[6.3.0] Handle exception instead of crashing

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

@@ -771,9 +771,15 @@ public String getName() {
  public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwargs)
  throws EvalException, InterruptedException {
  if (!args.isEmpty()) {
- throw new EvalException("unexpected positional arguments");
+ throw new EvalException("Unexpected positional arguments");
+ }
+ try {
+ BazelStarlarkContext.from(thread).checkLoadingPhase(getName());
+ } catch (IllegalStateException e) {
+ throw new EvalException(
+ "A rule can only be instantiated in a BUILD file, or a macro "
+ + "invoked from a BUILD file");
  }
- BazelStarlarkContext.from(thread).checkLoadingPhase(getName());
  if (ruleClass == null) {
  throw new EvalException("Invalid rule class hasn't been exported by a bzl file");
  }

src/test/py/bazel/bzlmod/bazel_module_test.py

@@ -635,6 +635,37 @@ def testWorkspaceToolchainRegistrationWithPlatformsConstraint(self):
  with open(self.Path('bazel-bin/my_consumer'), 'r') as f:
  self.assertEqual(f.read().strip(), 'my_value = Hello, Bzlmod!')
 
+ def testModuleExtensionWithRuleError(self):
+ self.ScratchFile(
+ 'MODULE.bazel',
+ [
+ 'ext = use_extension("extensions.bzl", "ext")',
+ 'use_repo(ext, "ext")',
+ ],
+ )
+ self.ScratchFile('BUILD')
+ self.ScratchFile(
+ 'extensions.bzl',
+ [
+ 'def _rule_impl(ctx):',
+ ' print("RULE CALLED")',
+ 'init_rule = rule(_rule_impl)',
+ 'def ext_impl(module_ctx):',
+ ' init_rule()',
+ 'ext = module_extension(implementation = ext_impl,)',
+ ],
+ )
+ exit_code, _, stderr = self.RunBazel(
+ ['build', '--nobuild', '@ext//:all'],
+ allow_failure=True,
+ )
+ self.AssertExitCode(exit_code, 48, stderr)
+ self.assertIn(
+ 'Error in init_rule: A rule can only be instantiated in a BUILD file, '
+ 'or a macro invoked from a BUILD file',
+ stderr,
+ )
+
 
 if __name__ == '__main__':
  unittest.main()