feat: allow self renamer to work if tempdir is on a different device

[davidkna]

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• The PR title is descriptive.
• I have read CONTRIBUTING.md
• The code compiles (cargo build)
• The code passes rustfmt (cargo fmt)
• The code passes clippy (cargo clippy)
• The code passes tests (cargo test)
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Currently, the self renamer fails with the following error if the tempdir is on a different device from the system temporary directory:

Error:
   0: The system cannot move the file to a different disk drive. (os error 17)

This PR works around this by using a temporary file in the binary directory instead in that case.

If you developed a feature or a bug fix for someone else and you do not have the
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.29%. Comparing base (4d66431) to head (b4372ee).

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #797      +/-   ##
========================================
- Coverage   6.81%   2.29%   -4.52%     
========================================
  Files         37      30       -7     
  Lines      11820    4566    -7254     
========================================
- Hits         806     105     -701     
+ Misses     11014    4461    -6553     

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[SteveLauC]

Hi, thanks for your contributing to Topgrade!

I wonder can we do std::fs::copy(); std::fs::remove_file() here?

[davidkna]

I wonder can we do std::fs::copy(); std::fs::remove_file() here?

It would be possible to use this, but std::fs::rename() is something of a atomic operation which helps avoid issues around concurrent access and possibly mangling files.

[SteveLauC]

Yeah, that is one benefit of rename().

May I step back a little bit, and ask you what is the functionality of this SelfRenamer, I have never used the self-update feature and I am not the author of that code.

From my understanding, the renamer itself is simply doing a round-trip, I do not quite get why it is necessary on Windows.

[davidkna]

@SteveLauC The self-renamer is supposed to make self-upgrades on Windows work because executable files are locked while they are running and cannot be changed. That likely means that remove_file would not work in this case.

Looking at the surrounding code, this doesn't clean up the old executable on exit in the case of upgrade. With this new case using the binary directory, leaving the temporary executable in-place should be avoided, so I will convert this PR to a draft.

[davidkna]

Executable cleanup is now implemented via the self-replace crate that was already a transitive dependency via self_update.

The clippy issues seem to be unrelated, but I can add fixes for those if preferred.