Hook redesign

[ezyang]

@ttuegel, let's make this a tracking ticket for hook redesign.

I'm collecting tickets of things that should be fixed in the redesign:

• Get LocalBuildInfo in pre-test hook #2599 - We should make LBI uniformly available to all hooks when it is available
• LocalBuildInfo should change at build time when components are selected #2910 - Hooks should operate on per-component level
• Proposal for a Cabal plugin API (inversion of control) #2395 - This was a proposal to invert control to external processes, so that you could add hooks without requiring a build against a version of Cabal
• Lessons learned from Custom #3065 - I wrote up some lessons I had learned from Custom
• install hook (Custom setup) is not called on Setup copy/register #1805 - install hook is redundant with copy/register hook
• localPkgDescr is frequently out-of-date #3606 - only the configure pre-hook should return a HookedLocalBuildInfo; the rest should not!
• Way to pass custom options to hook script #3625 - no way to pass custom arguments to hooks
• Revert Revert "Generalize HookedBuildInfo to work with any type of component." #3627 - HookedBuildInfo should support all different component types, not just library and executable

[dcoutts]

And remove things like the program db in some of the flag types which are there only to avoid modifying the hook function types. See the TODO in the code.

[fmaste]

Now with #3670 we can add a hook to generate the autogen-modules. The hook output could be Just Text and its input the PackageDescription and which component to build. It defaults to create the Paths_* module or else returns Nothing so others can be built with a different hook.

With this it would be possible to override the Paths_* module and generate modules on the fly without having to guess where to put them (dist/build, dist/build/exe, dist/libbuild, etc) or when to create them (on configure, on build, before cpp, etc).

[ezyang]

@fmaste, do you want to make a ticket describing this suggestion in more detail (like a spec), and then edit the description here to link to it?

[ezyang]

Sorry, I don't think this is going to happen for 2.0.