[PATCH] Support case insensitive header searches for MSVCCompat

[Richard Smith]

  Have you considered using something ilke [ciopfs](http://www.brain-dump.org/projects/ciopfs/)? =)

  This patch needs testcases.

  I also suspect that some of this belongs in LLVM's Support library, rather than here, but that can wait until we've figured out exactly what we want.


================
Comment at: lib/Lex/HeaderSearch.cpp:36-42
@@ +35,9 @@
+
+  for (PI = llvm::sys::path::rbegin(LowerPath),
+       PE = llvm::sys::path::rend(LowerPath),
+       FI = llvm::sys::path::rbegin(LowerFilename),
+       FE = llvm::sys::path::rend(LowerFilename);
+       FI != FE && PI != PE; ++PI, ++FI)
+    if (FI->str() != PI->str())
+      return false;
+
----------------
Do you need to compare anything other than the last component here?

================
Comment at: lib/Frontend/InitHeaderSearch.cpp:679
@@ -673,3 +678,3 @@
                                      const llvm::Triple &Triple) {
-  InitHeaderSearch Init(HS, HSOpts.Verbose, HSOpts.Sysroot);
+  InitHeaderSearch Init(HS, HSOpts.Verbose, HSOpts.Sysroot, Lang.MSVCCompat);
 
----------------
We don't want to pay the cost of this if the underlying file system is already case-insensitive. On Windows, `GetVolumeInformation` can be used to determine this. I don't think there's a good way to determine it for Linux, sadly.

(We should also use this in `FileManager` rather than making an assumption that Windows is case-insensitive and nothing else is there.)

================
Comment at: include/clang/Lex/DirectoryLookup.h:66
@@ +65,3 @@
+  /// \brief Whether the lookup should be case insensitive.  This is required
+  /// for compatibility with case-sensitive file systems and Mcirosoft mode
+  /// which does not include headers with the correct case.
----------------
Typo of "Microsoft"

================
Comment at: lib/Lex/HeaderSearch.cpp:257-265
@@ +256,11 @@
+    if (CaseInsensitive && !llvm::sys::fs::exists(TmpDir.str())) {
+      llvm::error_code EC;
+      std::string LowerFilename = Filename.lower();
+      for (llvm::sys::fs::directory_iterator DI(getDir()->getName(), EC), DE;
+           !EC && DI != DE; DI = DI.increment(EC)) {
+        if (IsEquivalent(DI->path(), LowerFilename)) {
+          TmpDir = DI->path();
+          break;
+        }
+      }
+    }
----------------
Please factor this out. Should you do something better with `EC` than ignoring it?


http://llvm-reviews.chandlerc.com/D2972