Expose the --incompatible_enable_cc_toolchain_resolution flag to Starlark and

update find_cpp_toolchain to use it.

Part of #7260.

PiperOrigin-RevId: 231400764

Author: katre

src/main/java/com/google/devtools/build/lib/rules/cpp/CcModule.java

@@ -87,7 +87,8 @@ public class CcModule
         CcCompilationContext,
         CcLinkingContext,
         LibraryToLinkWrapper,
-        CcToolchainVariables> {
+        CcToolchainVariables,
+        SkylarkRuleContext> {
 
   private enum RegisterActions {
     ALWAYS,
@@ -1508,4 +1509,9 @@ private static void getLegacyArtifactNamePatterns(
   private static <T> T nullIfNone(Object object, Class<T> type) {
     return object != Runtime.NONE ? type.cast(object) : null;
   }
+
+  @Override
+  public boolean isCcToolchainResolutionEnabled(SkylarkRuleContext skylarkRuleContext) {
+    return CppHelper.useToolchainResolution(skylarkRuleContext.getRuleContext());
+  }
 }

src/main/java/com/google/devtools/build/lib/skylarkbuildapi/cpp/BazelCcModuleApi.java

@@ -48,7 +48,8 @@ public interface BazelCcModuleApi<
         CcCompilationContextT,
         LinkingContextT,
         LibraryToLinkWrapperT,
-        CcToolchainVariablesT> {
+        CcToolchainVariablesT,
+        SkylarkRuleContextT> {
 
   @SkylarkCallable(
       name = "compile",

src/main/java/com/google/devtools/build/lib/skylarkbuildapi/cpp/CcModuleApi.java

@@ -18,6 +18,7 @@
 import com.google.devtools.build.lib.skylarkbuildapi.FileApi;
 import com.google.devtools.build.lib.skylarkbuildapi.ProviderApi;
 import com.google.devtools.build.lib.skylarkbuildapi.SkylarkActionFactoryApi;
+import com.google.devtools.build.lib.skylarkbuildapi.SkylarkRuleContextApi;
 import com.google.devtools.build.lib.skylarkinterface.Param;
 import com.google.devtools.build.lib.skylarkinterface.ParamType;
 import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
@@ -39,7 +40,8 @@ public interface CcModuleApi<
     CompilationContextT extends CcCompilationContextApi,
     LinkingContextT extends CcLinkingContextApi,
     LibraryToLinkWrapperT extends LibraryToLinkWrapperApi,
-    CcToolchainVariablesT extends CcToolchainVariablesApi> {
+    CcToolchainVariablesT extends CcToolchainVariablesApi,
+    SkylarkRuleContextT extends SkylarkRuleContextApi> {
 
   @SkylarkCallable(
       name = "CcToolchainInfo",
@@ -669,4 +671,18 @@ CompilationContextT createCcCompilationContext(
             type = CcToolchainProviderApi.class)
       })
   String legacyCcFlagsMakeVariable(CcToolchainProviderT ccToolchain);
+
+  @SkylarkCallable(
+      name = "is_cc_toolchain_resolution_enabled_do_not_use",
+      documented = false,
+      parameters = {
+        @Param(
+            name = "ctx",
+            positional = false,
+            named = true,
+            type = SkylarkRuleContextApi.class,
+            doc = "The rule context."),
+      },
+      doc = "Returns true if the --incompatible_enable_cc_toolchain_resolution flag is enabled.")
+  boolean isCcToolchainResolutionEnabled(SkylarkRuleContextT ruleContext);
 }

src/main/java/com/google/devtools/build/skydoc/fakebuildapi/cpp/FakeCcModule.java

@@ -156,6 +156,11 @@ public String legacyCcFlagsMakeVariable(CcToolchainProviderApi ccToolchain) {
     return "";
   }
 
+  @Override
+  public boolean isCcToolchainResolutionEnabled(SkylarkRuleContextApi ruleContext) {
+    return false;
+  }
+
   @Override
   public CompilationInfoApi compile(
       SkylarkRuleContextApi skylarkRuleContext,

src/test/java/com/google/devtools/build/lib/rules/cpp/SkylarkCcCommonTest.java

@@ -4636,4 +4636,41 @@ public void testGetLegacyCcFlagsMakeVariable() throws Exception {
 
     assertThat(ccFlags).isEqualTo("-test-cflag1 -testcflag2");
   }
+
+  private boolean toolchainResolutionEnabled() throws Exception {
+    scratch.file(
+        "a/rule.bzl",
+        "def _impl(ctx):",
+        "  toolchain_resolution_enabled = cc_common.is_cc_toolchain_resolution_enabled_do_not_use(",
+        "      ctx = ctx)",
+        "  return struct(",
+        "    toolchain_resolution_enabled = toolchain_resolution_enabled)",
+        "toolchain_resolution_enabled = rule(",
+        "  _impl,",
+        ");");
+
+    scratch.file(
+        "a/BUILD",
+        "load(':rule.bzl', 'toolchain_resolution_enabled')",
+        "toolchain_resolution_enabled(name='r')");
+
+    ConfiguredTarget r = getConfiguredTarget("//a:r");
+    @SuppressWarnings("unchecked") // Use an extra variable in order to suppress the warning.
+    boolean toolchainResolutionEnabled = (boolean) r.get("toolchain_resolution_enabled");
+    return toolchainResolutionEnabled;
+  }
+
+  @Test
+  public void testIsToolchainResolutionEnabled_disabled() throws Exception {
+    useConfiguration("--incompatible_enable_cc_toolchain_resolution=false");
+
+    assertThat(toolchainResolutionEnabled()).isFalse();
+  }
+
+  @Test
+  public void testIsToolchainResolutionEnabled_enabled() throws Exception {
+    useConfiguration("--incompatible_enable_cc_toolchain_resolution");
+
+    assertThat(toolchainResolutionEnabled()).isTrue();
+  }
 }

tools/cpp/toolchain_utils.bzl

@@ -33,10 +33,17 @@ def find_cpp_toolchain(ctx):
     Returns:
       A CcToolchainProvider.
     """
-    if not hasattr(ctx.attr, "_cc_toolchain"):
-        fail("In order to use find_cpp_toolchain, you must define the '_cc_toolchain' attribute on your rule or aspect.")
 
-    if Label("@bazel_tools//tools/cpp:toolchain_type") in ctx.fragments.platform.enabled_toolchain_types:
+    # Check the incompatible flag for toolchain resolution.
+    if hasattr(cc_common, "is_cc_toolchain_resolution_enabled_do_not_use") and cc_common.is_cc_toolchain_resolution_enabled_do_not_use(ctx = ctx):
         return ctx.toolchains["@bazel_tools//tools/cpp:toolchain_type"]
-    else:
+
+    if Label("//tools/cpp:toolchain_type") in ctx.fragments.platform.enabled_toolchain_types:
+        return ctx.toolchains["@bazel_tools//tools/cpp:toolchain_type"]
+
+    # Fall back to the legacy implicit attribute lookup.
+    if hasattr(ctx.attr, "_cc_toolchain"):
         return ctx.attr._cc_toolchain[cc_common.CcToolchainInfo]
+
+    # We didn't find anything.
+    fail("In order to use find_cpp_toolchain, you must include the '@bazel_tools//tools/cpp:toolchain_type' in the toolchains argument to your rule.")