Improve use_repo_rule error when not referencing a repository_rule

Makes the error message less confusing when referencing an existing symbol that happens to be a macro, not a repository rule.

Closes #20657.

PiperOrigin-RevId: 595434847
Change-Id: Ifc37a65685c0196301d79a439f3245037cf39e21

src/main/java/com/google/devtools/build/lib/bazel/bzlmod/SingleExtensionEvalFunction.java

@@ -620,7 +620,7 @@ public RunModuleExtensionResult run(
  // Instiantiate the repos one by one.
  for (InnateExtensionRepo repo : repos) {
  Object exported = repo.loadedBzl().getModule().getGlobal(repo.ruleName());
- if (!(exported instanceof RepositoryRuleFunction)) {
+ if (exported == null) {
  ImmutableSet<String> exportedRepoRules =
  repo.loadedBzl().getModule().getGlobals().entrySet().stream()
  .filter(e -> e.getValue() instanceof RepositoryRuleFunction)
@@ -636,6 +636,17 @@ public RunModuleExtensionResult run(
  repo.tag().getLocation(),
  SpellChecker.didYouMean(repo.ruleName(), exportedRepoRules)),
  Transience.PERSISTENT);
+ } else if (!(exported instanceof RepositoryRuleFunction)) {
+ throw new SingleExtensionEvalFunctionException(
+ ExternalDepsException.withMessage(
+ Code.BAD_MODULE,
+ "%s exports a value called %s of type %s, yet a repository_rule is requested"
+ + " at %s",
+ repo.bzlLabel(),
+ repo.ruleName(),
+ Starlark.type(exported),
+ repo.tag().getLocation()),
+ Transience.PERSISTENT);
  }
  RepositoryRuleFunction repoRule = (RepositoryRuleFunction) exported;
  Dict<String, Object> kwargs = repo.tag().getAttributeValues().attributes();

src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleExtensionResolutionTest.java

@@ -2453,7 +2453,35 @@ public void innate_noSuchRepoRule() throws Exception {
  "load('@data//:data.bzl', self_data='data')",
  "data=self_data");
  scratch.file(
- workspaceRoot.getRelative("repo.bzl").getPathString(), "data_repo = 3 # not a repo rule");
+ workspaceRoot.getRelative("repo.bzl").getPathString(),
+ "# not a repo rule",
+ "def data_repo(name):",
+ " pass");
+
+ SkyKey skyKey = BzlLoadValue.keyForBuild(Label.parseCanonical("//:data.bzl"));
+ reporter.removeHandler(failFastHandler);
+ EvaluationResult<BzlLoadValue> result =
+ evaluator.evaluate(ImmutableList.of(skyKey), evaluationContext);
+ assertThat(result.hasError()).isTrue();
+ assertThat(result.getError().getException())
+ .hasMessageThat()
+ .contains(
+ "//:repo.bzl exports a value called data_repo of type function, yet a repository_rule"
+ + " is requested at /ws/MODULE.bazel");
+ }
+
+ @Test
+ public void innate_noSuchValue() throws Exception {
+ scratch.file(
+ workspaceRoot.getRelative("MODULE.bazel").getPathString(),
+ "data_repo = use_repo_rule('//:repo.bzl', 'data_repo')",
+ "data_repo(name='data', data='get up at 6am.')");
+ scratch.file(workspaceRoot.getRelative("BUILD").getPathString());
+ scratch.file(
+ workspaceRoot.getRelative("data.bzl").getPathString(),
+ "load('@data//:data.bzl', self_data='data')",
+ "data=self_data");
+ scratch.file(workspaceRoot.getRelative("repo.bzl").getPathString(), "");
 
  SkyKey skyKey = BzlLoadValue.keyForBuild(Label.parseCanonical("//:data.bzl"));
  reporter.removeHandler(failFastHandler);