Add a flag that alters the behavior of the parse_headers feature. With the

flag, the headers of a target are compiled into a C++ module instead of being
parsed as their own translation unit. The module otherwise remains unused.

This way, parse_headers can be used to get a codebase ready for C++ modules.
parse_headers currently already gets close, but there are still ways in which a
header can be modules-incompatible although it parses fine.

--
PiperOrigin-RevId: 145729231
MOS_MIGRATED_REVID=145729231

1 files changed, 4 insertions, 2 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileActionBuilder.java
index 60ed762d1b..5d513a516d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileActionBuilder.java
@@ -212,9 +212,11 @@ public class CppCompileActionBuilder {
       return CppCompileAction.CPP_MODULE_COMPILE;
     } else if (CppFileTypes.CPP_HEADER.matches(sourcePath)) {
       // TODO(bazel-team): Handle C headers that probably don't work in C++ mode.
-      if (featureConfiguration.isEnabled(CppRuleClasses.PARSE_HEADERS)) {
+      if (!cppConfiguration.getParseHeadersVerifiesModules()
+          && featureConfiguration.isEnabled(CppRuleClasses.PARSE_HEADERS)) {
         return CppCompileAction.CPP_HEADER_PARSING;
-      } else if (featureConfiguration.isEnabled(CppRuleClasses.PREPROCESS_HEADERS)) {
+      } else if (!cppConfiguration.getParseHeadersVerifiesModules()
+          && featureConfiguration.isEnabled(CppRuleClasses.PREPROCESS_HEADERS)) {
         return CppCompileAction.CPP_HEADER_PREPROCESSING;
       } else {
         // CcCommon.collectCAndCppSources() ensures we do not add headers to