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

[sammccall]

Summary

Since D60873 we remove dotdots from the search path entries, but not the
filenames we're matching against, so do the latter too.

Since this also removes (single) dots, drop the logic to skip over them.
(Some of this was already dead, some is newly dead).

See D138676 for motivation.

[kadircet]

clang/lib/Lex/HeaderSearch.cpp

1932

nit: you can change the method signature to take in a SmallString directly. there's an implicit constructor and any caller that already has a copy that they're throwing away can pass it here instead.

1932

this is same as llvm::SmallString<32> FilePath(File);

1948

looks like reflow went wrong here, drop //?

[sammccall]

clang/lib/Lex/HeaderSearch.cpp

1932

I don't think this is a good reason to change the signature unless it's actually a hot path.
(In fact, no caller has a SmallString<32>).

I changed CheckDir though because it's internal.

[thakis]

This breaks tests on windows: http://45.33.8.238/win/70650/step_7.txt

Please take a look and revert for now if it takes a while to fix.

clang/lib/Lex/HeaderSearch.cpp

std::string HeaderSearch::suggestPathToFileForDiagnostics(
   return suggestPathToFileForDiagnostics(File->getName(), /*WorkingDir=*/"",
                                          MainFile, IsSystem);
 }
 
 std::string HeaderSearch::suggestPathToFileForDiagnostics(
     llvm::StringRef File, llvm::StringRef WorkingDir, llvm::StringRef MainFile,
     bool *IsSystem) {
   using namespace llvm::sys;
   
+  llvm::SmallString<32> FilePath = File;
+  path::remove_dots(FilePath, /*remove_dot_dot=*/true);
+  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;
           return true;
         }
         break;
       }
 

clang/unittests/Lex/HeaderSearchTest.cpp

 TEST_F(HeaderSearchTest, DotDotsWithAbsPath) {
   addSearchDir("/x/../y/");
   EXPECT_EQ(Search.suggestPathToFileForDiagnostics("/y/z",
                                                    /*WorkingDir=*/"",
                                                    /*MainFile=*/""),
             "z");
 }
 
+TEST_F(HeaderSearchTest, BothDotDots) {
+  addSearchDir("/x/../y/");
+  EXPECT_EQ(Search.suggestPathToFileForDiagnostics("/x/../y/z",
+                                                   /*WorkingDir=*/"",
+                                                   /*MainFile=*/""),
+            "z");
+}
+
 TEST_F(HeaderSearchTest, IncludeFromSameDirectory) {
   EXPECT_EQ(Search.suggestPathToFileForDiagnostics("/y/z/t.h",
                                                    /*WorkingDir=*/"",
                                                    /*MainFile=*/"/y/a.cc"),
             "z/t.h");
 
   addSearchDir("/");
   EXPECT_EQ(Search.suggestPathToFileForDiagnostics("/y/z/t.h",