Reset platform on cpu transitions.

With platform mappings about to be enabled we need to make sure that platforms are reset in any configuration transitions that write flags which may impact the platform. Otherwise a platform may be set before the transition that matches the old flags but platform mapping would not be triggered for the new flag values (because platform mapping only happens if no platform is set).

Step 6/N towards the platforms mapping functionality for #6426

RELNOTES: None.
PiperOrigin-RevId: 244696779

src/main/java/com/google/devtools/build/lib/rules/android/AndroidRuleClasses.java

@@ -30,6 +30,7 @@
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.analysis.BaseRuleClasses;
+import com.google.devtools.build.lib.analysis.PlatformOptions;
 import com.google.devtools.build.lib.analysis.RuleDefinition;
 import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
@@ -212,22 +213,19 @@ public static LabelLateBoundDefault<?> getAndroidSdkLabel(Label androidSdk) {
   /** Android Split configuration transition for properly handling native dependencies */
   public static final class AndroidSplitTransition
       implements SplitTransition, AndroidSplitTransititionApi {
-    private static void setCrosstoolToAndroid(BuildOptions output, BuildOptions input) {
-      AndroidConfiguration.Options inputAndroidOptions =
-          input.get(AndroidConfiguration.Options.class);
-      AndroidConfiguration.Options outputAndroidOptions =
-          output.get(AndroidConfiguration.Options.class);
-
-      CppOptions cppOptions = output.get(CppOptions.class);
-      if (inputAndroidOptions.androidCrosstoolTop != null
-          && !cppOptions.crosstoolTop.equals(inputAndroidOptions.androidCrosstoolTop)) {
+    private static void setCrosstoolToAndroid(BuildOptions options) {
+      AndroidConfiguration.Options androidOptions = options.get(AndroidConfiguration.Options.class);
+
+      CppOptions cppOptions = options.get(CppOptions.class);
+      if (androidOptions.androidCrosstoolTop != null
+          && !cppOptions.crosstoolTop.equals(androidOptions.androidCrosstoolTop)) {
         if (cppOptions.hostCrosstoolTop == null) {
           cppOptions.hostCrosstoolTop = cppOptions.crosstoolTop;
         }
-        cppOptions.crosstoolTop = inputAndroidOptions.androidCrosstoolTop;
+        cppOptions.crosstoolTop = androidOptions.androidCrosstoolTop;
       }
 
-      outputAndroidOptions.configurationDistinguisher = ConfigurationDistinguisher.ANDROID;
+      androidOptions.configurationDistinguisher = ConfigurationDistinguisher.ANDROID;
     }
 
     @Override
@@ -248,11 +246,8 @@ public List<BuildOptions> split(BuildOptions buildOptions) {
         } else {
 
           BuildOptions splitOptions = buildOptions.clone();
-          splitOptions.get(CppOptions.class).cppCompiler = androidOptions.cppCompiler;
-          splitOptions.get(CppOptions.class).libcTopLabel = androidOptions.androidLibcTopLabel;
           splitOptions.get(BuildConfiguration.Options.class).cpu = androidOptions.cpu;
-          splitOptions.get(CppOptions.class).dynamicMode = androidOptions.dynamicMode;
-          setCrosstoolToAndroid(splitOptions, buildOptions);
+          setCommonAndroidOptions(androidOptions, splitOptions);
           return ImmutableList.of(splitOptions);
         }
 
@@ -268,16 +263,24 @@ public List<BuildOptions> split(BuildOptions buildOptions) {
           // TODO(bazel-team): --android_cpu doesn't follow --cpu right now; it should.
           splitOptions.get(AndroidConfiguration.Options.class).cpu = cpu;
           splitOptions.get(BuildConfiguration.Options.class).cpu = cpu;
-          splitOptions.get(CppOptions.class).cppCompiler = androidOptions.cppCompiler;
-          splitOptions.get(CppOptions.class).libcTopLabel = androidOptions.androidLibcTopLabel;
-          splitOptions.get(CppOptions.class).dynamicMode = androidOptions.dynamicMode;
-          setCrosstoolToAndroid(splitOptions, buildOptions);
+          setCommonAndroidOptions(androidOptions, splitOptions);
           result.add(splitOptions);
         }
         return result.build();
       }
     }
 
+    private void setCommonAndroidOptions(
+        AndroidConfiguration.Options androidOptions, BuildOptions newOptions) {
+      newOptions.get(CppOptions.class).cppCompiler = androidOptions.cppCompiler;
+      newOptions.get(CppOptions.class).libcTopLabel = androidOptions.androidLibcTopLabel;
+      newOptions.get(CppOptions.class).dynamicMode = androidOptions.dynamicMode;
+      setCrosstoolToAndroid(newOptions);
+
+      // Ensure platforms aren't set so that platform mapping can take place.
+      newOptions.get(PlatformOptions.class).platforms = ImmutableList.of();
+    }
+
     @Override
     public boolean isImmutable() {
       return true;

src/main/java/com/google/devtools/build/lib/rules/objc/AppleCrosstoolTransition.java

@@ -16,6 +16,7 @@
 
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.analysis.PlatformOptions;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.config.BuildOptions;
 import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition;
@@ -96,6 +97,9 @@ public static void setAppleCrosstoolTransitionConfiguration(BuildOptions from,
 
     // OSX toolchains do not support fission.
     to.get(CppOptions.class).fissionModes = ImmutableList.of();
+
+    // Ensure platforms aren't set so that platform mapping can take place.
+    to.get(PlatformOptions.class).platforms = ImmutableList.of();
   }
 
   /**