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

[Ben Langmuir via cfe-commits]

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@@ -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));
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benlangmuir wrote:

This is a use-after-free of `Storage` since `Path` will point to that buffer if the string is modified. Same for the other case below.

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