cabal install --enable-coverage doesn't install mix in findable location, causing hpc to fail when those ids are mentioned

[ezyang]

If we do this, then GHC will generate tix for those modules, but Cabal doesn't know how to find them:

ezyang@sabre:~/Dev/labs/map-syntax$ /opt/cabal/1.24/bin/cabal test -v
Component build order: test suite 'testsuite'
creating dist/build
creating dist/build/autogen
/usr/bin/ghc-pkg init dist/package.conf.inplace
Preprocessing test suite 'testsuite' for map-syntax-0.2.0.1...
Building test suite testsuite...
creating dist/build/testsuite
creating dist/build/testsuite/testsuite-tmp
/usr/bin/ghc --make -no-link -fbuilding-cabal-package -O -fhpc -hpcdir dist/hpc/vanilla/mix/testsuite -j1 -static -outputdir dist/build/testsuite/testsuite-tmp -odir dist/build/testsuite/testsuite-tmp -hidir dist/build/testsuite/testsuite-tmp -stubdir dist/build/testsuite/testsuite-tmp -i -idist/build/testsuite/testsuite-tmp -isrc -itest -idist/build/autogen -Idist/build/autogen -Idist/build/testsuite/testsuite-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -hide-all-packages -package-db dist/package.conf.inplace -package-id HUnit-1.3.0.0-904109a490c85ff643c14c4cfbe058fb -package-id QuickCheck-2.8.1-2cs6jeUUZX9ZLDN6ycKJHM -package-id base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d -package-id containers-0.5.6.2-59326c33e30ec8f6afd574cbac625bbb -package-id deepseq-1.4.1.1-614b63b36dd6e29d2b35afff57c25311 -package-id hspec-2.2.3-26H6GBDRpLQCyZpmHWBtcW -package-id mtl-2.2.1-378RFoja0lduCvzTAM9NPi -package-id transformers-0.4.2.0-81450cd8f86b36eaa8fa0cbaf6efc3a3 -XHaskell2010 test/TestSuite.hs -Wall -fwarn-tabs
[1 of 4] Compiling Data.Map.Syntax  ( src/Data/Map/Syntax.hs, dist/build/testsuite/testsuite-tmp/Data/Map/Syntax.o )
[2 of 4] Compiling Data.Map.Syntax.Util ( test/Data/Map/Syntax/Util.hs, dist/build/testsuite/testsuite-tmp/Data/Map/Syntax/Util.o )
[3 of 4] Compiling Data.Map.Syntax.Tests ( test/Data/Map/Syntax/Tests.hs, dist/build/testsuite/testsuite-tmp/Data/Map/Syntax/Tests.o )

test/Data/Map/Syntax/Tests.hs:10:1: Warning:
    The import of ‘Data.Monoid’ is redundant
      except perhaps to import instances from ‘Data.Monoid’
    To import instances alone, use: import Data.Monoid()
[4 of 4] Compiling Main             ( test/TestSuite.hs, dist/build/testsuite/testsuite-tmp/Main.o )
Linking...
/usr/bin/ghc --make -fbuilding-cabal-package -O -fhpc -hpcdir dist/hpc/vanilla/mix/testsuite -static -outputdir dist/build/testsuite/testsuite-tmp -odir dist/build/testsuite/testsuite-tmp -hidir dist/build/testsuite/testsuite-tmp -stubdir dist/build/testsuite/testsuite-tmp -i -idist/build/testsuite/testsuite-tmp -isrc -itest -idist/build/autogen -Idist/build/autogen -Idist/build/testsuite/testsuite-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -hide-all-packages -package-db dist/package.conf.inplace -package-id HUnit-1.3.0.0-904109a490c85ff643c14c4cfbe058fb -package-id QuickCheck-2.8.1-2cs6jeUUZX9ZLDN6ycKJHM -package-id base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d -package-id containers-0.5.6.2-59326c33e30ec8f6afd574cbac625bbb -package-id deepseq-1.4.1.1-614b63b36dd6e29d2b35afff57c25311 -package-id hspec-2.2.3-26H6GBDRpLQCyZpmHWBtcW -package-id mtl-2.2.1-378RFoja0lduCvzTAM9NPi -package-id transformers-0.4.2.0-81450cd8f86b36eaa8fa0cbaf6efc3a3 -XHaskell2010 test/TestSuite.hs -o dist/build/testsuite/testsuite -Wall -fwarn-tabs
Linking dist/build/testsuite/testsuite ...
Running 1 test suites...
Test suite testsuite: RUNNING...
dist/build/testsuite/testsuite
Test suite testsuite: PASS
Test suite logged to: dist/test/map-syntax-0.2.0.1-testsuite.log
/srv/prod/bin/hpc markup dist/hpc/vanilla/tix/testsuite/testsuite.tix '--destdir=dist/hpc/vanilla/html/testsuite' '--hpcdir=dist/hpc/vanilla/mix/testsuite' '--hpcdir=dist/hpc/vanilla/mix/map-syntax-0.2.0.1' '--exclude=Data.Map.Syntax' '--exclude=Data.Map.Syntax.Util' '--exclude=Data.Map.Syntax.Tests' '--exclude=Main'
hpc: can not find 5Dy4335KtNp12MnuUhJwf2/Test.Hspec.Timer in ./.hpc, ./dist/hpc/vanilla/mix/map-syntax-0.2.0.1, ./dist/hpc/vanilla/mix/testsuite
CallStack (from ImplicitParams):
  error, called at libraries/hpc/Trace/Hpc/Mix.hs:119:15 in hpc-0.6.0.2:Trace.Hpc.Mix

Originally discovered when trying to reproduce #3682

[ezyang]

Actually, maybe we should just install the mix files in this case? Basically, every package you enable coverage for should show up in the coverage report. That ought to work!

[ezyang]

We're not planning on fixing this unless it actually affects someone.

[cartazio]

@davean is this the problem we hit?

[Mikolaj]

This is superseded by #5213. If we fix this, it will be in v2- commands, not v1-. Closing