Create flag to turn down named-ness of certain Starlark params

This change creates --experimental_restrict_named_params to make all builtin Starlark parameters which are named via legacyNamed = true to instead be treated as positional-only.

This is a step on the path to cleaning up namedness of builtin Starlark parameters.

When we finalize the list of parameters which should truly be positional-only, we can change this flag to be prefixed with --incompatible instead of --experimental, as per the incompatible change policies.

Progress toward #5010.

RELNOTES: None.
PiperOrigin-RevId: 236898018

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

diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 9ac3941..563c864 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -130,6 +130,7 @@
             + ","
             + rand.nextDouble(),
         "--experimental_platforms_api=" + rand.nextBoolean(),
+        "--experimental_restrict_named_params=" + rand.nextBoolean(),
         "--experimental_starlark_config_transitions=" + rand.nextBoolean(),
         "--experimental_transition_whitelist_location=" + rand.nextDouble(),
         "--incompatible_bzl_disallow_load_after_statement=" + rand.nextBoolean(),
@@ -177,6 +178,7 @@
         .experimentalJavaCommonCreateProviderEnabledPackages(
             ImmutableList.of(String.valueOf(rand.nextDouble()), String.valueOf(rand.nextDouble())))
         .experimentalPlatformsApi(rand.nextBoolean())
+        .experimentalRestrictNamedParams(rand.nextBoolean())
         .experimentalStarlarkConfigTransitions(rand.nextBoolean())
         .experimentalTransitionWhitelistLocation(String.valueOf(rand.nextDouble()))
         .incompatibleBzlDisallowLoadAfterStatement(rand.nextBoolean())

src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java b/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
index a7a74fc..af019ff 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/MethodLibraryTest.java
@@ -745,4 +745,13 @@
         .testIfErrorContains("None", "fail(msg=None)")
         .testEval("type(None)", "'NoneType'");
   }
+
+  @Test
+  public void testExperimentalStarlarkConfig() throws Exception {
+    new SkylarkTest("--experimental_restrict_named_params")
+        .testIfErrorContains(
+            "parameter 'elements' may not be specified by name, "
+                + "for call to method join(elements) of 'string'",
+            "','.join(elements=['foo', 'bar'])");
+  }
 }