[5.1] Fix ctx.fragments.apple.single_arch_cpu returning incorrect cpu for tools when host cpu and exec cpu are different

src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java

@@ -73,6 +73,9 @@ public class AppleConfiguration extends Fragment implements AppleConfigurationAp
   /** Prefix for iOS cpu values */
   public static final String IOS_CPU_PREFIX = "ios_";
 
+  /** Prefix for macOS cpu values */
+  private static final String MACOS_CPU_PREFIX = "darwin_";
+
   // TODO(b/180572694): Remove after platforms based toolchain resolution supported.
   /** Prefix for forced iOS simulator cpu values */
   public static final String IOS_FORCED_SIMULATOR_CPU_PREFIX = "sim_";
@@ -122,7 +125,7 @@ public static AppleCpus create(AppleCommandLineOptions options, CoreOptions core
               : ImmutableList.copyOf(options.tvosCpus);
       ImmutableList<String> macosCpus =
           (options.macosCpus == null || options.macosCpus.isEmpty())
-              ? ImmutableList.of(AppleCommandLineOptions.DEFAULT_MACOS_CPU)
+              ? ImmutableList.of(macosCpuFromCpu(coreOptions.cpu))
               : ImmutableList.copyOf(options.macosCpus);
       ImmutableList<String> catalystCpus =
           (options.catalystCpus == null || options.catalystCpus.isEmpty())
@@ -148,7 +151,7 @@ public static AppleCpus create(AppleCommandLineOptions options, CoreOptions core
     abstract ImmutableList<String> catalystCpus();
   }
 
-  /** Determines cpu value from apple-specific toolchain identifier. */
+  /** Determines iOS cpu value from apple-specific toolchain identifier. */
   public static String iosCpuFromCpu(String cpu) {
     if (cpu.startsWith(IOS_CPU_PREFIX)) {
       return cpu.substring(IOS_CPU_PREFIX.length());
@@ -157,6 +160,14 @@ public static String iosCpuFromCpu(String cpu) {
     }
   }
 
+  /** Determines macOS cpu value from apple-specific toolchain identifier. */
+  private static String macosCpuFromCpu(String cpu) {
+    if (cpu.startsWith(MACOS_CPU_PREFIX)) {
+      return cpu.substring(MACOS_CPU_PREFIX.length());
+    }
+    return AppleCommandLineOptions.DEFAULT_MACOS_CPU;
+  }
+
   public AppleCommandLineOptions getOptions() {
     return options;
   }

src/test/java/com/google/devtools/build/lib/rules/apple/AppleFragmentTest.java

@@ -0,0 +1,101 @@
+// Copyright 2022 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.rules.apple;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableMap;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.packages.Provider;
+import com.google.devtools.build.lib.packages.StarlarkProvider;
+import com.google.devtools.build.lib.packages.StructImpl;
+import com.google.devtools.build.lib.testutil.TestConstants;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests for the Starlark interface of Apple fragment. */
+@RunWith(JUnit4.class)
+public class AppleFragmentTest extends BuildViewTestCase {
+
+  @Before
+  public void setup() throws Exception {
+    scratch.file(
+        "rules.bzl",
+        "MyInfo = provider()",
+        "def _my_binary_impl(ctx):",
+        "    out = ctx.actions.declare_file(ctx.label.name)",
+        "    ctx.actions.write(out, '')",
+        "    return [",
+        "        DefaultInfo(executable = out),",
+        "        MyInfo(",
+        "            exec_cpu = ctx.fragments.apple.single_arch_cpu,",
+        "        ),",
+        "    ]",
+        "my_binary = rule(",
+        "    fragments = ['apple'],",
+        "    implementation = _my_binary_impl,",
+        ")",
+        "def _my_rule_impl(ctx):",
+        "    return ctx.attr._tool[MyInfo]",
+        "my_rule = rule(",
+        "    _my_rule_impl,",
+        "    attrs = {",
+        "        '_tool': attr.label(",
+        "            cfg = 'exec',",
+        "            executable = True,",
+        "            default = ('//:bin'),",
+        "        ),",
+        "    },",
+        ")");
+    scratch.file(
+        "BUILD",
+        "load(':rules.bzl', 'my_binary', 'my_rule')",
+        "my_binary(name = 'bin')",
+        "my_rule(name = 'a')",
+        "platform(",
+        "    name = 'macos_arm64',",
+        "    constraint_values = [",
+        "        '" + TestConstants.CONSTRAINTS_PACKAGE_ROOT + "cpu:aarch64',",
+        "        '" + TestConstants.CONSTRAINTS_PACKAGE_ROOT + "os:osx',",
+        "    ],",
+        ")");
+    scratch.file(
+        "/workspace/platform_mappings",
+        "platforms:",
+        "  //:macos_arm64",
+        "    --cpu=darwin_arm64",
+        "flags:",
+        "  --cpu=darwin_arm64",
+        "  --apple_platform_type=macos",
+        "    //:macos_arm64");
+    invalidatePackages(false);
+  }
+
+  @Test
+  public void appleFragmentSingleArchCpuOnExtraExecPlatform() throws Exception {
+    // Test that ctx.fragments.apple.single_arch_cpu returns the execution
+    // platform's cpu in a tool's rule context.
+    useConfiguration("--extra_execution_platforms=//:macos_arm64");
+    ConfiguredTarget configuredTarget = getConfiguredTarget("//:a");
+    Provider.Key key =
+        new StarlarkProvider.Key(Label.parseAbsolute("//:rules.bzl", ImmutableMap.of()), "MyInfo");
+    StructImpl myInfo = (StructImpl) configuredTarget.get(key);
+    assertThat((String) myInfo.getValue("exec_cpu")).isEqualTo("arm64");
+  }
+}

src/test/java/com/google/devtools/build/lib/rules/apple/BUILD

@@ -32,6 +32,7 @@ java_library(
         "//src/test/java/com/google/devtools/build/lib/analysis/util",
         "//src/test/java/com/google/devtools/build/lib/packages:testutil",
         "//src/test/java/com/google/devtools/build/lib/testutil",
+        "//src/test/java/com/google/devtools/build/lib/testutil:TestConstants",
         "//third_party:guava",
         "//third_party:guava-testlib",
         "//third_party:jsr305",