hpc: Improve error messages in readMix

See https://hackage.haskell.org/package/hpc-0.6.0.2/docs/src/Trace-Hpc-Mix.html#readMix

The generic error $ "can not find " ++ modName ++ " in " ++ show dirNames error message is used for all kinds of cases, for example when h == tixModuleHash tix isn't true.

It would be very helpful if the error message could be specific for these cases (e.g. "hashes don't agree") instead of being a catch-all for all Nothings.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Code Coverage
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	nh2
Operating system
Architecture

changed weight to 5

added HPC Tbug Trac import labels

I have a patch here: https://github.com/ghc/packages-hpc/commit/eaf1906f4456765becd3b52dee0188750feab2bf

The error messages would look like this now:

hpc: can not parse ./.hpc/NoParse.mix

hpc: hash in .tix file does not match hash in ./.hpc/Main.mix

hpc: can not find NonExistingModule in ["./.hpc"]

nh2: does that look alright to you?

@thomie, yes that looks good to me. The only thing I'd change is adding more detail to the error message, e.g. mentioning the modName and what the values of the two hashes are that aren't matching - that makes it much easier to debug what's wrong when something is wrong.

I'll also add a comment on Github for this.

Thanks for the quick fix, much appreciated!

Updated patch: https://github.com/ghc/packages-hpc/commit/6b88e91c8a0e7806d44d999616983c60a0b8eb78

Now you'll get something like this:

hpc: hash in tix file for module Main (1234567890)
does not match hash in ./.hpc/Main.mix (2454134535)

Yes that looks great to me!

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ simple/tixs/T10529{a,b,c}

mentioned in commit b4ef8b8b

changed milestone to %8.0.1

Milestone renamed

mentioned in issue #10951

added Pnormal label