error with forward slashes in linter plugin on windows

[sprogma]

I wanted to create custom linter for my file format, and found that linter plugin doesn't support "/" in file paths on windows (matches %f in linter format string)

I think it's because of basename function (in runtime/plugins/linter/linter.lua), where sep is defined as "\\" on windows. Perhaps it should be "[/\\]"?

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This error doesn't happen with default C linters since clang and gcc don't change path format, so

clang a/b\c/../c/d.c -fsyntax-only

produces same pattern, and basename matches:

a/b\c/../c/d.c:1:1 error: ...

But i think some other linters can normalize path in error messages (as my linter does).