Stabilize Windows FileTypeExt with is_symlink_dir and is_symlink_file

[joshtriplett]

These calls allow detecting whether a symlink is a file or a directory,
a distinction Windows maintains, and one important to software that
wants to do further operations on the symlink (e.g. removing it).

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r? @thomcc

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[joshtriplett]

These methods didn't have a tracking issue.

[thomcc]

Impl looks fine, r=me once fcp happens

[ChrisDenton]

I would definitely love this to be stable.

---

This is not necessarily a problem but I thought it might be worth pointing out the difference between stdlib semantics and Windows semantics here. For example, if you want to know if a file is some kind of directory then you'd do:

file.is_dir() || file.is_symlink_dir()

Which ends up roughly translating to:

file.is_directory() && (!file.is_symlink() || file.is_symlink())

Presumably this is optimized to file.is_directory() or if not then it doesn't matter too much anyway. As I said, I'm only mentioning it because it highlights the difference in semantics.

[joshtriplett]

@ChrisDenton That seems reasonable. I think we'd get much more confusing results if is_dir returned true on a symlink.

[joshtriplett]

@rfcbot merge

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Team member @joshtriplett has proposed to merge this. The next step is review by the rest of the tagged team members:

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• @dtolnay
• @joshtriplett
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• @yaahc

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[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[joshtriplett]

@bors r=thomcc

[bors]

📌 Commit a4cb0b9 has been approved by thomcc

It is now in the queue for this repository.