[clang] In DependencyCollector on Windows, ignore case and separators when discarding duplicate dependency file paths.

This patch removes duplicates also encountered in the output of clang-scan-deps when one same header file is encountered with different casing and/or different separators ('/' vs '\').

The case of separators can appear when the same file is included externally by
 `#include <folder/file.h>`

whereas a file from the same folder does
 `#include "file.h"`

Under Windows, clang computes the paths using '/' from the include directive, the `\` from the -I options, and the concatenations use the native `\`, leading to internal paths containing a mix of both separators.

Differential Revision: https://reviews.llvm.org/D102339

1 files changed, 12 insertions, 1 deletions

diff --git a/clang/lib/Frontend/DependencyFile.cpp b/clang/lib/Frontend/DependencyFile.cpp
index ccc7ed9..2888273 100644
--- a/clang/lib/Frontend/DependencyFile.cpp
+++ b/clang/lib/Frontend/DependencyFile.cpp
@@ -141,7 +141,18 @@ void DependencyCollector::maybeAddDependency(StringRef Filename,
 }
 
 bool DependencyCollector::addDependency(StringRef Filename) {
-  if (Seen.insert(Filename).second) {
+  StringRef SearchPath;
+#ifdef _WIN32
+  // Make the search insensitive to case and separators.
+  llvm::SmallString<256> TmpPath = Filename;
+  llvm::sys::path::native(TmpPath);
+  std::transform(TmpPath.begin(), TmpPath.end(), TmpPath.begin(), ::tolower);
+  SearchPath = TmpPath.str();
+#else
+  SearchPath = Filename;
+#endif
+
+  if (Seen.insert(SearchPath).second) {
     Dependencies.push_back(std::string(Filename));
     return true;
   }