Attempt to replicate issue haskell/cabal#7466.

This is a Cabal project with an intricate dependency tree, but no source code. It was obfuscated using obfuscate.hs.

Run cabal clean followed by cabal build all --dry-run. The latter takes about 40 seconds locally to run, but is faster on subsequent runs. Switching between --enable-tests and --disable-test incurs this 40-second cost again.

cabal configure

% cabal clean
% cabal update
% time cabal configure
Resolving dependencies...
Build profile: -w ghc-8.10.4 -O1
...
cabal configure  43.40s user 9.81s system 52% cpu 1:42.08 total
% time cabal configure
'cabal.project.local' already exists, backing it up to 'cabal.project.local~'.
Build profile: -w ghc-8.10.4 -O1
...
cabal configure  7.67s user 2.02s system 54% cpu 17.941 total

cabal build all --dry-run

% cabal clean
% cabal update
% time cabal build all --dry-run
Resolving dependencies...
Build profile: -w ghc-8.10.4 -O1
...
cabal build all --dry-run  44.71s user 9.52s system 45% cpu 1:59.77 total
% time cabal build all --dry-run
Build profile: -w ghc-8.10.4 -O1
...
cabal build all --dry-run  8.51s user 2.14s system 56% cpu 18.757 total

Other considerations

• Deleting cabal.project.freeze and compare with that
• Use the master branch of the Cabal project

Package versions

• Cabal 3.4.0.0 (via ghcup)
• GHC 8.10.4 (via ghcup)

Workflow

In https://github.com/haskell/cabal,

cabal install cabal-install --overwrite-policy=always

The bug is reproduced by switching between enable-tests and disable-tests. In this repo, try

time ~/.cabal/bin/cabal build all --disable-tests --dry-run > disabled.log

and

time ~/.cabal/bin/cabal build all --enable-tests --dry-run > enabled.log

, then diff disabled.log enabled.log.

Also, try --verbose:

time ~/.cabal/bin/cabal build all --disable-tests --dry-run --verbose > disabled.log
time ~/.cabal/bin/cabal build all --enable-tests --dry-run --verbose > enabled.log

Print statements placed here https://github.com/haskell/cabal/blob/ec3cf26ae6021b7ca9f496a39efbcba50e459015/cabal-install/src/Distribution/Client/ProjectPlanning.hs#L413-L416 indicate that the improved-plan https://github.com/haskell/cabal/blob/ec3cf26ae6021b7ca9f496a39efbcba50e459015/doc/nix-local-build.rst#caching changes, triggering the 30~40 second resolver.

My results using Cabal 3.4

From disabled tests to enabled tests

cabal build all --disable-tests --dry-run > disabled.log
1.50s user 0.15s system 99% cpu 1.655 total

cabal build all --enable-tests --dry-run > enabled.log 
30.89s user 0.79s system 99% cpu 31.790 total

See disabled_to_enabled.diff.

From enabled tests to disabled tests

cabal build all --enable-tests --dry-run > enabled.log  
1.90s user 0.20s system 100% cpu 2.108 total

cabal build all --disable-tests --dry-run > disabled.log  
29.72s user 0.85s system 99% cpu 30.668 total

See enabled_to_disabled.diff.

The message "cannot read state cache" is of interest. The message is defined here: https://github.com/haskell/cabal/blob/ec3cf26ae6021b7ca9f496a39efbcba50e459015/cabal-install/src/Distribution/Client/ProjectOrchestration.hs#L954-L955