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

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 updated https://github.com/llvm/llvm-project/pull/69551

>From c91007b51e164d22c8f73a864105494ebc10a004 Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Mon, 30 Oct 2023 11:51:04 +0800
Subject: [PATCH] [clang-scan-deps] [P1689] Keep consistent behavior for make
 dependencies with clang

Close #69439.

This patch tries to reuse the codes to generate make style dependencies
information with P1689 format directly.
---
 .../DependencyScanning/ModuleDepCollector.cpp      | 14 ++++++++++----
 clang/test/ClangScanDeps/P1689.cppm                | 10 ++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index 40115b7b5ae25b3..3764ccb0b4749b1 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -666,13 +666,19 @@ static StringRef makeAbsoluteAndPreferred(CompilerInstance &CI, StringRef Path,
 }
 
 void ModuleDepCollector::addFileDep(StringRef Path) {
-  llvm::SmallString<256> Storage;
-  Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
+  // Within P1689 format, we don't want all the paths to be absolute path
+  // since it may violate the tranditional make style dependencies info.
+  if (!IsStdModuleP1689Format) {
+    llvm::SmallString<256> Storage;
+    Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
+  }
   FileDeps.push_back(std::string(Path));
 }
 
 void ModuleDepCollector::addFileDep(ModuleDeps &MD, StringRef Path) {
-  llvm::SmallString<256> Storage;
-  Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
+  if (!IsStdModuleP1689Format) {
+    llvm::SmallString<256> Storage;
+    Path = makeAbsoluteAndPreferred(ScanInstance, Path, Storage);
+  }
   MD.FileDeps.insert(Path);
 }
diff --git a/clang/test/ClangScanDeps/P1689.cppm b/clang/test/ClangScanDeps/P1689.cppm
index dffb16974a3e4e4..24632e25cf7f3bd 100644
--- a/clang/test/ClangScanDeps/P1689.cppm
+++ b/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();