[clang-scan-deps] [P1689] Keep consistent behavior for make dependencies with clang (#69551)

Close #69439.

This patch tries to reuse the codes to generate make style dependencies
information with P1689 format directly.

Author: ChuanqiXu9

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -666,12 +666,24 @@ static StringRef makeAbsoluteAndPreferred(CompilerInstance &CI, StringRef Path,
 }
 
 void ModuleDepCollector::addFileDep(StringRef Path) {
+  if (IsStdModuleP1689Format) {
+    // Within P1689 format, we don't want all the paths to be absolute path
+    // since it may violate the tranditional make style dependencies info.
+    FileDeps.push_back(std::string(Path));
+    return;
+  }
+
   llvm::SmallString<256> Storage;
   Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
   FileDeps.push_back(std::string(Path));
 }
 
 void ModuleDepCollector::addFileDep(ModuleDeps &MD, StringRef Path) {
+  if (IsStdModuleP1689Format) {
+    MD.FileDeps.insert(Path);
+    return;
+  }
+
   llvm::SmallString<256> Storage;
   Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
   MD.FileDeps.insert(Path);

clang/test/ClangScanDeps/P1689.cppm

@@ -42,6 +42,14 @@
 // RUN: clang-scan-deps -format=p1689 \
 // RUN:   -- %clang++ -std=c++20 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -c %t/impl_part.cppm -o %t/impl_part.o \
 // RUN:   | FileCheck %t/impl_part.cppm -DPREFIX=%/t
+//
+// Check the path in the make style dependencies are generated in relative path form
+// RUN: cd %t
+// RUN: clang-scan-deps -format=p1689 \
+// RUN:   -- %clang++ -std=c++20 -c -fprebuilt-module-path=%t impl_part.cppm -o impl_part.o \
+// RUN:      -MT impl_part.o.ddi -MD -MF impl_part.dep
+// RUN:   cat impl_part.dep | FileCheck impl_part.cppm -DPREFIX=%/t --check-prefix=CHECK-MAKE-RELATIVE
+
 
 //--- P1689.json.in
 [
@@ -168,6 +176,8 @@ void World() {
 // CHECK-MAKE:   [[PREFIX]]/impl_part.cppm
 // CHECK-MAKE:   [[PREFIX]]/header.mock
 
+// CHECK-MAKE-RELATIVE: impl_part.o.ddi: impl_part.cppm header.mock
+
 //--- interface_part.cppm
 export module M:interface_part;
 export void World();