Verify that Java language level isn't higher than runtime version

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

@@ -18,11 +18,13 @@
 import com.google.auto.value.AutoValue;
 import com.google.common.base.Ascii;
 import com.google.common.base.Optional;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.analysis.PlatformOptions;
 import com.google.devtools.build.lib.analysis.config.BuildOptions;
 import com.google.devtools.build.lib.analysis.config.CoreOptionConverters.StrictDepsMode;
+import com.google.devtools.build.lib.analysis.config.CoreOptions;
 import com.google.devtools.build.lib.analysis.config.Fragment;
 import com.google.devtools.build.lib.analysis.config.InvalidConfigurationException;
 import com.google.devtools.build.lib.analysis.config.RequiresOptions;
@@ -207,6 +209,9 @@ public JavaConfiguration(BuildOptions buildOptions) throws InvalidConfigurationE
               + " --tool_java_runtime_version). This may result in incorrect toolchain selection "
               + "(see https://github.com/bazelbuild/bazel/issues/7849).");
     }
+
+    checkLanguageAndRuntimeVersion(javaOptions.javaLanguageVersion, javaOptions.javaRuntimeVersion,
+        buildOptions.get(CoreOptions.class).isExec);
   }
 
   private static void checkLegacyToolchainFlagIsUnset(String flag, Label label)
@@ -218,6 +223,58 @@ private static void checkLegacyToolchainFlagIsUnset(String flag, Label label)
     }
   }
 
+  private static void checkLanguageAndRuntimeVersion(@Nullable String rawLanguageVersion,
+      @Nullable String rawRuntimeVersion, boolean isExec) throws InvalidConfigurationException {
+    int languageVersion;
+    if (Strings.isNullOrEmpty(rawLanguageVersion)) {
+      return;
+    }
+    try {
+      languageVersion = Integer.parseUnsignedInt(rawLanguageVersion);
+    } catch (NumberFormatException e) {
+      // This is unexpected, but for the sake of compatibility with unusual toolchains, we should
+      // not fail the build.
+      return;
+    }
+
+    int runtimeVersion;
+    if (Strings.isNullOrEmpty(rawRuntimeVersion)) {
+      return;
+    }
+    int lastUnderscore = rawRuntimeVersion.lastIndexOf('_');
+    String rawRuntimeVersionLastPart;
+    if (lastUnderscore == -1) {
+      rawRuntimeVersionLastPart = rawRuntimeVersion;
+    } else {
+      rawRuntimeVersionLastPart = rawRuntimeVersion.substring(lastUnderscore + 1);
+    }
+    try {
+      runtimeVersion = Integer.parseUnsignedInt(rawRuntimeVersionLastPart);
+    } catch (NumberFormatException ignored) {
+      // Could be e.g. the "jdk" part of "local_jdk" without a version number, which we can't
+      // check at this point.
+      return;
+    }
+
+    if (languageVersion > runtimeVersion) {
+      if (isExec) {
+        throw new InvalidConfigurationException(
+            String.format(
+                "--tool_java_language_version=%s is incompatible with current Java runtime '%s':"
+                    + " Both --tool_java_runtime_version and the 'java_runtime' attribute of the"
+                    + " Java toolchain have to be set to versions at least as high as the language"
+                    + " version.",
+                rawLanguageVersion, rawRuntimeVersion));
+      } else {
+        throw new InvalidConfigurationException(
+            String.format(
+                "--java_language_version=%s is incompatible with --java_runtime_version=%s: The"
+                    + " runtime version has to be at least as high as the language version.",
+                rawLanguageVersion, rawRuntimeVersion));
+      }
+    }
+  }
+
   @Override
   // TODO(bazel-team): this is the command-line passed options, we should remove from Starlark
   // probably.

src/test/shell/bazel/bazel_with_jdk_test.sh

@@ -289,4 +289,93 @@ function test_bazel_compiles_with_localjdk() {
   expect_not_log "exec external/remotejdk11_linux/bin/java"
 }
 
+function test_java_language_greater_than_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=17 \
+    --java_runtime_version=remotejdk_11 \
+    &>"${TEST_log}" && fail "Expected build to fail"
+
+  expect_log "--java_language_version=17 is incompatible with --java_runtime_version=remotejdk_11: The runtime version has to be at least as high as the language version."
+}
+
+function test_tool_java_language_greater_than_runtime_version() {
+  mkdir -p pkg
+  cat >pkg/BUILD <<'EOF'
+java_binary(
+    name = "Main",
+    srcs = ["Main.java"],
+    main_class = "com.example.Main",
+)
+
+genrule(
+    name = "gen",
+    outs = ["gen.txt"],
+    tools = [":Main"],
+    cmd = "$(location :Main) > $@",
+)
+EOF
+
+  cat >pkg/Main.java <<'EOF'
+package com.example;
+public class Main {
+  public static void main(String[] args) {
+    System.out.println("Hello World!");
+  }
+}
+EOF
+
+  bazel build //pkg:gen \
+    --tool_java_language_version=17 \
+    --tool_java_runtime_version=remotejdk_11 \
+    &>"${TEST_log}" && fail "Expected build to fail"
+
+  expect_log "--tool_java_language_version=17 is incompatible with current Java runtime 'remotejdk_11': Both --tool_java_runtime_version and the 'java_runtime' attribute of the Java toolchain have to be set to versions at least as high as the language version."
+}
+
+function test_tool_java_language_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",
+    deps = ["@bazel_tools//tools/java/runfiles"],
+)
+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 \
+    --tool_java_language_version=20 \
+    --tool_java_runtime_version=remotejdk_20 \
+    &>"${TEST_log}" && fail "Expected build to fail"
+
+  expect_log "--tool_java_language_version=20 is incompatible with current Java runtime 'remotejdk_17': Both --tool_java_runtime_version and the 'java_runtime' attribute of the Java toolchain have to be set to versions at least as high as the language version."
+}
+
 run_suite "Tests detection of local JDK and that Bazel executes with a bundled JDK."