Revert back to the old behavior of not creating a proto source root f…

…or generated .proto files.

It was meant to be a compatible change, but alas, people seemed to depend on
the exact layout of the output tree. Will flip in 1.0 . Tracking bug:

bazelbuild#9215

RELNOTES: None.
PiperOrigin-RevId: 264581654

src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java

@@ -41,11 +41,17 @@ public class ProtoConfiguration extends Fragment implements ProtoConfigurationAp
   /** Command line options. */
   public static class Options extends FragmentOptions {
     @Option(
-        name = "experimental_generated_protos_in_virtual_imports",
-        defaultValue = "true",
+        name = "incompatible_generated_protos_in_virtual_imports",
+        defaultValue = "false",
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
-        help = "If set, generated .proto files are put into a virtual import directory.")
+        metadataTags = {
+          OptionMetadataTag.INCOMPATIBLE_CHANGE,
+          OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES
+        },
+        help =
+            "If set, generated .proto files are put into a virtual import directory. For more "
+                + "information, see https://github.com/bazelbuild/bazel/issues/9215")
     public boolean generatedProtosInVirtualImports;
 
     @Option(

src/test/java/com/google/devtools/build/lib/rules/proto/BazelProtoLibraryTest.java

@@ -370,16 +370,13 @@ public void testExternalRepoWithGeneratedProto() throws Exception {
         TestConstants.LOAD_PROTO_LIBRARY,
         "proto_library(name='a', srcs=['a.proto'], deps=['@foo//x:x'])");
 
-    String genfiles = getTargetConfiguration().getGenfilesFragment().toString();
     ConfiguredTarget a = getConfiguredTarget("//a:a");
     ProtoInfo aInfo = a.get(ProtoInfo.PROVIDER);
-    assertThat(aInfo.getTransitiveProtoSourceRoots())
-        .containsExactly(".", genfiles + "/external/foo/x/_virtual_imports/x");
+    assertThat(aInfo.getTransitiveProtoSourceRoots()).containsExactly(".", "external/foo");
 
     ConfiguredTarget x = getConfiguredTarget("@foo//x:x");
     ProtoInfo xInfo = x.get(ProtoInfo.PROVIDER);
-    assertThat(xInfo.getTransitiveProtoSourceRoots())
-        .containsExactly(genfiles + "/external/foo/x/_virtual_imports/x");
+    assertThat(xInfo.getTransitiveProtoSourceRoots()).containsExactly("external/foo");
   }
 
   @Test