ExitFailure 1 on `Hat` again

Question

In this question, we installed the dependencies for Hat. Now when I try to do

cabal install Hat

I get at the end:

[ 6 of 11] Compiling Environment      ( trans/Environment.hs, dist/build/hat-trans/hat-trans-tmp/Environment.o )

trans/Environment.hs:497:13:
    Not in scope: data constructor `PExplTypeArg'
Failed to install hat-2.8.0.0
World file is already up to date.
cabal: Error: some packages failed to install:
hat-2.8.0.0 failed during the building phase. The exception was:
ExitFailure 1

Answer 1

Hat depends on an old version of haskell-src-exts. The constructor in question appears to have disappeared in version 1.14.

You can edit the file, deleting the offending line and submit a patch to Hat. Alternatively, specify and extra constraint:

cabal install hat --constraint haskell-src-exts==1.13.5

In the future, you can trace these sorts of issues down by yourself by looking at the package dependencies, find the module that contains the type in question, and look for the constructor. This particular case is really googlable too.