paths in options parsed incorrectly on windows

[dvyukov]

Originally reported at golang/go#22756
It seems that we mishandle : in full windows paths in options.

[eugenis]

Ouch :)
That's an unfortunate choice of option separator.
We could

• not treat ":" as a separator on windows. This could be confusing.
• not treat ":" followed by "" as a separator. This could also be confusing.
• any other ideas?

[dvyukov]

Special case : in flags that meant to contain paths if the value starts with [a-zA-Z]:\\.

[rnk]

Everyone hits this when moving their existing sanitizer testing wrapper from Posix to Windows. It's really annoying.

Maybe the special case could only apply after =, as in =[a-zA-Z]:[/\\], since usually the paths are the entire option.

[eugenis]

option names never start with \, it should be fine to special case any : immediately preceding that.

Stupid github lost the backslash character in my previous commit.

[rnk]

I assume option names also don't start with /. I'd like to keep that in the special case (if that's what we're doing) because it helps avoid these kinds of escaping problems.

[morehouse]

Any progress on this?

[rnk]

https://reviews.llvm.org/D48052