Allow backslash after drive name

[weirdan]

Before, paths like C:/path/to/something were considered absolute, but C:\path/to/something were not

Refs #1913

[bdsl]

Do you want to revert 210ac39 as part of this PR?

[weirdan]

Perhaps, but it needs to pass on Appveyor first

[bdsl]

You won't see testPluginFilenameCanBeAbsolute pass on AppVeyor as things are, since 210ac39 stops that particular test running in any Windows environment.

But the latest commits seem to be failing on AppVeyor only for a different reason - Psalm is emitting two DuplicateClass errors when analysing itself there. See https://ci.appveyor.com/project/muglug/psalm/builds/25804844/job/q7c8vk3jle3r0686 . No idea why that happens in AppVeyor but not in Travis or CircleCI.

[weirdan]

One reason could be that psalm actually analyzes those files twice: as path\to\file.php and path/to/file.php (note the path separators). At least it's what it reports.

[muglug]

Thanks - I’ll fix those errors separately

[weirdan]

Is there a reason why Psalm uses its own isAbsolutePath() even though there's webmozart/path-util direct dependency (which includes a similar method)?

[muglug]

No - feel free to create a PR to fix that