[clang] 1ab6c0d - [clang] Make explicitly-built modules independent of the CWD (#164840)

[via cfe-commits]

Author: Jan Svoboda
Date: 2025-10-23T10:09:50-07:00
New Revision: 1ab6c0d60c52539b77e1cbfdc7f1ba47ad140b8d

URL: https://github.com/llvm/llvm-project/commit/1ab6c0d60c52539b77e1cbfdc7f1ba47ad140b8d
DIFF: https://github.com/llvm/llvm-project/commit/1ab6c0d60c52539b77e1cbfdc7f1ba47ad140b8d.diff

LOG: [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.

Added: 
    clang/test/Modules/explicit-build-cwd.c

Modified: 
    clang/lib/Frontend/CompilerInstance.cpp
    clang/lib/Lex/HeaderSearch.cpp
    clang/lib/Tooling/DependencyScanning/DependencyScannerImpl.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 374138fe4cf8f..e3bf0eaa3c391 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);
 }

diff  --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 238c5e2f2d9a5..65c324c10ca5d 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -2186,6 +2186,8 @@ std::string HeaderSearch::suggestPathToFileForDiagnostics(
 void clang::normalizeModuleCachePath(FileManager &FileMgr, StringRef Path,
                                      SmallVectorImpl<char> &NormalizedPath) {
   NormalizedPath.assign(Path.begin(), Path.end());
-  FileMgr.makeAbsolutePath(NormalizedPath);
-  llvm::sys::path::remove_dots(NormalizedPath);
+  if (!NormalizedPath.empty()) {
+    FileMgr.makeAbsolutePath(NormalizedPath);
+    llvm::sys::path::remove_dots(NormalizedPath);
+  }
 }

diff  --git a/clang/lib/Tooling/DependencyScanning/DependencyScannerImpl.cpp b/clang/lib/Tooling/DependencyScanning/DependencyScannerImpl.cpp
index 05d566922a441..42f52d0ff6241 100644
--- a/clang/lib/Tooling/DependencyScanning/DependencyScannerImpl.cpp
+++ b/clang/lib/Tooling/DependencyScanning/DependencyScannerImpl.cpp
@@ -524,13 +524,12 @@ bool initializeScanCompilerInstance(
   // Use the dependency scanning optimized file system if requested to do so.
   if (DepFS) {
     DepFS->resetBypassedPathPrefix();
-    if (!ScanInstance.getHeaderSearchOpts().ModuleCachePath.empty()) {
-      SmallString<256> ModulesCachePath;
-      normalizeModuleCachePath(
-          ScanInstance.getFileManager(),
-          ScanInstance.getHeaderSearchOpts().ModuleCachePath, ModulesCachePath);
+    SmallString<256> ModulesCachePath;
+    normalizeModuleCachePath(ScanInstance.getFileManager(),
+                             ScanInstance.getHeaderSearchOpts().ModuleCachePath,
+                             ModulesCachePath);
+    if (!ModulesCachePath.empty())
       DepFS->setBypassedPathPrefix(ModulesCachePath);
-    }
 
     ScanInstance.setDependencyDirectivesGetter(
         std::make_unique<ScanningDependencyDirectivesGetter>(

diff  --git a/clang/test/Modules/explicit-build-cwd.c b/clang/test/Modules/explicit-build-cwd.c
new file mode 100644
index 0000000000000..af8b74361d685
--- /dev/null
+++ b/clang/test/Modules/explicit-build-cwd.c
@@ -0,0 +1,17 @@
+// This test checks that explicitly building the same module from 
diff erent
+// working directories results in the same PCM contents.
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: mkdir %t/one
+// RUN: mkdir %t/two
+
+//--- module.modulemap
+module M { header "M.h" }
+
+//--- M.h
+
+// RUN: cd %t/one && %clang_cc1 -fmodules -emit-module %t/module.modulemap -fmodule-name=M -o %t/M_one.pcm
+// RUN: cd %t/two && %clang_cc1 -fmodules -emit-module %t/module.modulemap -fmodule-name=M -o %t/M_two.pcm
+
+// RUN: 
diff  %t/M_one.pcm %t/M_two.pcm