Default implementation for a type class function missing when profiling is enabled

[JohnWiegley]

I tried to reduce this to a simpler case, but was unable to produce the bug.

At the following line you'll see the function loadObject' defined for the type class Updatable:

 https://github.com/fpco/gitlib/blob/master/gitlib/Data/Git/Internal.hs#L115

And on this line I create an instance of the Updatable type class, with no override for this function:

 https://github.com/fpco/gitlib/blob/master/gitlib/Data/Git/Blob.hs#L47

All is well until I build with profiling, as follows:

    cabal configure                             \
        --enable-tests                          \
        --enable-benchmarks                     \
        --enable-library-profiling              \
        --enable-executable-profiling           \
        --ghc-option=-rtsopts                   \
        --ghc-option=-prof                      \
        --ghc-option=-fprof-auto                \
        --ghc-option=-fprof-auto-calls
    cabal build

When built with profiling, the linker thinks that Blob.hs is trying to call another version of loadObject', _gitlibzm0zi5zi3_DataziGitziInternal_loadObjectzq_C1h_cc, which is not defined anywhere. The default implementation in the type class definition is named _gitlibzm0zi5zi3_DataziGitziInternal_loadObjectzq_C1g_cc.

The happens with both 7.4.2 and 7.6.1.

[simonpj]

Urgh. So many dependencies! Can you:

• Do ghc --show-iface on Data/Git/Internal.hi
• Compile Data.Git.Internal with -ddump-simpl
• Compile Data.Git.Blob with -ddump-ds -ddump-simpl

and let me have the output? thanks.

Simon

[ezyang]

GitHub? links no longer work!

[JohnWiegley]

The code has now moved on enough that it's going to be very hard to reproduce this. The best I can suggest is to clone the project and look back for a commit around the same date as this bug report. Or, just close this bug and see if someone else runs into it.

[simonpj]

OK, I think I'll just close it then. Sorry!