Add helper to centrally define the CC toolchain type requirement.

Everything that gets a CC toolchain via CppHelper.getToolchain should use this helper.

Part of #14727.

PiperOrigin-RevId: 449233884

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

@@ -36,6 +36,7 @@
 import com.google.devtools.build.lib.analysis.RuleDefinition;
 import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
 import com.google.devtools.build.lib.analysis.config.ExecutionTransitionFactory;
+import com.google.devtools.build.lib.analysis.config.ToolchainTypeRequirement;
 import com.google.devtools.build.lib.analysis.test.InstrumentedFilesCollector.InstrumentationSpec;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.packages.Attribute.LabelLateBoundDefault;
@@ -76,6 +77,16 @@ public static Label ccToolchainTypeAttribute(RuleDefinitionEnvironment env) {
     return env.getToolsLabel(CppHelper.TOOLCHAIN_TYPE_LABEL);
   }
 
+  public static ToolchainTypeRequirement ccToolchainTypeRequirement(Label ccToolchainType) {
+    // TODO(https://github.com/bazelbuild/bazel/issues/14727): Evaluate whether this can be
+    // optional.
+    return ToolchainTypeRequirement.builder(ccToolchainType).mandatory(true).build();
+  }
+
+  public static ToolchainTypeRequirement ccToolchainTypeRequirement(RuleDefinitionEnvironment env) {
+    return ccToolchainTypeRequirement(CppRuleClasses.ccToolchainTypeAttribute(env));
+  }
+
   // Artifacts of these types are discarded from the 'hdrs' attribute in cc rules
   static final FileTypeSet DISALLOWED_HDRS_FILES =
       FileTypeSet.of(