[clang] [clang modules] Setting `DebugCompilationDir` when it is safe to ignore current working directory (PR #128446)

[Qiongsi Wu via cfe-commits]

https://github.com/qiongsiwu updated https://github.com/llvm/llvm-project/pull/128446

>From c8eda8b9192cf4bdad4121063336beeb14cbe689 Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu at apple.com>
Date: Sun, 23 Feb 2025 16:47:18 -0800
Subject: [PATCH 1/3] Initial commit

---
 .../DependencyScanning/ModuleDepCollector.cpp | 17 +++++++++++++-
 clang/test/ClangScanDeps/modules-debug-dir.c  | 22 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/ClangScanDeps/modules-debug-dir.c

diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index 1c5f4c4b50ab6..8a94535d3806c 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -492,8 +492,23 @@ static std::string getModuleContextHash(const ModuleDeps &MD,
   auto &FSOpts = const_cast<FileSystemOptions &>(CI.getFileSystemOpts());
   if (CWD && !IgnoreCWD)
     HashBuilder.add(*CWD);
-  else
+  else {
     FSOpts.WorkingDir.clear();
+    auto &CGOpts = const_cast<CodeGenOptions &>(CI.getCodeGenOpts());
+    if (CGOpts.DwarfVersion && CWD) {
+      // It is necessary to explicitly set the DebugCompilationDir
+      // to a common directory (e.g. root) if IgnoreCWD is true.
+      // When IgnoreCWD is true, the module's content should not depend
+      // on the current working directory. However, if dwarf information
+      // is needed (when CGOpts.DwarfVersion is non-zero), and if
+      // CGOpts.DebugCompilationDir is not explicitly set,
+      // the current working directory will be automatically embedded
+      // in the dwarf information in the pcm, contradicting the assumption
+      // that it is safe to ignore the CWD. Thus in such cases,
+      // CGOpts.DebugCompilationDir is explicitly set to a common directory.
+      CGOpts.DebugCompilationDir = llvm::sys::path::root_path(*CWD);
+    }
+  }
 
   // Hash the BuildInvocation without any input files.
   SmallString<0> ArgVec;
diff --git a/clang/test/ClangScanDeps/modules-debug-dir.c b/clang/test/ClangScanDeps/modules-debug-dir.c
new file mode 100644
index 0000000000000..580f72205e68f
--- /dev/null
+++ b/clang/test/ClangScanDeps/modules-debug-dir.c
@@ -0,0 +1,22 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.in > %t/cdb.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -format \
+// RUN:   experimental-full > %t/result.json
+
+//--- cdb.json.in
+[{
+  "directory": "DIR",
+  "command": "clang -g -fdebug-info-for-profiling DIR/tu.c -fmodules -fmodules-cache-path=DIR/cache -IDIR/include/ -o DIR/tu.o",
+  "file": "DIR/tu.c"
+}]
+
+//--- include/module.modulemap
+module mod {
+  header "mod.h"
+}
+
+//--- include/mod.h
+
+//--- tu.c
+#include "mod.h"

>From 4b29c19ebc360ec80a8c16e1ac485bbac78a9062 Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu at apple.com>
Date: Mon, 24 Feb 2025 09:34:56 -0800
Subject: [PATCH 2/3] Fix the test.

---
 clang/test/ClangScanDeps/modules-debug-dir.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/clang/test/ClangScanDeps/modules-debug-dir.c b/clang/test/ClangScanDeps/modules-debug-dir.c
index 580f72205e68f..1ac518985471d 100644
--- a/clang/test/ClangScanDeps/modules-debug-dir.c
+++ b/clang/test/ClangScanDeps/modules-debug-dir.c
@@ -3,11 +3,12 @@
 // RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.in > %t/cdb.json
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format \
 // RUN:   experimental-full > %t/result.json
+// RUN: cat %t/result.json | FileCheck %s
 
 //--- cdb.json.in
 [{
   "directory": "DIR",
-  "command": "clang -g -fdebug-info-for-profiling DIR/tu.c -fmodules -fmodules-cache-path=DIR/cache -IDIR/include/ -o DIR/tu.o",
+  "command": "clang -c -g -gmodules DIR/tu.c -fmodules -fmodules-cache-path=DIR/cache -IDIR/include/ -fdebug-compilation-dir=DIR -o DIR/tu.o",
   "file": "DIR/tu.c"
 }]
 
@@ -20,3 +21,10 @@ module mod {
 
 //--- tu.c
 #include "mod.h"
+
+// Check the -fdebug-compilation-dir used for the module is the root
+// directory when current working directory optimization is in effect.
+// CHECK:  "modules": [
+// CHECK: "command-line": [
+// CHECK: "-fdebug-compilation-dir={{\/|C:|\/\/net}}",
+// CHECK:  "translation-units": [

>From 5c53c84d33ad4ceec4e79dc36638e827607709ca Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu at apple.com>
Date: Mon, 24 Feb 2025 10:34:35 -0800
Subject: [PATCH 3/3] Try to fix the test on windows.

---
 clang/test/ClangScanDeps/modules-debug-dir.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/test/ClangScanDeps/modules-debug-dir.c b/clang/test/ClangScanDeps/modules-debug-dir.c
index 1ac518985471d..87f1bc141c73a 100644
--- a/clang/test/ClangScanDeps/modules-debug-dir.c
+++ b/clang/test/ClangScanDeps/modules-debug-dir.c
@@ -8,7 +8,7 @@
 //--- cdb.json.in
 [{
   "directory": "DIR",
-  "command": "clang -c -g -gmodules DIR/tu.c -fmodules -fmodules-cache-path=DIR/cache -IDIR/include/ -fdebug-compilation-dir=DIR -o DIR/tu.o",
+  "command": "clang -target x86_64-apple-darwin -c -g -gmodules DIR/tu.c -fmodules -fmodules-cache-path=DIR/cache -IDIR/include/ -fdebug-compilation-dir=DIR -o DIR/tu.o",
   "file": "DIR/tu.c"
 }]
 
@@ -26,5 +26,5 @@ module mod {
 // directory when current working directory optimization is in effect.
 // CHECK:  "modules": [
 // CHECK: "command-line": [
-// CHECK: "-fdebug-compilation-dir={{\/|C:|\/\/net}}",
+// CHECK: "-fdebug-compilation-dir=/",
 // CHECK:  "translation-units": [