Automated rollback of commit 536a166.

*** Reason for rollback ***

Found an incremental correctness concern with build settings. Rolling back while investigating and to rollback for the bazel release

*** Original change description ***

Turn on --experimental_build_setting_api

RELNOTES: Turn on --experimental_build_setting_api by default for starlark build settings (see https://docs.bazel.build/versions/master/skylark/config.html#user-defined-build-settings for more info)

SKIP_CI=blaze is borked
PiperOrigin-RevId: 252715211

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

@@ -77,7 +77,7 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
 
   @Option(
       name = "experimental_build_setting_api",
-      defaultValue = "true",
+      defaultValue = "false",
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = OptionEffectTag.BUILD_FILE_SEMANTICS,
       help =

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

@@ -218,7 +218,7 @@ public static Builder builderWithDefaults() {
   public static final StarlarkSemantics DEFAULT_SEMANTICS =
       builder()
           // <== Add new options here in alphabetic order ==>
-          .experimentalBuildSettingApi(true)
+          .experimentalBuildSettingApi(false)
           .experimentalCcSkylarkApiEnabledPackages(ImmutableList.of())
           .experimentalAllowIncrementalRepositoryUpdates(false)
           .experimentalEnableAndroidMigrationApis(false)

src/test/shell/integration/starlark_configurations_test.sh

@@ -161,6 +161,19 @@ function test_dont_parse_flags_after_dash_dash() {
   expect_log "invalid package name '-//test_dont_parse_flags_after_dash_dash'"
 }
 
+function test_doesnt_work_without_experimental_flag() {
+  local -r pkg=$FUNCNAME
+  mkdir -p $pkg
+
+  write_build_setting_bzl
+
+  bazel build //$pkg:my_drink --//$pkg:type=coffee > output 2>"$TEST_log" \
+    && fail "Expected failure"
+
+  expect_log "Error loading option //$pkg:type:"
+  expect_log "Extension file '$pkg/build_setting.bzl' has errors"
+}
+
 function test_multiple_starlark_flags() {
   local -r pkg=$FUNCNAME
   mkdir -p $pkg