HexChat.log

Jul 27 21:04:52 <fendor>	Hi! I have a question regarding per-component builds. In the context of my gsoc, I am trying to extend Cabal/cabal-install to open a repl session for multiple components at once, e.g. it should support `caal repl <lib> <exe>`. My first step was to allow in Cabal `runghc Setup.hs repl <lib> <exe>` which works if the project is configured via `cabal configure`, which seems to be the old way of doing stuff. As far as I can tell, cabal 
Jul 27 21:04:52 <fendor>	uses per-component builds, e.g. it configures a component, then builds it immediately. The problem now is that I can not call Cabal directly via `runghc Setup.hs repl <lib> <exe>` because the library component is not configured.  
Jul 27 21:05:46 <fendor>	It is not configured, since <exe> got configured after building the lib, which causes lib to be un-configured, afaict.
Jul 27 21:07:48 <fendor>	My first question is, are these findings correct? If yes, the follow-up question is how can we change Cabal or cabal, to either allow to configure multiple components at once, so that `runghc Setup.hs repl <lib> <exe>` works
Jul 27 21:08:07 <fendor>	or maybe the solution can be in cabal-install land altogether
Jul 27 21:15:53 <phadej>	- you cannot configure `exe` if `lib` is not built, if exe depends on lib. Configuring exe will check that lib is built, and otherwise say "cannot satisfy dependencies" or something like that.
Jul 27 21:16:50 <phadej>	- Don't complicate ./Setup interface, IMO it's fine to exclude `build-type: Custom` etc "special treatment" required packages from this functionality
Jul 27 21:17:12 <phadej>	- then `cabal-install` can do whatever needed
Jul 27 21:19:17 <fendor>	but after configuring exe successfully, I can not open a repl session for the lib, right?
Jul 27 21:19:36 <fendor>	phadej, would it be ok for cabal-install to call ghc directly? 
Jul 27 21:20:22 <fendor>	also, how can cabal-install obtain the required options from Cabal? Or could I avoid Cabal altogether?
Jul 27 21:27:23 <phadej>	you don't need to configure, you need to run preprocessors and maybe do other stuff
Jul 27 21:27:30 <phadej>	which is infact part of "build" phase
Jul 27 21:28:09 <phadej>	and `cabal-install` can call GHC directly, through Cabal library. Which is different then through `./Setup` cli interface.
Jul 27 21:29:28 <phadej>	key point: you do need to some preparations steps, but those aren't "./Setup configure", as it does stuff you don't need, and also does stuff you don't need.
Jul 27 21:29:35 <phadej>	doesn't do stuff you need*
Jul 27 21:30:50 <fendor>	Should these preparations steps be done in Cabal, e.g. factor out a new command, or can they be performed by cabal-install?
Jul 27 21:32:17 <phadej>	I'm 100% against teaching ./Setup anything not-related to "building packages"
Jul 27 21:32:28 <phadej>	if it doesn't need to be there, it shouldn't.
Jul 27 21:32:39 <fendor>	that is fine by me, I am just asking for a possible implementation plan
Jul 27 21:32:52 <fendor>	I am not insisting on changing anything in Cabal
Jul 27 21:33:13 <phadej>	it would be also easier to not touch anything in Cabal external cli interface
Jul 27 21:33:28 *	fendor_ has quit (Ping timeout: 246 seconds)
Jul 27 21:33:29 <phadej>	otherwise you will run out of time figuring out all the corner cases
Jul 27 21:33:45 <phadej>	so it's both cleaner, and faster.
Jul 27 21:33:48 <phadej>	win-wn
Jul 27 21:34:53 <phadej>	(AND IMO, excluding `build-type: Custom` packages - which require interaction via `./Setup` is fine, otherwise you'll also need to specify what hooks are run and when)
Jul 27 21:34:58 <fendor>	ok, nice. So, I just heard the nix-infrastructure might be all I need. Does that sound reasonable?
Jul 27 21:35:12 <phadej>	nix-infrastructure?
Jul 27 21:36:10 <fendor>	nix-build infrastructure
Jul 27 21:36:27 <fendor>	but I may have misunderstood.
Jul 27 21:38:26 <fendor>	so, I should not use Cabal's repl to open the multi component repl session?
Jul 27 21:40:08 <fendor>	but rather call ghc via the Cabal lib interface
Jul 27 21:41:37 <phadej>	no. Teaching `./Cabal` about multi-component repl session would mean teaching Cabal about multi-component builds
Jul 27 21:42:03 <phadej>	which is, I'm not exaggerrating, would require very big rewrite - as it is very single-component centered
Jul 27 21:43:18 <fendor>	it seems, all that needs to be done is to have code path that runs the relevant preprocessors (which can be essentially a build for now), then obtain relevant compilation options and call ghc directly, right?
Jul 27 21:45:15 <phadej>	yes, for your needs just doing a build is probably fine - except when it fails
Jul 27 21:45:25 <phadej>	but good start
Jul 27 21:45:53 <fendor>	ok, sounds nice, thank you! last question, do you know how I obtain the compilation options per component?
Jul 27 21:51:09 <phadej>	you have to look up how componentlocalbuildinfo is conjured and where
Jul 27 21:51:18 <fendor>	thanks! 
Jul 27 21:51:23 <phadej>	and how you can execute the same codepaths
Jul 27 21:51:29 <phadej>	(as it's probably constructed during configure)
Jul 27 21:51:41 <phadej>	though, if you `build` you `./Setup configure`...
Jul 27 21:58:56 <fendor>	that sounds doable, thank you for the help!