fix(metro-file-map): Fix Windows cross-device path resolution

[kitten]

Summary

Related PR for expo/expo fork: expo/expo#45648
Supersedes #1696

Cross-device path normals are intended to be relative paths from the rootDir. If the rootDir is at C:\project then a cross-device normal path at D:\temp is represented as ..\..\D:\temp. This assumption is broken in several places, like normalToAbsolute printing, leading to C:\D:\ paths that are invalid.

Changelog: [Fix] Fix Windows path handling for cross-drive paths

Test plan

• Unit tests were adjusted to demonstrate all failing cases
• Note: Invalid unit tests have been removed for paths that rise above the filesystem root (they're assumed to be impossible, and their output doesn't have to be deterministic/correct)

[meta-codesync]

@CalixTang has imported this pull request. If you are a Meta employee, you can view this in D104700077.

[robhogan]

Thanks again for looking at this!

Invalid unit tests have been removed for paths that rise above the filesystem root (they're assumed to be impossible, and their output doesn't have to be deterministic/correct)

This is very edge-casey but the behaviour of .. at the root is actually specified (at least on posix), those test cases weren't invalid or accidental.

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13

The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.

In particular, if you create a symlink with the target ../../../../file-at-root.txt at /, it will deference to /file-at-root.txt on posix, so it should with Metro as well.

[robhogan]

(Also, nit: device != drive. These are cross-drive paths)

[kitten]

interesting! that's an easy fix, but requires us to use startsWithDriveLetter (as per expo/expo#45648) in one place, I believe, so it's a bit of a trade-off. I didn't measure performance in that case, but I think it might not be otherwise possible to differentiate between the Windows/Posix root case otherwise. Although, I could be mistaken and there could be an easier way, if we ignore this case for Windows.

[meta-codesync]

@CalixTang merged this pull request in 6e6b52c.