[clang] Canonicalize absolute paths in dependency file (#117458)

This fixes #117438.

If paths in dependency file are not absoulte, make (or ninja) will
canonicalize them.
While their canonicalization does not involves symbolic links expansion
(for IO performance concerns), leaving a non-absolute path in dependency
file may lead to unexpected canonicalization.
For example, '/a/../b', where '/a' is a symlink to '/c/d', it should be
'/c/b' but make (and ninja) canonicalizes it as '/b', and fails for file
not found.

Author: xtexx

clang/include/clang/Frontend/Utils.h

@@ -120,6 +120,7 @@ class DependencyFileGenerator : public DependencyCollector {
 private:
   void outputDependencyFile(DiagnosticsEngine &Diags);
 
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS;
   std::string OutputFile;
   std::vector<std::string> Targets;
   bool IncludeSystemHeaders;

clang/lib/Frontend/DependencyFile.cpp

@@ -10,11 +10,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Frontend/Utils.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Frontend/DependencyOutputOptions.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Frontend/Utils.h"
 #include "clang/Lex/DirectoryLookup.h"
 #include "clang/Lex/ModuleMap.h"
 #include "clang/Lex/PPCallbacks.h"
@@ -23,8 +23,10 @@
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include <optional>
+#include <system_error>
 
 using namespace clang;
 
@@ -236,6 +238,7 @@ void DependencyFileGenerator::attachToPreprocessor(Preprocessor &PP) {
     PP.SetSuppressIncludeNotFoundError(true);
 
   DependencyCollector::attachToPreprocessor(PP);
+  FS = PP.getFileManager().getVirtualFileSystemPtr();
 }
 
 bool DependencyFileGenerator::sawDependency(StringRef Filename, bool FromModule,
@@ -312,11 +315,22 @@ 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);
+  // Resolve absolute path. 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)) {
+    llvm::SmallString<256> NativePathTmp = NativePath;
+    std::error_code EC = FS->getRealPath(NativePathTmp, NativePath);
+    if (EC)
+      NativePath = NativePathTmp;
+  }
 
   if (OutputFormat == DependencyOutputFormat::NMake) {
     // Add quotes if needed. These are the characters listed as "special" to
@@ -400,7 +414,7 @@ void DependencyFileGenerator::outputDependencyFile(llvm::raw_ostream &OS) {
       Columns = 2;
     }
     OS << ' ';
-    PrintFilename(OS, File, OutputFormat);
+    printFilename(OS, FS.get(), File, OutputFormat);
     Columns += N + 1;
   }
   OS << '\n';
@@ -411,7 +425,7 @@ void DependencyFileGenerator::outputDependencyFile(llvm::raw_ostream &OS) {
     for (auto I = Files.begin(), E = Files.end(); I != E; ++I) {
       if (Index++ == InputFileIndex)
         continue;
-      PrintFilename(OS, *I, OutputFormat);
+      printFilename(OS, FS.get(), *I, OutputFormat);
       OS << ":\n";
     }
   }

clang/test/Frontend/dependency-gen-symlink.c

@@ -15,7 +15,7 @@
 // CHECK: dependency-gen-symlink.c.o
 // CHECK: dependency-gen-symlink.c
 // CHECK: a/header.h
-// CHECK: b/header.h
+// CHECK-NOT: b/header.h
 // CHECK-NOT: with-header-guard.h
 #include "a/header.h"
 #include "b/header.h"

clang/test/Frontend/dependency-gen-windows-duplicates.c

@@ -9,7 +9,7 @@
 // RUN: %clang -MD -MF - %t.dir/test.c -fsyntax-only -I %t.dir/subdir | FileCheck %s
 // CHECK: test.o:
 // CHECK-NEXT: \test.c
-// CHECK-NEXT: \SubDir\X.h
+// CHECK-NEXT: \subdir\x.h
 // File x.h must appear only once (case insensitive check).
 // CHECK-NOT: {{\\|/}}{{x|X}}.{{h|H}}
 

clang/test/VFS/external-names.c

@@ -47,4 +47,4 @@
 
 // RUN: %clang_cc1 -D REINCLUDE -I %t -ivfsoverlay %t.yaml -Eonly %s -MTfoo -dependency-file %t.dep
 // RUN: cat %t.dep | FileCheck --check-prefix=CHECK-DEP %s
-// CHECK-DEP-NOT: Inputs
+// CHECK-DEP: Inputs{{..?}}external-names.h