[GHC] #1853: hpc mix files for Main modules overwrite each other

[GHC]

#1853: hpc mix files for Main modules overwrite each other
----------------------------------+--------------------------------------
        Reporter:  guest          |                Owner:
            Type:  bug            |               Status:  new
        Priority:  lowest         |            Milestone:  8.0.1
       Component:  Code Coverage  |              Version:  6.8.1
      Resolution:                 |             Keywords:
Operating System:  Linux          |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown   |            Test Case:
      Blocked By:                 |             Blocking:
 Related Tickets:                 |  Differential Rev(s):
       Wiki Page:                 |
----------------------------------+--------------------------------------

Comment (by mgsloan):

 Hi, thanks for the response Andy!

 Handily, I already had a minimal repro for this from back when I initially
 started working on coverage support in stack: https://github.com/mgsloan
 /multi-test-suite

 In particular:

 {{{
 mgsloan at computer:~/fpco/multi-test-suite$ cabal test --ghc-options -fhpc
 # ...mgsloan at computer:~/fpco/multi-test-suite$ hpc report multi-test-
 suite-test.tix
 hpc: can not find Main in ["./.hpc"]
 mgsloan at computer:~/fpco/multi-test-suite$ hpc report multi-test-suite-
 test-2.tix
  50% expressions used (1/2)
 100% boolean coverage (0/0)
      100% guards (0/0)
      100% 'if' conditions (0/0)
      100% qualifiers (0/0)
 100% alternatives used (0/0)
 100% local declarations used (0/0)
 100% top-level declarations used (1/1)
 }}}

 This issue will also affect cabal files that have other stanzas like
 executables and benchmarks.  I added a folder called sub-package to multi-
 test-repo, actually debug / test out a different stack coverage related
 issue.

 The only reasonable way I can think of to fix this is to add a flag to
 GHC, which takes the name to use for the mix file folder.  This won't
 directly fix the problem with current Cabal, but it would allow future
 version of Cabal to pass the info so that this issue is resolved.

 I'm not sure what to call the flag - it doesn't necessarily need to be
 specific to HPC - since there might be other places in GHC that benefit
 from knowing the cabal component.  So, I'm thinking either `-component-
 name`, or `-hpc-component-name`.

 I took a look at Cabal's current invocations of GHC to see if there is any
 way for GHC to know that it's building a particular executable component.
 Unfortunately, I don't see any arguments that would make a good source for
 this info:

 {{{
 /usr/local/bin/ghc --make -no-link -fbuilding-cabal-package -O -j8 -static
 -outputdir dist/build/multi-test-suite-test/multi-test-suite-test-tmp
 -odir dist/build/multi-test-suite-test/multi-test-suite-test-tmp -hidir
 dist/build/multi-test-suite-test/multi-test-suite-test-tmp -stubdir
 dist/build/multi-test-suite-test/multi-test-suite-test-tmp -i -idist/build
 /multi-test-suite-test/multi-test-suite-test-tmp -itest
 -idist/build/autogen -Idist/build/autogen -Idist/build/multi-test-suite-
 test/multi-test-suite-test-tmp -optP-include
 -optPdist/build/autogen/cabal_macros.h -hide-all-packages -package-db
 dist/package.conf.inplace -package-id
 base-4.8.1.0-4f7206fd964c629946bb89db72c80011 -package-id multi-test-
 suite-0.1.0.0-inplace -XHaskell2010 test/Spec.hs -threaded -rtsopts
 '-with-rtsopts=-N' -fhpc
 }}}

 (Sorry, the naming isn't all that clear, `multi-test-suite-test` is the
 name of the component)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1853#comment:23>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler