Reland "[Lex] Fix suggested spelling of /usr/bin/../include/foo"

This reverts commit 1dc0a1e5d220b83c1074204bd3afd54f3bac4270.

Failures were caused by unintentional conversion to native slashes by
remove_dots, so undo that: we always suggest posix slashes for includes.

This could potentially be a change in behavior on windows if people were
spelling headers with backslashes and headermaps contained backslashes,
but that's all underspecified and I don't think anyone uses headermaps
on windows.

Differential Revision: https://reviews.llvm.org/D138709

1 files changed, 13 insertions, 17 deletions

diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index e6af122..7bf278c 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -1928,32 +1928,28 @@ std::string HeaderSearch::suggestPathToFileForDiagnostics(
     llvm::StringRef File, llvm::StringRef WorkingDir, llvm::StringRef MainFile,
     bool *IsSystem) {
   using namespace llvm::sys;
+  
+  llvm::SmallString<32> FilePath = File;
+  // remove_dots switches to backslashes on windows as a side-effect!
+  // We always want to suggest forward slashes for includes.
+  // (not remove_dots(..., posix) as that misparses windows paths).
+  path::remove_dots(FilePath, /*remove_dot_dot=*/true);
+  path::native(FilePath, path::Style::posix);
+  File = FilePath;
 
   unsigned BestPrefixLength = 0;
   // Checks whether `Dir` is a strict path prefix of `File`. If so and that's
   // the longest prefix we've seen so for it, returns true and updates the
   // `BestPrefixLength` accordingly.
-  auto CheckDir = [&](llvm::StringRef Dir) -> bool {
-    llvm::SmallString<32> DirPath(Dir.begin(), Dir.end());
+  auto CheckDir = [&](llvm::SmallString<32> Dir) -> bool {
     if (!WorkingDir.empty() && !path::is_absolute(Dir))
-      fs::make_absolute(WorkingDir, DirPath);
-    path::remove_dots(DirPath, /*remove_dot_dot=*/true);
-    Dir = DirPath;
+      fs::make_absolute(WorkingDir, Dir);
+    path::remove_dots(Dir, /*remove_dot_dot=*/true);
     for (auto NI = path::begin(File), NE = path::end(File),
               DI = path::begin(Dir), DE = path::end(Dir);
-         /*termination condition in loop*/; ++NI, ++DI) {
-      // '.' components in File are ignored.
-      while (NI != NE && *NI == ".")
-        ++NI;
-      if (NI == NE)
-        break;
-
-      // '.' components in Dir are ignored.
-      while (DI != DE && *DI == ".")
-        ++DI;
+         NI != NE; ++NI, ++DI) {
       if (DI == DE) {
-        // Dir is a prefix of File, up to '.' components and choice of path
-        // separators.
+        // Dir is a prefix of File, up to choice of path separators.
         unsigned PrefixLength = NI - path::begin(File);
         if (PrefixLength > BestPrefixLength) {
           BestPrefixLength = PrefixLength;