[llvm-bugs] [Bug 41379] New: clang produces ambiguous .d files

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41379

            Bug ID: 41379
           Summary: clang produces ambiguous .d files
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: andrew at ziglang.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Zig runs clang in a child process with `-MD -MF foo.d` and then parses `foo.d`
to find out the list of dependencies of the compilation.

The problem is that with or without `-MV`, the format is ambiguous.

Without -MV, on Windows, I saw this example file:

C:\msys64\home\andy\dev\zig\example\shared_library\zig-cache\tmp\CHLssWPWWG0d-test.obj:
\
  C:\msys64\home\andy\dev\zig\example\shared_library\test.c \
  C:\msys64\home\andy\dev\zig\example\shared_library\zig-cache\mathtest.h \
  C:\Program\ Files\ (x86)\Microsoft\ Visual\
Studio\2017\Community\VC\Tools\MSVC\14.15.16726\lib\x64\\..\..\include\stdint.h
\
  ...

This is impossible to parse correctly - for example an escaped space is
indistinguishable from a path separator and then a space.

When I add `-MV`, the files are double-quote escaped, which fixes the issue.
However, `-MV` appears to not affect the "target", only the prerequisites. So
the problem remains for the target.

Downstream issue: https://github.com/ziglang/zig/issues/2046

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