For a slimmer GHC

[Ludovic Courtès]

Hello!

GHC is insanely large, 1.2G for its closure, most of which is itself:

--8<---------------cut here---------------start------------->8---
store item                                                       total    self
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2            1209.7   
860.5  71.1%
/gnu/store/k6r37137lfpg3l3igi50c7lj2za7kqly-ld-wrapper-0           153.7     
0.0   0.0%
/gnu/store/czs63sm4l0s4a56ab38dqvkx19yzylbq-perl-5.16.1            141.2    
49.2   4.1%
/gnu/store/hddjjpkfvwaf1j1q3qwpvby0rid3k8by-gcc-4.9.3              138.1    
77.3   6.4%
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc         120.2    
42.6   3.5%
/gnu/store/fmxxkrpwajcnb9cyncgh4f4z6ybknl1g-guile-2.0.11           109.0    
16.1   1.3%
/gnu/store/y5psndwpbbkjrf856x757psb708y62dn-binutils-2.25.1         82.5    
44.6   3.7%
/gnu/store/mnwjrkbfzkb5ifhqf8hssf3cxfvg11l6-coreutils-8.24          77.8    
13.8   1.1%
/gnu/store/fzp98iyq7a2i4d4siw0ab0y0wa95vv8k-readline-6.3            68.6     
1.2   0.1%

[...]

$ du -ms /gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/
871     /gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/
$ du -ms /gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/
871     /gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/
--8<---------------cut here---------------end--------------->8---

The main problem is that, for each module, we have three variants:

--8<---------------cut here---------------start------------->8---
$ du -ms    
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/*
3       
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/Control
1       
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/Data
5       
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/libHStransformers-0.4.2.0-3eG64VdP2vzGjP6wJiCp5X.a
2       
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/libHStransformers-0.4.2.0-3eG64VdP2vzGjP6wJiCp5X-ghc7.10.2.so
7       
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/trans_3eG64VdP2vzGjP6wJiCp5X/libHStransformers-0.4.2.0-3eG64VdP2vzGjP6wJiCp5X_p.a
--8<---------------cut here---------------end--------------->8---

What about removing all the .a?  Would that be OK?

On that topic I found
<https://ghc.haskell.org/trac/ghc/wiki/DynamicByDefault> but it’s not
clear to me whether this is relevant here.  At worst we can add a phase
that removes these files.

A secondary issue is documentation: There’s a “doc” output, but
‘ghc:out’ depends on ‘ghc:doc’:

--8<---------------cut here---------------start------------->8---
$ guix gc --references /gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/ 
| grep doc
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc
$ du -ms /gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc
47      /gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc
$ grep -r r539jrq7jk9vkmm1255i5jqs7skn4fag    
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/package.conf.d/process-1.2.3.0-f0287ac288afc0705be775d1adda59ee.conf:haddock-interfaces:
 
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc/share/doc/ghc/html/libraries/process-1.2.3.0/process.haddock
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/package.conf.d/process-1.2.3.0-f0287ac288afc0705be775d1adda59ee.conf:haddock-html:
 
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc/share/doc/ghc/html/libraries/process-1.2.3.0
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/package.conf.d/Cabal-1.22.4.0-43c3ae30d75ac742e521d26b63721876.conf:haddock-interfaces:
 
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc/share/doc/ghc/html/libraries/Cabal-1.22.4.0/Cabal.haddock
/gnu/store/1iwl222h2qw80fyr578sdjdki0pbcjm0-ghc-7.10.2/lib/ghc-7.10.2/package.conf.d/Cabal-1.22.4.0-43c3ae30d75ac742e521d26b63721876.conf:haddock-html:
 
/gnu/store/r539jrq7jk9vkmm1255i5jqs7skn4fag-ghc-7.10.2-doc/share/doc/ghc/html/libraries/Cabal-1.22.4.0
--8<---------------cut here---------------end--------------->8---

Any idea if we could avoid references to the “doc” output in these
*.conf files?  For instance, if there’s a variable like, say,
‘HADDOCK_PATH’, we can certainly remove the hardcoded references

Federico, Paul, Eric, … thoughts?  :-)

Thanks,
Ludo’.