Add a flag to enable unambiguous stringification of Labels

Work towards #15916

RELNOTES[INC]: Added a new flag --incompatible_unambiguous_label_stringification, which causes labels in the main repo to stringify into unambiguous forms starting with an @. See #15916 for more information.

PiperOrigin-RevId: 466346190
Change-Id: I302b8893d35a3eae7795754f7b5c1ac3839bb519

src/main/java/com/google/devtools/build/lib/cmdline/Label.java

@@ -613,18 +613,24 @@ public boolean isImmutable() {
 
   @Override
   public void repr(Printer printer) {
+    // TODO(wyv): Consider using StarlarkSemantics here too for optional unambiguity.
     printer.append("Label(");
     printer.repr(getCanonicalForm());
     printer.append(")");
   }
 
   @Override
   public void str(Printer printer, StarlarkSemantics semantics) {
-    printer.append(getCanonicalForm());
+    if (semantics.getBool(BuildLanguageOptions.INCOMPATIBLE_UNAMBIGUOUS_LABEL_STRINGIFICATION)) {
+      printer.append(getUnambiguousCanonicalForm());
+    } else {
+      printer.append(getCanonicalForm());
+    }
   }
 
   @Override
   public String expandToCommandLine() {
+    // TODO(wyv): Consider using StarlarkSemantics here too for optional unambiguity.
     return getCanonicalForm();
   }
 }

src/main/java/com/google/devtools/build/lib/packages/semantics/BuildLanguageOptions.java

@@ -518,6 +518,19 @@ public final class BuildLanguageOptions extends OptionsBase {
               + "migration instructions.")
   public boolean incompatibleUseCcConfigureFromRulesCc;
 
+  @Option(
+      name = "incompatible_unambiguous_label_stringification",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
+      effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
+      metadataTags = {OptionMetadataTag.INCOMPATIBLE_CHANGE},
+      help =
+          "When true, Bazel will stringify the label @//foo:bar to @//foo:bar, instead of"
+              + " //foo:bar. This only affects the behavior of str(), the % operator, and so on;"
+              + " the behavior of repr() is unchanged. See"
+              + " https://github.com/bazelbuild/bazel/issues/15916 for more information.")
+  public boolean incompatibleUnambiguousLabelStringification;
+
   @Option(
       name = "incompatible_depset_for_libraries_to_link_getter",
       defaultValue = "true",
@@ -667,6 +680,9 @@ public StarlarkSemantics toStarlarkSemantics() {
                 INCOMPATIBLE_DO_NOT_SPLIT_LINKING_CMDLINE, incompatibleDoNotSplitLinkingCmdline)
             .setBool(
                 INCOMPATIBLE_USE_CC_CONFIGURE_FROM_RULES_CC, incompatibleUseCcConfigureFromRulesCc)
+            .setBool(
+                INCOMPATIBLE_UNAMBIGUOUS_LABEL_STRINGIFICATION,
+                incompatibleUnambiguousLabelStringification)
             .setBool(
                 INCOMPATIBLE_DEPSET_FOR_LIBRARIES_TO_LINK_GETTER,
                 incompatibleDepsetForLibrariesToLinkGetter)
@@ -751,6 +767,8 @@ public StarlarkSemantics toStarlarkSemantics() {
       "-incompatible_struct_has_no_methods";
   public static final String INCOMPATIBLE_USE_CC_CONFIGURE_FROM_RULES_CC =
       "-incompatible_use_cc_configure_from_rules";
+  public static final String INCOMPATIBLE_UNAMBIGUOUS_LABEL_STRINGIFICATION =
+      "-incompatible_unambiguous_label_stringification";
   public static final String INCOMPATIBLE_VISIBILITY_PRIVATE_ATTRIBUTES_AT_DEFINITION =
       "-incompatible_visibility_private_attributes_at_definition";
   public static final String INCOMPATIBLE_TOP_LEVEL_ASPECTS_REQUIRE_PROVIDERS =

src/test/java/com/google/devtools/build/lib/cmdline/BUILD

@@ -22,6 +22,7 @@ java_library(
         "//src/main/java/com/google/devtools/build/lib/cmdline:parallel_visitor",
         "//src/main/java/com/google/devtools/build/lib/cmdline:query_exception_marker_interface",
         "//src/main/java/com/google/devtools/build/lib/concurrent",
+        "//src/main/java/com/google/devtools/build/lib/packages/semantics",
         "//src/main/java/com/google/devtools/build/lib/vfs:pathfragment",
         "//src/main/java/net/starlark/java/eval",
         "//src/test/java/com/google/devtools/build/lib/testutil:TestThread",

src/test/java/com/google/devtools/build/lib/cmdline/LabelTest.java

@@ -18,6 +18,7 @@
 
 import com.google.common.collect.ImmutableMap;
 import com.google.common.testing.EqualsTester;
+import com.google.devtools.build.lib.packages.semantics.BuildLanguageOptions;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import java.util.regex.Pattern;
 import net.starlark.java.eval.Starlark;
@@ -429,4 +430,14 @@ public void testStarlarkStrAndRepr() throws Exception {
     assertThat(Starlark.str(label, StarlarkSemantics.DEFAULT)).isEqualTo("//x:x");
     assertThat(Starlark.repr(label)).isEqualTo("Label(\"//x:x\")");
   }
+
+  @Test
+  public void testStarlarkStr_unambiguous() throws Exception {
+    Label label = Label.parseCanonical("//x");
+    StarlarkSemantics semantics =
+        StarlarkSemantics.builder()
+            .setBool(BuildLanguageOptions.INCOMPATIBLE_UNAMBIGUOUS_LABEL_STRINGIFICATION, true)
+            .build();
+    assertThat(Starlark.str(label, semantics)).isEqualTo("@//x:x");
+  }
 }

src/test/java/com/google/devtools/build/lib/packages/semantics/ConsistencyTest.java

@@ -151,6 +151,7 @@ private static BuildLanguageOptions buildRandomOptions(Random rand) throws Excep
         "--incompatible_visibility_private_attributes_at_definition=" + rand.nextBoolean(),
         "--incompatible_require_linker_input_cc_api=" + rand.nextBoolean(),
         "--incompatible_use_cc_configure_from_rules_cc=" + rand.nextBoolean(),
+        "--incompatible_unambiguous_label_stringification=" + rand.nextBoolean(),
         "--internal_starlark_flag_test_canary=" + rand.nextBoolean(),
         "--max_computation_steps=" + rand.nextLong());
   }
@@ -205,6 +206,8 @@ private static StarlarkSemantics buildRandomSemantics(Random rand) {
         .setBool(BuildLanguageOptions.INCOMPATIBLE_REQUIRE_LINKER_INPUT_CC_API, rand.nextBoolean())
         .setBool(
             BuildLanguageOptions.INCOMPATIBLE_USE_CC_CONFIGURE_FROM_RULES_CC, rand.nextBoolean())
+        .setBool(
+            BuildLanguageOptions.INCOMPATIBLE_UNAMBIGUOUS_LABEL_STRINGIFICATION, rand.nextBoolean())
         .setBool(StarlarkSemantics.PRINT_TEST_MARKER, rand.nextBoolean())
         .set(BuildLanguageOptions.MAX_COMPUTATION_STEPS, rand.nextLong())
         .build();