[GHC] #3345: Support reading .a files in GHCi to reclaim some disk space

[GHC]

#3345: Support reading .a files in GHCi to reclaim some disk space
-----------------------------+----------------------------------------------
Reporter:  batterseapower    |          Owner:                  
    Type:  feature request   |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  6.10.2            |       Severity:  normal          
Keywords:                    |       Testcase:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
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 Currently, Cabal builds two code files for every libary it installs:

 {{{
 mbolingbroke at mb566 ~/.cabal/lib/vector-space-0.5.6/ghc-6.10.1
 $ ls
 .
 ..
 Data
 HSvector-space-0.5.6.o
 libHSvector-space-0.5.6.a
 }}}

 The .a is a straight concatenation of the .o files that got built. The .o
 is the result of lding together all the .o files (and so has inter-object
 references already resolved) but is actually only used by GHCi.

 If GHCi could support loading .a files then Cabal wouldn't have to build
 this extra .o file and we could cut the size of installed libraries almost
 in half.

 (Or perhaps GHC could link against the .o rather than the .a, and then
 Cabal could stop building the .a, instead?)

 {{{
 [12:32] BSP_: does cabal build both .o and .a's for a library purely
 because ghci isn't capable of reading the .a format and loading each .o
 individually?
 [12:33] BSP_: it seems a bit wasteful to have two copies of the code
 installed for each library...
 [12:35] dcoutts: BSP_: that's correct
 [12:35] dcoutts: in theory it's not that hard
 [12:35] dcoutts: there's no real need for ghci to read the .a index, just
 link in everything
 [12:36] arjanb left the chat room. ("bbl")
 [12:36] dcoutts: the .a format is trivial
 [12:36] • dcoutts has a parser
 [12:36] dcoutts: and generator for that matter
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3345>
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