Windows path separators in `compile_commands.json` not parsed correctly

[Jeremy Day]

Windows path separators in compile_commands.json are not parsed correctly in splitShellEscapedCommand. Following the comment there to clang's unescapeCommandLine(), it seems clang has implemented Windows specific parsing.

There's a separate bug in Swift CMake that generates incorrect path separators on Windows, but after that is fixed I expect the entries in the compilation database to look like:

{
  "directory": "C:\\path\\to\\build",
  "command": "C:\\path\\to\\swiftc.exe <snip>,
  "file": "C:\\path\\to\\build\\filename.swift",
  "output": "path\\to\\filename.swift.obj"
}

These are single-escaped JSON backslashes, which are unescaped twice (once by JSON parsing, once in the function linked above), resulting paths like C:pathtobuildfilename.swift being passed to sourcekitd. If I manually change these paths in compile_commands.json to double-escaped backslashes (\\\\) or forward slashes, the paths are interpreted as expected.

[Alex Hoppen]

Tracked in Apple’s issue tracker as rdar://120809063