happstack-data-6.0.1, happstack-state-6.1.3: improved GHC 7.4 support

[Jeremy Shaw]

Hello,

I just uploaded happstack-data-6.0.1 and happstack-state-6.1.3. GHC 7.4 ships with the new base >= 4.4.

In base >= 4.4 the show instance for TypeRep stopped producing fulling qualified names. This affects happstack-state because we store those names in the checkpoint file.

This meant that if you build your app with base < 4.4 and the rebuilt with  base >= 4.4, happstack-state would not be able to find any of the components in your checkpoint file, or replay any events.

The new version uses a new function, showQualifiedTypeRep for base >= 4.4 which ensures backwards compatibility.

It did some basic testing and it seems to work fine -- but I would recommend making sure your backups are intact before upgrading just in case.

- jeremy

[dag.od...@gmail.com]

Does this affect acid-state too? At least openLocalState should be
affected right?

[Jeremy Shaw]

acid-state should be affected, though to a lessor degree.

 1. the name generated by openLocalState will change. This can be worked around by renaming the state directories on the disk or by using openLocalStateFrom

 2. the event names in the events file will also change. This can be worked around by creating a checkpoint before upgrading so that no old events need to be replayed

There is also now a new possible issue that could arise. If you use openLocalState from on two types that have the same name but come from different modules, then they will both end up in the same state directory (causing a mess). Or perhaps openLocalState has some sort of locking mechanism that prevents that?

In any case, I am not sure if any of these issues warrant making a change to acid-state since they user can work-around all of them. (That was not the case with happstack-state). 

If we leave acid-state as-is, we should at least make a note of the issues and the workarounds.

- jeremy

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