[clang] [clang] Absoultify paths in dependency file output (PR #117458)

[Fangrui Song via cfe-commits]

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@@ -312,11 +314,18 @@ void DependencyFileGenerator::finishedMainFile(DiagnosticsEngine &Diags) {
 /// https://msdn.microsoft.com/en-us/library/dd9y37ha.aspx for NMake info,
 /// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
 /// for Windows file-naming info.
-static void PrintFilename(raw_ostream &OS, StringRef Filename,
+static void PrintFilename(raw_ostream &OS, llvm::vfs::FileSystem *FS,
+                          StringRef Filename,
                           DependencyOutputFormat OutputFormat) {
   // Convert filename to platform native path
   llvm::SmallString<256> NativePath;
   llvm::sys::path::native(Filename.str(), NativePath);
+  // Make path absolute. Make and Ninja canonicalize paths without checking for
+  // symbolic links in the path, for performance concerns.
+  // If there is something like `/bin/../lib64` -> `/usr/lib64`
+  // (where `/bin` links to `/usr/bin`), Make will see them as `/lib64`.
+  if (FS != nullptr && llvm::sys::path::is_absolute(NativePath))
+    FS->makeAbsolute(NativePath);
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MaskRay wrote:

`makeAbsolute` does not resolve an absolute path, so this does not work as intended.

`Make path absolute` => `Resolve an absolute path`?

https://github.com/llvm/llvm-project/pull/117458