Make -Wnonportable-include-path ignore drive case on Windows.

[thakis]

Summary

See PR45812 for motivation.

No explicit test since I couldn't figure out how to get the
current disk drive in lower case into a form in lit where I could
mkdir it and cd to it. But the change does have test coverage in
that I can remove the case normalization in lit, and tests failed
on several bots (and for me locally if in a pwd with a lower-case
drive) without that normalization prior to this change.

[rnk]

clang/lib/Lex/PPDirectives.cpp

2118

It seems like trySimplifyPath could check if it is checking the case of the first component on Windows, and that would hide the complexity from the main Preprocessor::HandleHeaderIncludeOrImport implementation. It also saves a string copy for every include.

[thakis]

clang/lib/Lex/PPDirectives.cpp

2118

Not easily, since that walks the path backwards. Includes are almost never absolute, so this also almost never does a string copy and it's imho a bit simpler this way.

I agree pulling out the code for this warning into its own function is a good idea though.

[hans]

Looks reasonable to me, but Windows paths are scary..

clang/lib/Lex/PPDirectives.cpp

2112

Maybe expand "was used" to "was used in the shell" or something. It may not be clear for people without context, since this whole thing is pretty obscure.

2123

Could it be different for e.g. network drives? I guess maybe they'd still have at least 3 components, but perhaps no drive letter

[thakis]

clang/lib/Lex/PPDirectives.cpp

2123

Oh, good call, /FI\\?\%cd%\test.h produces a path that's is_absolute() but that returns

\\?
\
c:
\
src
llvm-project
test.h

as path components (one per line). Looking at how to handle that now. If anyone happens to know, please shout :)

[thakis]

Landed in d03838343f2199580. Found another bug elsewhere while looking at this, will make a patch for that now.

clang/lib/Lex/PPDirectives.cpp

2123

This now strips the common UNC path at the start and restores it at the end if it was there, and there's a test for this.

clang/lib/Lex/PPDirectives.cpp

#endif
   const bool CheckIncludePathPortability =
       !IsMapped && !File->getFileEntry().tryGetRealPathName().empty();
 
   if (CheckIncludePathPortability) {
     StringRef Name = LookupFilename;
     StringRef RealPathName = File->getFileEntry().tryGetRealPathName();
     SmallVector<StringRef, 16> Components(llvm::sys::path::begin(Name),
                                           llvm::sys::path::end(Name));
+#if defined(_WIN32)
+    // -Wnonportable-include-path is designed to diagnose includes using
+    // case even on systems with a case-insensitive file system.
+    // On Windows, RealPathName always starts with an upper-case drive
+    // letter for absolute paths, but Name might start with either
+    // case depending on if `cd c:\foo` or `cd C:\foo` was used.
+    // ("foo" will always have on-disk case, no matter which case was
+    // used in the cd command). To not emit this warning solely for
+    // the drive letter, whose case is dependent on if `cd` is used
+    // with upper- or lower-case drive letters, always consider the
+    // given drive letter case as correct for the purpose of this warning.
+    SmallString<128> FixedDriveRealPath;
+    if (llvm::sys::path::is_absolute(Name) &&
+        llvm::sys::path::is_absolute(RealPathName) &&
+        toLowercase(Name[0]) == toLowercase(RealPathName[0]) &&
+        isLowercase(Name[0]) != isLowercase(RealPathName[0])) {
+      assert(Components.size() >= 3 && "should have drive, backslash, name");
+      FixedDriveRealPath = (Name.substr(0, 1) + RealPathName.substr(1)).str();
+      RealPathName = FixedDriveRealPath;
+    }
+#endif
 
     if (trySimplifyPath(Components, RealPathName)) {
       SmallString<128> Path;
       Path.reserve(Name.size()+2);
       Path.push_back(isAngled ? '<' : '"');
 
       const auto IsSep = [BackslashStyle](char c) {
         return llvm::sys::path::is_separator(c, BackslashStyle);

llvm/cmake/modules/AddLLVM.cmake

string(CONCAT LLVM_LIT_PATH_FUNCTION
   # loading the config. This causes __file__ to be all lower-case (including
   # the drive letter), but several clang tests pass -include %s and a
   # clang warning checks that passed case matches on-disk cache. So it's
   # important that this restores the on-disk case of the prefix.
   "# Allow generated file to be relocatable.\n"
   "def path(p):\n"
   "    if not p: return ''\n"
   "    p = os.path.join(os.path.dirname(os.path.abspath(__file__)), p)\n"
-  "    if os.name == 'nt' and os.path.isabs(p): return p[0].upper() + p[1:]\n"
   "    return p\n"
   )
 
 # This function provides an automatic way to 'configure'-like generate a file
 # based on a set of common and custom variables, specifically targeting the
 # variables needed for the 'lit.site.cfg' files. This function bundles the
 # common variables that any Lit instance is likely to need, and custom
 # variables can be passed in.