Make skipping the parse_headers action also conditional on a crosstool feature.

Not all crosstools might sufficiently validate layering_check otherwise,
e.g. Clang needs a version that includes https://reviews.llvm.org/D132779.

PiperOrigin-RevId: 483907290
Change-Id: I5a9994258f2345ea390b028fb15859c6c9484794

Author: djasper-gh

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

@@ -1566,6 +1566,7 @@ private CcCompilationOutputs createCcCompileActions() throws RuleErrorException
         continue;
       }
       if (cppConfiguration.getParseHeadersSkippedIfCorrespondingSrcsFound()
+          && featureConfiguration.isEnabled(CppRuleClasses.VALIDATES_LAYERING_CHECK_IN_TEXTUAL_HDRS)
           && compiledBasenames.contains(
               Files.getNameWithoutExtension(artifact.getExecPathString()))) {
         continue;

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

@@ -168,6 +168,15 @@ public static ToolchainTypeRequirement ccToolchainTypeRequirement(RuleDefinition
   /** A string constant for the layering_check feature. */
   public static final String LAYERING_CHECK = "layering_check";
 
+  /**
+   * A string constant that signifies whether the crosstool validates layering_check in
+   * textual_hdrs. We use the compiler's definition of textual_hdrs also for all regular but
+   * non-modular headers. This in turn means that the compiler can check layering in headers of the
+   * same target, irrespective the PARSE_HEADERS feature and we can elide separate header actions.
+   */
+  public static final String VALIDATES_LAYERING_CHECK_IN_TEXTUAL_HDRS =
+      "validates_layering_check_in_textual_hdrs";
+
   /** A string constant for the header_modules feature. */
   public static final String HEADER_MODULES = "header_modules";