From 4576e4a8a4055e3ddfe0ef1c7c10c4cb1cc7cc21 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?X=C3=B9d=C5=8Dng=20Y=C3=A1ng?= <wyverald@gmail.com>
Date: Tue, 13 Feb 2024 03:54:19 +0100
Subject: [PATCH] [7.1.0] Add `Label.to_display_form()` (#21312)

Fixes #20486

While `to_display_form()` can be called in all contexts, it only returns
apparent names for BUILD threads, which are the most common use case for
display form labels. Support for module extensions can be added later,
but requires explicit tracking of inverse mappings in the lockfile.

Also use `to_display_form()` to generate Clang module names in the
correct form for external repositories. `java_*` rules require more
delicate handling and will be migrated in a follow-up change.

RELNOTES: The `to_display_form()` method on `Label` returns a string
representation of a label optimized for readability by humans.

Closes #21179.

PiperOrigin-RevId: 606330539
Change-Id: Id6a4ad79fd3d50319320789b88c618aad28db28b

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>
---
 .../build/lib/actions/AbstractAction.java     |  10 +-
 .../build/lib/cmdline/BazelModuleContext.java |  10 +-
 .../devtools/build/lib/cmdline/Label.java     |  20 ++-
 .../build/lib/cmdline/PackageIdentifier.java  |   3 +-
 .../build/lib/cmdline/RepositoryName.java     |  11 +-
 .../build/lib/skyframe/BzlLoadFunction.java   |  35 +++++
 .../common/cc/cc_compilation_helper.bzl       |   2 +-
 .../actions/BuildInfoFileWriteActionTest.java |   1 +
 .../bzlmod/ModuleExtensionResolutionTest.java |  33 +++++
 .../devtools/build/lib/cmdline/LabelTest.java |   6 +
 .../lib/cmdline/PackageIdentifierTest.java    |   2 +
 .../build/lib/cmdline/RepositoryNameTest.java |  17 +++
 .../StarlarkRuleClassFunctionsTest.java       |   1 +
 .../util/BazelEvaluationTestCase.java         |   1 +
 src/test/py/bazel/bzlmod/bazel_module_test.py | 135 ++++++++++++++++++
 src/test/shell/bazel/BUILD                    |   1 +
 .../shell/bazel/bazel_layering_check_test.sh  |  55 +++++++
 17 files changed, 329 insertions(+), 14 deletions(-)

diff --git a/src/main/java/com/google/devtools/build/lib/actions/AbstractAction.java b/src/main/java/com/google/devtools/build/lib/actions/AbstractAction.java
index 6ea34327d30cf5..ab79b8dfdcf241 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/AbstractAction.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/AbstractAction.java
@@ -373,13 +373,9 @@ private String getProgressMessageChecked(@Nullable RepositoryMapping mainReposit
   private String replaceProgressMessagePlaceholders(
       String progressMessage, @Nullable RepositoryMapping mainRepositoryMapping) {
     if (progressMessage.contains("%{label}") && owner.getLabel() != null) {
-      String labelString;
-      if (mainRepositoryMapping != null) {
-        labelString = owner.getLabel().getDisplayForm(mainRepositoryMapping);
-      } else {
-        labelString = owner.getLabel().toString();
-      }
-      progressMessage = progressMessage.replace("%{label}", labelString);
+      progressMessage =
+          progressMessage.replace(
+              "%{label}", owner.getLabel().getDisplayForm(mainRepositoryMapping));
     }
     if (progressMessage.contains("%{output}") && getPrimaryOutput() != null) {
       progressMessage =
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/BazelModuleContext.java b/src/main/java/com/google/devtools/build/lib/cmdline/BazelModuleContext.java
index 9bd7dd45b30ef7..d5671835122135 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/BazelModuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/BazelModuleContext.java
@@ -44,6 +44,13 @@ public abstract class BazelModuleContext {
   /** The repository mapping applicable to the repo where the .bzl file is located in. */
   public abstract RepositoryMapping repoMapping();
 
+  /**
+   * The repository mapping applicable to the main repository, possibly without WORKSPACE repos or
+   * null. This is purely meant to support {@link Label#getDisplayFormForStarlark(StarlarkThread)}.
+   */
+  @Nullable
+  public abstract RepositoryMapping bestEffortMainRepoMapping();
+
   /** Returns the name of the module's .bzl file, as provided to the parser. */
   public abstract String filename();
 
@@ -160,11 +167,12 @@ public static BazelModuleContext ofInnermostBzlOrFail(StarlarkThread thread, Str
   public static BazelModuleContext create(
       Label label,
       RepositoryMapping repoMapping,
+      @Nullable RepositoryMapping bestEffortMainRepoMapping,
       String filename,
       ImmutableList<Module> loads,
       byte[] bzlTransitiveDigest) {
     return new AutoValue_BazelModuleContext(
-        label, repoMapping, filename, loads, bzlTransitiveDigest);
+        label, repoMapping, bestEffortMainRepoMapping, filename, loads, bzlTransitiveDigest);
   }
 
   public final Label.PackageContext packageContext() {
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
index a2421a278eeb04..d0de7a6897453f 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
@@ -437,10 +437,28 @@ public String getUnambiguousCanonicalForm() {
    * @param mainRepositoryMapping the {@link RepositoryMapping} of the main repository
    * @return analogous to {@link PackageIdentifier#getDisplayForm(RepositoryMapping)}
    */
-  public String getDisplayForm(RepositoryMapping mainRepositoryMapping) {
+  public String getDisplayForm(@Nullable RepositoryMapping mainRepositoryMapping) {
     return packageIdentifier.getDisplayForm(mainRepositoryMapping) + ":" + name;
   }
 
+  @StarlarkMethod(
+      name = "to_display_form",
+      useStarlarkThread = true,
+      doc =
+          "Returns a string representation of this label that is optimized for human readability."
+              + " Use this to format a <code>Label</code> for use in BUILD files. <p>The exact form"
+              + " of the return value is explicitly unspecified and subject to change. The"
+              + " following properties are guaranteed for a <code>Label</code> <code>l</code>:<ul> "
+              + " <li><code>l.to_display_form()</code> has no repository part if and only if"
+              + " <code>l</code> references the main repository;</li> "
+              + " <li><code>Label(l.to_display_form()) == l</code> if the call to"
+              + " <code>Label</code> occurs in the main repository.</li></ul>")
+  public String getDisplayFormForStarlark(StarlarkThread starlarkThread) throws EvalException {
+    checkRepoVisibilityForStarlark("to_display_form");
+    return getDisplayForm(
+        BazelModuleContext.ofInnermostBzlOrThrow(starlarkThread).bestEffortMainRepoMapping());
+  }
+
   /**
    * Returns a shorthand label string that is suitable for display, i.e. in addition to simplifying
    * the repository part, labels of the form {@code [@repo]//foo/bar:bar} are simplified to the
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index a848ba5b560a6e..79a1f8c46c047f 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -22,6 +22,7 @@
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.skyframe.SkyFunctionName;
 import com.google.devtools.build.skyframe.SkyKey;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -215,7 +216,7 @@ public String getUnambiguousCanonicalForm() {
    *       <dd>only with Bzlmod if the current package belongs to a repository that is not visible
    *           from the main module
    */
-  public String getDisplayForm(RepositoryMapping mainRepositoryMapping) {
+  public String getDisplayForm(@Nullable RepositoryMapping mainRepositoryMapping) {
     return repository.getDisplayForm(mainRepositoryMapping) + "//" + pkgName;
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
index d0b064512dd98d..984ba4ece2ac75 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
@@ -247,13 +247,15 @@ public String getCanonicalForm() {
    *       <dt><code>@protobuf</code>
    *       <dd>if this repository is a WORKSPACE dependency and its <code>name</code> is "protobuf",
    *           or if this repository is a Bzlmod dependency of the main module and its apparent name
-   *           is "protobuf"
+   *           is "protobuf" (in both cases only if mainRepositoryMapping is not null)
    *       <dt><code>@@protobuf~3.19.2</code>
    *       <dd>only with Bzlmod, if this a repository that is not visible from the main module
    */
-  public String getDisplayForm(RepositoryMapping mainRepositoryMapping) {
+  public String getDisplayForm(@Nullable RepositoryMapping mainRepositoryMapping) {
     Preconditions.checkArgument(
-        mainRepositoryMapping.ownerRepo() == null || mainRepositoryMapping.ownerRepo().isMain());
+        mainRepositoryMapping == null
+            || mainRepositoryMapping.ownerRepo() == null
+            || mainRepositoryMapping.ownerRepo().isMain());
     if (!isVisible()) {
       return getNameWithAt();
     }
@@ -261,6 +263,9 @@ public String getDisplayForm(RepositoryMapping mainRepositoryMapping) {
       // Packages in the main repository can always use repo-relative form.
       return "";
     }
+    if (mainRepositoryMapping == null) {
+      return getNameWithAt();
+    }
     if (!mainRepositoryMapping.usesStrictDeps()) {
       // If the main repository mapping is not using strict visibility, then Bzlmod is certainly
       // disabled, which means that canonical and apparent names can be used interchangeably from
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
index 048d6c252f966a..aa87501f99b0d6 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/BzlLoadFunction.java
@@ -68,6 +68,7 @@
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 import javax.annotation.Nullable;
@@ -765,6 +766,11 @@ private BzlLoadValue computeInternalWithCompiledBzl(
     if (repoMapping == null) {
       return null;
     }
+    Optional<RepositoryMapping> mainRepoMapping =
+        getMainRepositoryMapping(key, builtins.starlarkSemantics, env);
+    if (mainRepoMapping == null) {
+      return null;
+    }
     Label.RepoMappingRecorder repoMappingRecorder = new Label.RepoMappingRecorder();
     ImmutableList<Pair<String, Location>> programLoads = getLoadsFromProgram(prog);
     ImmutableList<Label> loadLabels =
@@ -843,6 +849,7 @@ private BzlLoadValue computeInternalWithCompiledBzl(
         BazelModuleContext.create(
             label,
             repoMapping,
+            mainRepoMapping.orElse(null),
             prog.getFilename(),
             ImmutableList.copyOf(loadMap.values()),
             transitiveDigest);
@@ -977,6 +984,34 @@ private static RepositoryMapping getRepositoryMapping(
     return repositoryMappingValue.getRepositoryMapping();
   }
 
+  @Nullable
+  private static Optional<RepositoryMapping> getMainRepositoryMapping(
+      BzlLoadValue.Key key, StarlarkSemantics starlarkSemantics, Environment env)
+      throws InterruptedException {
+    if (!starlarkSemantics.getBool(BuildLanguageOptions.ENABLE_BZLMOD)) {
+      return Optional.empty();
+    }
+    RepositoryMappingValue.Key repoMappingKey;
+    // When adding cases for other key types such as WORKSPACE or Bzlmod, make sure to track the
+    // usages of the repo mapping in persistent caches, such as repository marker files and the
+    // MODULE.bazel.lock file.
+    if (key instanceof BzlLoadValue.KeyForBuild) {
+      repoMappingKey = RepositoryMappingValue.key(RepositoryName.MAIN);
+    } else if (key instanceof BzlLoadValue.KeyForBuiltins) {
+      // Using the full main repo mapping here results in a cycle as it depends on WORKSPACE, but
+      // builtins are injected into WORKSPACE. Fixing this fully would require adding a new key type
+      // for builtins (transitively) loaded from WORKSPACE.
+      repoMappingKey = RepositoryMappingValue.KEY_FOR_ROOT_MODULE_WITHOUT_WORKSPACE_REPOS;
+    } else {
+      return Optional.empty();
+    }
+    var mainRepositoryMappingValue = (RepositoryMappingValue) env.getValue(repoMappingKey);
+    if (mainRepositoryMappingValue == null) {
+      return null;
+    }
+    return Optional.of(mainRepositoryMappingValue.getRepositoryMapping());
+  }
+
   /**
    * Validates a label appearing in a {@code load()} statement, throwing {@link
    * LabelSyntaxException} on failure.
diff --git a/src/main/starlark/builtins_bzl/common/cc/cc_compilation_helper.bzl b/src/main/starlark/builtins_bzl/common/cc/cc_compilation_helper.bzl
index 1177edbbd71630..bca2fa56c0b102 100644
--- a/src/main/starlark/builtins_bzl/common/cc/cc_compilation_helper.bzl
+++ b/src/main/starlark/builtins_bzl/common/cc/cc_compilation_helper.bzl
@@ -297,7 +297,7 @@ def _init_cc_compilation_context(
         if not module_map:
             module_map = cc_common.create_module_map(
                 file = actions.declare_file(label.name + ".cppmap"),
-                name = label.workspace_name + "//" + label.package + ":" + label.name,
+                name = label.to_display_form(),
             )
 
         # There are different modes for module compilation:
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/actions/BuildInfoFileWriteActionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/actions/BuildInfoFileWriteActionTest.java
index 507da64e3c9882..c733a16b4bf7ea 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/actions/BuildInfoFileWriteActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/actions/BuildInfoFileWriteActionTest.java
@@ -78,6 +78,7 @@ private static Object exec(String... lines) throws Exception {
               BazelModuleContext.create(
                   Label.parseCanonicalUnchecked("//test:label"),
                   RepositoryMapping.ALWAYS_FALLBACK,
+                  /* bestEffortMainRepoMapping= */ null,
                   "test/label.bzl",
                   /* loads= */ ImmutableList.of(),
                   /* bzlTransitiveDigest= */ new byte[0])),
diff --git a/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleExtensionResolutionTest.java b/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleExtensionResolutionTest.java
index b02b67ac773e3b..5e662c559a06b8 100644
--- a/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleExtensionResolutionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleExtensionResolutionTest.java
@@ -2533,4 +2533,37 @@ public void innate_noSuchValue() throws Exception {
             "//:repo.bzl does not export a repository_rule called data_repo, yet its use is"
                 + " requested at /ws/MODULE.bazel");
   }
+
+  @Test
+  public void labelToDisplayForm() throws Exception {
+    scratch.file(
+        workspaceRoot.getRelative("MODULE.bazel").getPathString(),
+        "bazel_dep(name='data_repo', version='1.0')",
+        "ext = use_extension('//:defs.bzl', 'ext')",
+        "use_repo(ext, 'foo', 'bar', 'baz')");
+    scratch.file(
+        workspaceRoot.getRelative("defs.bzl").getPathString(),
+        "load('@data_repo//:defs.bzl','data_repo')",
+        "def _ext_impl(ctx):",
+        "  data_repo(name='foo',data=Label('//:foo').to_display_form())",
+        "  data_repo(name='bar',data=Label('@data_repo//:bar').to_display_form())",
+        "  data_repo(name='baz',data=Label('@@canonical_name//:baz').to_display_form())",
+        "ext = module_extension(implementation=_ext_impl)");
+    scratch.file(workspaceRoot.getRelative("BUILD").getPathString());
+    scratch.file(
+        workspaceRoot.getRelative("data.bzl").getPathString(),
+        "load('@foo//:data.bzl', foo_data='data')",
+        "load('@bar//:data.bzl', bar_data='data')",
+        "load('@baz//:data.bzl', baz_data='data')",
+        "data = 'foo:'+foo_data+' bar:'+bar_data+' baz:'+baz_data");
+
+    SkyKey skyKey = BzlLoadValue.keyForBuild(Label.parseCanonical("//:data.bzl"));
+    EvaluationResult<BzlLoadValue> result =
+        evaluator.evaluate(ImmutableList.of(skyKey), evaluationContext);
+    if (result.hasError()) {
+      throw result.getError().getException();
+    }
+    assertThat(result.get(skyKey).getModule().getGlobal("data"))
+        .isEqualTo("foo://:foo bar:@@data_repo~//:bar baz:@@canonical_name//:baz");
+  }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java b/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
index a31d185cc8d8ee..7b86935cdbd1ee 100644
--- a/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
+++ b/src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java
@@ -418,6 +418,12 @@ public void testDisplayForm() throws Exception {
         .isEqualTo("@unremapped//:unremapped");
   }
 
+  @Test
+  public void testDisplayFormNullMapping() throws Exception {
+    assertThat(displayFormFor("//foo/bar:bar", null)).isEqualTo("//foo/bar:bar");
+    assertThat(displayFormFor("@@foo//bar:bar", null)).isEqualTo("@@foo//bar:bar");
+  }
+
   private static String shorthandDisplayFormFor(
       String rawLabel, RepositoryMapping repositoryMapping) throws Exception {
     return Label.parseCanonical(rawLabel).getShorthandDisplayForm(repositoryMapping);
diff --git a/src/test/java/com/google/devtools/build/lib/cmdline/PackageIdentifierTest.java b/src/test/java/com/google/devtools/build/lib/cmdline/PackageIdentifierTest.java
index 07f025f3f2c9bf..3336ed90524029 100644
--- a/src/test/java/com/google/devtools/build/lib/cmdline/PackageIdentifierTest.java
+++ b/src/test/java/com/google/devtools/build/lib/cmdline/PackageIdentifierTest.java
@@ -120,6 +120,7 @@ public void testDisplayFormInMainRepository() throws Exception {
                 RepositoryMapping.create(
                     ImmutableMap.of("foo", RepositoryName.create("bar")), RepositoryName.MAIN)))
         .isEqualTo("//some/pkg");
+    assertThat(pkg.getDisplayForm(null)).isEqualTo("//some/pkg");
   }
 
   @Test
@@ -139,5 +140,6 @@ public void testDisplayFormInExternalRepository() throws Exception {
                     ImmutableMap.of("local", RepositoryName.create("other_repo")),
                     RepositoryName.MAIN)))
         .isEqualTo("@@canonical//some/pkg");
+    assertThat(pkg.getDisplayForm(null)).isEqualTo("@@canonical//some/pkg");
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java b/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
index 482f2d2e779c52..71cb12ac7efb62 100644
--- a/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
+++ b/src/test/java/com/google/devtools/build/lib/cmdline/RepositoryNameTest.java
@@ -105,4 +105,21 @@ public void testGetDisplayForm() throws Exception {
                 .getDisplayForm(repositoryMapping))
         .isEqualTo("@@[unknown repo 'local' requested from @@owner]");
   }
+
+  @Test
+  public void testGetDisplayFormWithNullMapping() throws Exception {
+    assertThat(RepositoryName.create("").getDisplayForm(null)).isEmpty();
+    assertThat(RepositoryName.create("canonical").getDisplayForm(null)).isEqualTo("@@canonical");
+
+    assertThat(
+            RepositoryName.create("")
+                .toNonVisible(RepositoryName.create("owner"))
+                .getDisplayForm(null))
+        .isEqualTo("@@[unknown repo '' requested from @@owner]");
+    assertThat(
+            RepositoryName.create("canonical")
+                .toNonVisible(RepositoryName.create("owner"))
+                .getDisplayForm(null))
+        .isEqualTo("@@[unknown repo 'canonical' requested from @@owner]");
+  }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
index 1ced7947625c11..848d5ae49d4c68 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
@@ -4824,6 +4824,7 @@ public void testLabelWithStrictVisibility() throws Exception {
             bzlLabel,
             RepositoryMapping.create(
                 ImmutableMap.of("my_module", currentRepo, "dep", otherRepo), currentRepo),
+            /* bestEffortMainRepoMapping= */ null,
             "lib/label.bzl",
             /* loads= */ ImmutableList.of(),
             /* bzlTransitiveDigest= */ new byte[0]);
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/util/BazelEvaluationTestCase.java b/src/test/java/com/google/devtools/build/lib/starlark/util/BazelEvaluationTestCase.java
index b32649fc8033c6..0cdf1657ce1193 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/util/BazelEvaluationTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/starlark/util/BazelEvaluationTestCase.java
@@ -175,6 +175,7 @@ private Object newModule(ImmutableMap.Builder<String, Object> predeclared) {
     return BazelModuleContext.create(
         label,
         RepositoryMapping.ALWAYS_FALLBACK,
+        /* bestEffortMainRepoMapping= */ null,
         "test/label.bzl",
         /* loads= */ ImmutableList.of(),
         /* bzlTransitiveDigest= */ new byte[0]);
diff --git a/src/test/py/bazel/bzlmod/bazel_module_test.py b/src/test/py/bazel/bzlmod/bazel_module_test.py
index 068f6c6da85a71..55dfee62359daf 100644
--- a/src/test/py/bazel/bzlmod/bazel_module_test.py
+++ b/src/test/py/bazel/bzlmod/bazel_module_test.py
@@ -844,6 +844,141 @@ def testHttpJar(self):
 
     self.RunBazel(['build', '@my_jar//jar'])
 
+  def testLabelToDisplayForm(self):
+    self.main_registry.setModuleBasePath('projects')
+    projects_dir = self.main_registry.projects
+
+    self.ScratchFile(
+        'MODULE.bazel',
+        [
+            'module(name="root",version="0.1")',
+            'bazel_dep(name="foo",version="1.0")',
+            'ext = use_extension("@foo//:ext.bzl", "ext")',
+            'use_repo(ext, "ext_repo")',
+        ],
+    )
+    self.ScratchFile(
+        'WORKSPACE.bzlmod',
+        [
+            'local_repository(name="quux",path="quux")',
+            'load("@foo//:ext.bzl", "ext_repo")',
+            'ext_repo(name="workspace_repo")',
+        ],
+    )
+    self.ScratchFile(
+        'BUILD',
+        [
+            'load("@foo//:defs.bzl", "my_macro", "my_rule")',
+            'my_macro(name="main_macro")',
+            'my_rule(name="main_rule")',
+        ],
+    )
+    self.main_registry.createLocalPathModule('foo', '1.0', 'foo')
+    scratchFile(
+        projects_dir.joinpath('foo', 'BUILD'),
+        [
+            'load(":defs.bzl", "my_macro", "my_rule")',
+            'my_macro(name="foo_macro")',
+            'my_rule(name="foo_rule")',
+        ],
+    )
+    scratchFile(
+        projects_dir.joinpath('foo', 'defs.bzl'),
+        [
+            'print("init => " + Label("@foo//:init").to_display_form())',
+            'def my_macro(name):',
+            '  label = native.package_relative_label(name)',
+            '  print(name + " => " + label.to_display_form())',
+            '',
+            'def _my_rule(ctx):',
+            '  print(ctx.attr.name + " => " + ctx.label.to_display_form())',
+            '  out = ctx.actions.declare_file(ctx.attr.name)',
+            '  ctx.actions.write(out, "")',
+            '  return [DefaultInfo(files = depset([out]))]',
+            'my_rule = rule(implementation = _my_rule)',
+        ],
+    )
+    scratchFile(
+        projects_dir.joinpath('foo', 'ext.bzl'),
+        [
+            'def _ext_repo(rctx):',
+            '  name = rctx.attr.name',
+            '  if "~" in name:',
+            '    name = name.rpartition("~")[-1]',
+            (
+                '  print(name + "_impl => " +'
+                ' Label("@foo//:repo_impl").to_display_form())'
+            ),
+            '  rctx.file("BUILD",',
+            (
+                '    ("load(\\"@foo//:defs.bzl\\", \\"my_macro\\",'
+                ' \\"my_rule\\")\\n" +'
+            ),
+            '    "my_macro(name=\\"{name}_macro\\")\\n" +',
+            '    "my_rule(name=\\"{name}_rule\\")").format(name = str(name)))',
+            'ext_repo = repository_rule(_ext_repo)',
+            'def _ext(mctx):',
+            (
+                '  print("ext_impl => " +'
+                ' Label("@foo//:ext_impl").to_display_form())'
+            ),
+            '  ext_repo(name="ext_repo")',
+            'ext = module_extension(_ext)',
+        ],
+    )
+
+    self.ScratchFile('quux/REPO.bazel')
+    self.ScratchFile(
+        'quux/BUILD',
+        [
+            'load("@foo//:defs.bzl", "my_macro", "my_rule")',
+            'my_macro(name="quux_macro")',
+            'my_rule(name="quux_rule")',
+        ],
+    )
+
+    _, _, stderr = self.RunBazel(
+        [
+            'build',
+            '--enable_workspace',
+            '//:all',
+            '@foo//:all',
+            '@ext_repo//:all',
+            '@quux//:all',
+            '@workspace_repo//:all',
+        ],
+    )
+    stderr = '\n'.join(stderr)
+
+    # Display form of labels in global constants uses apparent names.
+    self.assertIn('init => @foo//:init', stderr)
+
+    # Display form of labels in rule implementation functions uses
+    # apparent names.
+    self.assertIn('main_rule => //:main_rule', stderr)
+    self.assertIn('foo_rule => @foo//:foo_rule', stderr)
+    self.assertIn('ext_repo_rule => @ext_repo//:ext_repo_rule', stderr)
+    self.assertIn('quux_rule => @quux//:quux_rule', stderr)
+    self.assertIn(
+        'workspace_repo_rule => @workspace_repo//:workspace_repo_rule', stderr
+    )
+
+    # Display form of labels in macros uses apparent names.
+    self.assertIn('main_macro => //:main_macro', stderr)
+    self.assertIn('foo_macro => @foo//:foo_macro', stderr)
+    self.assertIn('ext_repo_macro => @ext_repo//:ext_repo_macro', stderr)
+    self.assertIn('quux_macro => @quux//:quux_macro', stderr)
+    self.assertIn(
+        'workspace_repo_macro => @workspace_repo//:workspace_repo_macro', stderr
+    )
+
+    # Display form of labels in extensions uses canonical names.
+    self.assertIn('ext_impl => @@foo~//:ext_impl', stderr)
+    self.assertIn('ext_repo_impl => @@foo~//:repo_impl', stderr)
+
+    # Display form of labels in WORKSPACE loaded files uses canonical names.
+    self.assertIn('workspace_repo_impl => @@foo~//:repo_impl', stderr)
+
 
 if __name__ == '__main__':
   absltest.main()
diff --git a/src/test/shell/bazel/BUILD b/src/test/shell/bazel/BUILD
index 30e11972eef88e..9d0c4e92d81442 100644
--- a/src/test/shell/bazel/BUILD
+++ b/src/test/shell/bazel/BUILD
@@ -634,6 +634,7 @@ sh_test(
     data = [":test-deps"],
     tags = [
         "no_windows",
+        "requires-network",  # Allow this test to access the BCR
     ],
 )
 
diff --git a/src/test/shell/bazel/bazel_layering_check_test.sh b/src/test/shell/bazel/bazel_layering_check_test.sh
index 4942f462944e99..7a7d06578dc062 100755
--- a/src/test/shell/bazel/bazel_layering_check_test.sh
+++ b/src/test/shell/bazel/bazel_layering_check_test.sh
@@ -167,4 +167,59 @@ function test_bazel_layering_check() {
     "'base.h'"
 }
 
+function test_bazel_layering_check_external_repo() {
+  if is_darwin; then
+    echo "This test doesn't run on Darwin. Skipping."
+    return
+  fi
+
+  local -r clang_tool=$(which clang)
+  if [[ ! -x ${clang_tool:-/usr/bin/clang_tool} ]]; then
+    echo "clang not installed. Skipping test."
+    return
+  fi
+
+  cat << 'EOF' > MODULE.bazel
+bazel_dep(
+    name = "lib",
+    repo_name = "my_lib",
+)
+local_path_override(
+    module_name = "lib",
+    path = "lib",
+)
+EOF
+
+  mkdir -p lib
+  cat << 'EOF' > lib/MODULE.bazel
+module(name = "lib")
+EOF
+  mkdir -p lib/pkg
+  cat << 'EOF' > lib/pkg/BUILD
+cc_library(name = "a", srcs = ["a.cc"], deps = [":b"])
+cc_library(name = "b", srcs = ["b.cc"], hdrs = ["b.h"], deps = [":c"])
+cc_library(name = "c", srcs = ["c.cc"], hdrs = ["c.h"])
+EOF
+  cat << 'EOF' > lib/pkg/a.cc
+#include "b.h"
+#include "c.h"
+EOF
+  cat << 'EOF' > lib/pkg/b.cc
+#include "b.h"
+#include "c.h"
+EOF
+  cat << 'EOF' > lib/pkg/b.h
+#include "c.h"
+EOF
+  cat << 'EOF' > lib/pkg/c.cc
+#include "c.h"
+EOF
+  touch lib/pkg/c.h
+
+  CC="${clang_tool}" bazel build @my_lib//pkg:a --features=layering_check \
+    -s \
+    &> $TEST_log && fail "Build should have failed"
+  expect_log "module @my_lib//pkg:a does not depend on a module exporting 'c.h'"
+}
+
 run_suite "test layering_check"