
       Optional<PathFragment> systemPath = getSystemPath(systemInputs);
+      int versionChecked = version.toInt("version");
+      if (versionChecked < 0) {
+        throw Starlark.errorf("version must be non-negative, got %d", versionChecked);
+      }
       return new BootClassPathInfo(
           getBootClassPath(bootClassPathList),
           getAuxiliary(auxiliaryList),
           systemInputs,
           systemPath,
+          versionChecked,
           thread.getCallerLocation());
     }
 
@@ -150,18 +164,21 @@ private static Optional<PathFragment> getSystemPath(NestedSet<Artifact> systemIn
   private final NestedSet<Artifact> auxiliary;
   private final NestedSet<Artifact> systemInputs;
   private final Optional<PathFragment> systemPath;
+  private final int version;
 
   private BootClassPathInfo(
       NestedSet<Artifact> bootclasspath,
       NestedSet<Artifact> auxiliary,
       NestedSet<Artifact> systemInputs,
       Optional<PathFragment> systemPath,
+      int version,
       Location creationLocation) {
     super(creationLocation);
     this.bootclasspath = bootclasspath;
     this.auxiliary = auxiliary;
     this.systemInputs = systemInputs;
     this.systemPath = systemPath;
+    this.version = version;
   }
 
   @Override
@@ -175,6 +192,7 @@ public static BootClassPathInfo create(NestedSet<Artifact> bootclasspath) {
         NestedSetBuilder.emptySet(Order.NAIVE_LINK_ORDER),
         NestedSetBuilder.emptySet(Order.NAIVE_LINK_ORDER),
         Optional.empty(),
+        0,
         null);
   }
 
@@ -184,6 +202,7 @@ public static BootClassPathInfo empty() {
         NestedSetBuilder.emptySet(Order.NAIVE_LINK_ORDER),
         NestedSetBuilder.emptySet(Order.NAIVE_LINK_ORDER),
         Optional.empty(),
+        0,
         null);
   }
 
@@ -210,6 +229,11 @@ public NestedSet<Artifact> systemInputs() {
     return systemInputs;
   }
 
+  /** The major version of the runtime providing this bootclasspath. */
+  public int version() {
+    return version;
+  }
+
   public boolean isEmpty() {
     return bootclasspath.isEmpty();
   }

src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchain.java

@@ -35,6 +35,7 @@
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.analysis.Runfiles;
 import com.google.devtools.build.lib.analysis.RunfilesProvider;
+import com.google.devtools.build.lib.analysis.config.CoreOptions;
 import com.google.devtools.build.lib.analysis.configuredtargets.PackageGroupConfiguredTarget;
 import com.google.devtools.build.lib.analysis.platform.ToolchainInfo;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
@@ -160,6 +161,17 @@ public ConfiguredTarget create(RuleContext ruleContext)
 
     JavaRuntimeInfo javaRuntime = JavaRuntimeInfo.from(ruleContext, "java_runtime");
 
+    if (javaRuntime.version() != 0 && javaRuntime.version() < bootclasspath.version()) {
+      ruleContext.attributeError("java_runtime", String.format(
+          "The version of the Java compilation toolchain's java_runtime (%d) must be at least as"
+              + " high as the version of the Java runtime that provides the bootclasspath (%d)."
+              + " Either switch to a Java toolchain with a higher version of the Java runtime or"
+              + " lower the version of --%sjava_runtime_version",
+          javaRuntime.version(), bootclasspath.version(),
+          ruleContext.getConfiguration().getOptions().get(CoreOptions.class).isExec
+              ? "tool_" : ""));
+    }
+
     JavaToolchainProvider provider =
         JavaToolchainProvider.create(
             ruleContext.getLabel(),

src/test/shell/bazel/bazel_with_jdk_test.sh

@@ -289,4 +289,65 @@ function test_bazel_compiles_with_localjdk() {
   expect_not_log "exec external/remotejdk11_linux/bin/java"
 }
 
+function test_java_runtime_greater_than_java_toolchain_runtime_version() {
+  mkdir -p pkg
+  cat >pkg/BUILD <<'EOF'
+java_binary(
+    name = "Main",
+    srcs = ["Main.java"],
+    main_class = "com.example.Main",
+)
+EOF
+
+  cat >pkg/Main.java <<'EOF'
+package com.example;
+public class Main {
+  public static void main(String[] args) {
+    System.out.println("Hello World!");
+  }
+}
+EOF
+
+  bazel build //pkg:Main \
+    --java_language_version=8 \
+    --java_runtime_version=remotejdk_20 \
+    &>"${TEST_log}" && fail "Expected build to fail"
+
+  expect_log "The version of the Java compilation toolchain's java_runtime (17) must be at least as high as the version of the Java runtime that provides the bootclasspath (20). Either switch to a Java toolchain with a higher version of the Java runtime or lower the version of --java_runtime_version"
+}
+
+function test_tool_java_runtime_greater_than_java_toolchain_runtime_version() {
+  mkdir -p pkg
+  cat >pkg/BUILD <<'EOF'
+java_binary(
+    name = "Main",
+    srcs = ["Main.java"],
+    main_class = "com.example.Main",
+)
+
+genrule(
+    name = "gen",
+    outs = ["gen.txt"],
+    tools = [":Main"],
+    cmd = "$(location :Main) > $@",
+)
+EOF
+
+  cat >pkg/Main.java <<'EOF'
+package com.example;
+public class Main {
+  public static void main(String[] args) {
+    System.out.println("Hello World!");
+  }
+}
+EOF
+
+  bazel build //pkg:gen \
+    --tool_java_language_version=8 \
+    --tool_java_runtime_version=remotejdk_20 \
+    &>"${TEST_log}" && fail "Expected build to fail"
+
+  expect_log "The version of the Java compilation toolchain's java_runtime (17) must be at least as high as the version of the Java runtime that provides the bootclasspath (20). Either switch to a Java toolchain with a higher version of the Java runtime or lower the version of --tool_java_runtime_version"
+}
+
 run_suite "Tests detection of local JDK and that Bazel executes with a bundled JDK."

tools/jdk/default_java_toolchain.bzl

@@ -241,9 +241,12 @@ def _bootclasspath_impl(ctx):
     system = [f for f in ctx.files.target_javabase if f.basename in system_files]
     if len(system) != len(system_files):
         system = None
+    version = 0
     if ctx.attr.target_javabase:
+        runtime_info = ctx.attr.target_javabase[java_common.JavaRuntimeInfo]
         inputs.extend(ctx.files.target_javabase)
-        args.add(ctx.attr.target_javabase[java_common.JavaRuntimeInfo].java_home)
+        args.add(runtime_info.java_home)
+        version = runtime_info.version
 
     ctx.actions.run(
         executable = str(host_javabase.java_executable_exec_path),
@@ -257,6 +260,7 @@ def _bootclasspath_impl(ctx):
         java_common.BootClassPathInfo(
             bootclasspath = [bootclasspath],
             system = system,
+            version = version,
         ),
         OutputGroupInfo(jar = [bootclasspath]),
     ]