lit: Let lit.util.which() return a normcase()ed path

[thakis]

Summary

LLVMConfig.with_environment() uses os.path.normcase(os.path.normpath(x)) to normalize temporary env vars. LLVMConfig.use_clang() uses with_environment() to temporarily set PATH and then look for clang there. This means that on Windows, clang will be run with a path like c:\foo\bin\clang.EXE (with a lower-case "C:").

lit.util.which() used to not do this, which means the executables added in clang/test/lit.cfg.py (e.g. c-index-test) were run with a path like C:\foo\bin\c-index-test.EXE (because both CMake and GN happen to write clang_tools_dir with an upper-case C to lit.site.cfg.py).

clang/test/Index/pch-from-libclang.c requires that both c-index-test and clang use _exactly_ the same resource dir path (same case and everything), because a hash of the resource directory is used as module cache path.

This patch is necessary but not sufficient to make pch-from-libclang.c pass on Windows.

[zturner]

Shouldn't the hash be case-insensitive on windows?

[thakis]

In D57343#1374063, @zturner wrote:

Shouldn't the hash be case-insensitive on windows?

I'm not sure: I think case-sensitive file systems on Windows are becoming more common with WSL. This seemed like the less intrusive change to me at least. If we make it case-insensitive on Win, we probably also want that on macOS, but there case-sensitive file systems also exist and are maybe more common, and it feels like a can of worms that I'd rather leave closed.

[thakis]

zturner: ping

[zturner]

I think it's possible to detect the case insensitivity of the file system itself, rather than relying on the operating system which as you point out is neither necessary nor sufficient to identify case insensitivity. But, also like you pointed out, that's another can of worms entirely, so I agree this is the simplest thing to make things better than before.

llvm/trunk/utils/lit/lit/util.py

def which(command, paths=None):
     """which(command, [paths]) - Look up the given command in the paths string
     (or the PATH environment variable, if unspecified)."""
 
     if paths is None:
         paths = os.environ.get('PATH', '')
 
     # Check for absolute match first.
     if os.path.isabs(command) and os.path.isfile(command):
-        return os.path.normpath(command)
+        return os.path.normcase(os.path.normpath(command))
 
     # Would be nice if Python had a lib function for this.
     if not paths:
         paths = os.defpath
 
     # Get suffixes to search.
     # On Cygwin, 'PATHEXT' may exist but it should not be used.
     if os.pathsep == ';':
         pathext = os.environ.get('PATHEXT', '').split(';')
     else:
         pathext = ['']
 
     # Search the paths...
     for path in paths.split(os.pathsep):
         for ext in pathext:
             p = os.path.join(path, command + ext)
             if os.path.exists(p) and not os.path.isdir(p):
-                return os.path.normpath(p)
+                return os.path.normcase(os.path.normpath(p))
 
     return None
 
 
 def checkToolsPath(dir, tools):
     for tool in tools:
         if not os.path.exists(os.path.join(dir, tool)):
             return False