Resolving dependencies is much slower for haskell.nix with lots of source-repository-package stanzas

[michaelpj]

Recording some debugging from elsewhere.

Some digging turned up haskell/cabal#7472.

It turns out this can hit haskell.nix much worse. With cabal 3.4, setting tests: true won't affect your source-repository-packages. But haskell.nix "inlines" them into local packages, so they will be affected.

This can massively amplify the impact of the cabal issue, causing solving to take many minutes.

[stale]

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