Have builderv2 fetch itself

[DemiMarie]

This is accomplished by symlinking artifacts/sources/builderv2 to the toplevel directory.

THIS MIGHT WIPE DATA. DO NOT USE UNTIL REVIEWED.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.69%. Comparing base (e1bdbcd) to head (37dcf72).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
+ Coverage   74.13%   78.69%   +4.56%     
==========================================
  Files          47       47              
  Lines        5370     5370              
==========================================
+ Hits         3981     4226     +245     
+ Misses       1389     1144     -245     

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[marmarek]

This is interesting idea, but it won't work reliably. I see at least two issues:

• the artifacts dir is configurable, so the symlink won't work if non-default artifacts dir is used.
• in default configuration (git-run-inplace: false) the symlink probably will get removed

But even without those issues, self-updating is more problematic. You can't just update itself in the middle of some operation. Imagine for example fetching all components - as soon as builderv2 component is fetched, all builder's files will get updated (including for example scripts in qubesbuilder/plugins/fetch/scripts/). The new version may be not compatible with already running python code. The update needs to be performed separately (either as the only operation, or at least the last one).

[DemiMarie]

This is interesting idea, but it won't work reliably.

Extremely unsurprising. I added that comment for a reason 😆.

I see at least two issues:

• the artifacts dir is configurable, so the symlink won't work if non-default artifacts dir is used.
• in default configuration (git-run-inplace: false) the symlink probably will get removed

But even without those issues, self-updating is more problematic. You can't just update itself in the middle of some operation. Imagine for example fetching all components - as soon as builderv2 component is fetched, all builder's files will get updated (including for example scripts in qubesbuilder/plugins/fetch/scripts/). The new version may be not compatible with already running python code. The update needs to be performed separately (either as the only operation, or at least the last one).

Could the update be done by replacing a symlink followed by sys.exit(0)? That’s atomic.