[clang] Make explicitly-built modules independent of the CWD (#164840)

PR https://github.com/llvm/llvm-project/pull/150123 changed how we
normalize the modules cache path. Unfortunately, empty path would get
normalized to the current working directory. This means that even
explicitly-built PCMs that don't rely on the CWD now embed it, leading
to surprising behavior. This PR fixes that by normalizing an empty
modules cache path to an empty string.

1 files changed, 1 insertions, 4 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 374138fe4cf8..e3bf0eaa3c39 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -546,14 +546,11 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
 std::string CompilerInstance::getSpecificModuleCachePath(StringRef ModuleHash) {
   assert(FileMgr && "Specific module cache path requires a FileManager");
 
-  if (getHeaderSearchOpts().ModuleCachePath.empty())
-    return "";
-
   // Set up the module path, including the hash for the module-creation options.
   SmallString<256> SpecificModuleCache;
   normalizeModuleCachePath(*FileMgr, getHeaderSearchOpts().ModuleCachePath,
                            SpecificModuleCache);
-  if (!getHeaderSearchOpts().DisableModuleHash)
+  if (!SpecificModuleCache.empty() && !getHeaderSearchOpts().DisableModuleHash)
     llvm::sys::path::append(SpecificModuleCache, ModuleHash);
   return std::string(SpecificModuleCache);
 }