Disallow rule implementation functions to return a struct

Such functions should return a list of providers instead.
This change represents a deprecation of the "old" syntax.

This is an incompatible change attached to new flag --incompatible_disallow_struct_provider_syntax.

See https://docs.google.com/document/d/14A9HK8Jn2jErMayLEE3nrNJIxNfZWN_slFbhgtS6-aM for details.

Migration tracker: #7347
Progress toward #6241

RELNOTES: New incompatible flag --incompatible_disallow_struct_provider_syntax removes the ability for rule implementation functions to return struct. Such functions should return a list of providers instead. Migration tracking: #7347
PiperOrigin-RevId: 232547460

src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkRuleConfiguredTargetUtil.java

@@ -318,6 +318,16 @@ private static void addProviders(
       // Use the creation location of this struct as a better reference in error messages
       loc = info.getCreationLoc();
       if (info.getProvider().getKey().equals(StructProvider.STRUCT.getKey())) {
+
+        if (context.getSkylarkSemantics().incompatibleDisallowStructProviderSyntax()) {
+          throw new EvalException(
+              loc,
+              "Returning a struct from a rule implementation function is deprecated and will "
+                  + "be removed soon. It may be temporarily re-enabled by setting "
+                  + "--incompatible_disallow_struct_provider_syntax=false . See "
+                  + "https://github.com/bazelbuild/bazel/issues/7347 for details.");
+        }
+
         // Old-style struct, but it may contain declared providers
         StructImpl struct = (StructImpl) target;
         oldStyleProviders = struct;

src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java

@@ -325,6 +325,20 @@ public class SkylarkSemanticsOptions extends OptionsBase implements Serializable
   )
   public boolean incompatibleDisallowLoadLabelsToCrossPackageBoundaries;
 
+  @Option(
+      name = "incompatible_disallow_struct_provider_syntax",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.SKYLARK_SEMANTICS,
+      effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
+      metadataTags = {
+        OptionMetadataTag.INCOMPATIBLE_CHANGE,
+        OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES
+      },
+      help =
+          "If set to true, rule implementation functions may not return a struct. They must "
+              + "instead return a list of provider instances.")
+  public boolean incompatibleDisallowStructProviderSyntax;
+
   @Option(
       name = "incompatible_generate_javacommon_source_jar",
       defaultValue = "true",
@@ -555,6 +569,7 @@ public SkylarkSemantics toSkylarkSemantics() {
         .incompatibleDisallowLoadLabelsToCrossPackageBoundaries(
             incompatibleDisallowLoadLabelsToCrossPackageBoundaries)
         .incompatibleDisallowOldStyleArgsAdd(incompatibleDisallowOldStyleArgsAdd)
+        .incompatibleDisallowStructProviderSyntax(incompatibleDisallowStructProviderSyntax)
         .incompatibleExpandDirectories(incompatibleExpandDirectories)
         .incompatibleGenerateJavaCommonSourceJar(incompatibleGenerateJavaCommonSourceJar)
         .incompatibleNewActionsApi(incompatibleNewActionsApi)

src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java

@@ -158,6 +158,8 @@ public boolean flagValue(FlagIdentifier flagIdentifier) {
 
   public abstract boolean incompatibleDisallowOldStyleArgsAdd();
 
+  public abstract boolean incompatibleDisallowStructProviderSyntax();
+
   public abstract boolean incompatibleExpandDirectories();
 
   public abstract boolean incompatibleGenerateJavaCommonSourceJar();
@@ -225,6 +227,7 @@ public static Builder builderWithDefaults() {
           .incompatibleDisallowLegacyJavaInfo(false)
           .incompatibleDisallowLoadLabelsToCrossPackageBoundaries(false)
           .incompatibleDisallowOldStyleArgsAdd(false)
+          .incompatibleDisallowStructProviderSyntax(false)
           .incompatibleExpandDirectories(true)
           .incompatibleGenerateJavaCommonSourceJar(true)
           .incompatibleNewActionsApi(false)
@@ -290,6 +293,8 @@ public abstract static class Builder {
 
     public abstract Builder incompatibleDisallowOldStyleArgsAdd(boolean value);
 
+    public abstract Builder incompatibleDisallowStructProviderSyntax(boolean value);
+
     public abstract Builder incompatibleExpandDirectories(boolean value);
 
     public abstract Builder incompatibleGenerateJavaCommonSourceJar(boolean value);

src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java

@@ -145,6 +145,7 @@ private static SkylarkSemanticsOptions buildRandomOptions(Random rand) throws Ex
         "--incompatible_disallow_legacy_java_provider=" + rand.nextBoolean(),
         "--incompatible_disallow_load_labels_to_cross_package_boundaries=" + rand.nextBoolean(),
         "--incompatible_disallow_old_style_args_add=" + rand.nextBoolean(),
+        "--incompatible_disallow_struct_provider_syntax=" + rand.nextBoolean(),
         "--incompatible_expand_directories=" + rand.nextBoolean(),
         "--incompatible_generate_javacommon_source_jar=" + rand.nextBoolean(),
         "--incompatible_new_actions_api=" + rand.nextBoolean(),
@@ -192,6 +193,7 @@ private static SkylarkSemantics buildRandomSemantics(Random rand) {
         .incompatibleDisallowLegacyJavaProvider(rand.nextBoolean())
         .incompatibleDisallowLoadLabelsToCrossPackageBoundaries(rand.nextBoolean())
         .incompatibleDisallowOldStyleArgsAdd(rand.nextBoolean())
+        .incompatibleDisallowStructProviderSyntax(rand.nextBoolean())
         .incompatibleExpandDirectories(rand.nextBoolean())
         .incompatibleGenerateJavaCommonSourceJar(rand.nextBoolean())
         .incompatibleNewActionsApi(rand.nextBoolean())

src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java

@@ -2749,6 +2749,29 @@ public void testLicenseType() throws Exception {
     assertContainsEvent("<license object>");
   }
 
+  @Test
+  public void testDisallowStructProviderSyntax() throws Exception {
+    setSkylarkSemanticsOptions("--incompatible_disallow_struct_provider_syntax=true");
+    scratch.file(
+        "test/skylark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  return struct()",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl)");
+    scratch.file(
+        "test/skylark/BUILD",
+        "load('//test/skylark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')");
+
+    reporter.removeHandler(failFastHandler);
+    getConfiguredTarget("//test/skylark:cr");
+    assertContainsEvent(
+        "Returning a struct from a rule implementation function is deprecated and will be "
+            + "removed soon. It may be temporarily re-enabled by setting "
+            + "--incompatible_disallow_struct_provider_syntax=false");
+  }
+
   /**
    * Skylark integration test that forces inlining.
    */