macOS fails to install dependencies: Could not symlink lib/libtcl8.6.dylib

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The macOS CI of GitHub Action failed in the Install Homebrew dependencies step with:

Linking /usr/local/Cellar/tcl-tk@8/8.6.16... 
Error: Could not symlink lib/libtcl8.6.dylib
Target /usr/local/lib/libtcl8.6.dylib
is a symlink belonging to tcl-tk@8. You can unlink it:
  brew unlink tcl-tk@8

To force the link and overwrite all conflicting files:
  brew link --overwrite tcl-tk@8

To list all files that would be deleted:
  brew link --overwrite tcl-tk@8 --dry-run

cc @hugovk @ambv

Linked PRs

• gh-128069: Do not manually brew link Tcl/Tk to fix macOS CI failure #128082
• gh-128069: brew link --overwrite tcl-tk@8 to prevent conflict with GitHub image's version #128090
• [3.13] gh-128069: brew link --overwrite tcl-tk@8 to prevent conflict with GitHub image's version (GH-128090) #128096
• [3.12] gh-128069: brew link --overwrite tcl-tk@8 to prevent conflict with GitHub image's version (GH-128090) #128125
• [3.11] gh-128069: brew link --overwrite tcl-tk@8 to prevent conflict with GitHub image's version (GH-128090) #129172

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I saw the failure on macos-13 image version 20241216.479 (2024-12-16):

2024-12-18T12:57:14.6389370Z ##[group]Runner Image
2024-12-18T12:57:14.6389940Z Image: macos-13
2024-12-18T12:57:14.6390470Z Version: 20241216.479
2024-12-18T12:57:14.6391690Z Included Software: https://github.com/actions/runner-images/blob/macos-13/20241216.479/images/macos/macos-13-Readme.md
2024-12-18T12:57:14.6393460Z Image Release: https://github.com/actions/runner-images/releases/tag/macos-13%2F20241216.479
2024-12-18T12:57:14.6394560Z ##[endgroup]

2024-12-18T12:57:14.6395090Z ##[group]Runner Image Provisioner
2024-12-18T12:57:14.6395820Z 2.0.404.1+573eac7f0cc07d6bb82d8b9bf5e1ffa69a554644
2024-12-18T12:57:14.6396560Z ##[endgroup]

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I saw the failure on macos-13 image version 20241216.479

The job pass with macos-13 image version 20241211.456 (2024-12-11).

[hugovk]

Yes:

Pass: https://github.com/python/cpython/actions/runs/12389079636/job/34581414776

2024-12-18T08:26:15.6290250Z Version: 20241211.456
2024-12-18T08:26:15.6291590Z Included Software: https://github.com/actions/runner-images/blob/macos-13/20241211.456/images/macos/macos-13-Readme.md
2024-12-18T08:26:15.6293490Z Image Release: https://github.com/actions/runner-images/releases/tag/macos-13%2F20241211.456
...
2024-12-18T08:26:39.4338960Z Linking /usr/local/Cellar/tcl-tk@8/8.6.15... 1753 symlinks created.
2024-12-18T08:26:39.4340050Z 

Fail: https://github.com/python/cpython/actions/runs/12389598892/job/34582962458

2024-12-18T09:00:08.6363650Z Version: 20241216.479
2024-12-18T09:00:08.6365420Z Included Software: https://github.com/actions/runner-images/blob/macos-13/20241216.479/images/macos/macos-13-Readme.md
2024-12-18T09:00:08.6368470Z Image Release: https://github.com/actions/runner-images/releases/tag/macos-13%2F20241216.479
...
2024-12-18T09:00:41.8750860Z Linking /usr/local/Cellar/tcl-tk@8/8.6.16... 
2024-12-18T09:00:41.8783970Z ##[error]Could not symlink lib/libtcl8.6.dylib
Target /usr/local/lib/libtcl8.6.dylib
is a symlink belonging to tcl-tk@8. You can unlink it:
  brew unlink tcl-tk@8

To force the link and overwrite all conflicting files:
  brew link --overwrite tcl-tk@8

[hugovk]

The Tcl/Tk version changed from 8.6.15 to 8.6.16 in the GH image.

#127365 added the Homebrew tcl-tk@ pin to prevent Homebrew installing version 9.

https://formulae.brew.sh/formula/tcl-tk@8 says it's also on 8.6.16.

Perhaps we should try the --overwrite?

[hugovk]

That installs and passes:

Linking /usr/local/Cellar/tcl-tk@8/8.6.15... 1753 symlinks created.

If you need to have this software first in your PATH instead consider running:
  echo 'export PATH="/usr/local/opt/tcl-tk@8/bin:$PATH"' >> /Users/runner/.bash_profile

hugovk@439a329

https://github.com/hugovk/cpython/actions/runs/12395563219/job/34601604141

[ZeroIntensity]

It might be worth temporarily disabling the job while this gets figured out. Many PRs are stuck because of this.

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That installs and passes: (...)
hugovk@439a329

I created a PR for this commit: #128090.