[GHC] #8558: Build xhtml and haddock only when `HADDOCK_DOCS=YES`

[GHC]

#8558: Build xhtml and haddock only when `HADDOCK_DOCS=YES`
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       Reporter:  nomeata           |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Build System      |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 In order to save contributor’s time, and in order to run the test suite
 faster, I suggest to not builds haddock and its dependencies (xhtml,
 anything else?) if `HADDOCK_DOCS=YES` is specified.

 The change is rather simple:
 {{{
 diff --git a/ghc.mk b/ghc.mk
 index dd91a82..b0f93a0 100644
 --- a/ghc.mk
 +++ b/ghc.mk
 @@ -437,7 +437,9 @@ REGULAR_INSTALL_PACKAGES += compiler
  endif
  REGULAR_INSTALL_PACKAGES += $(addprefix libraries/,$(PACKAGES_STAGE2))

 +ifeq "$(HADDOCK_DOCS)" "YES"
  PACKAGES_STAGE1 += xhtml
 +endif
  ifeq "$(Windows_Target)" "NO"
  ifneq "$(TargetOS_CPP)" "ios"
  PACKAGES_STAGE1 += terminfo
 @@ -652,8 +654,10 @@ BUILD_DIRS += libraries/integer-gmp/gmp
  BUILD_DIRS += libraries/integer-gmp/mkGmpDerivedConstants
  endif

 +ifeq "$(HADDOCK_DOCS)" "YES"
  BUILD_DIRS += utils/haddock
  BUILD_DIRS += utils/haddock/doc
 +endif
  BUILD_DIRS += compiler
  BUILD_DIRS += utils/hsc2hs
  BUILD_DIRS += utils/ghc-pkg
 }}}
 and it does not affect validate runs, as validate has `HADDOCK_DOCS` set
 to `YES`.

 If this is introduced, I suggest to annotate these two with a tag in
 packages, so that one can run `./sync-all get --no-haddock`, similar to
 `--no-dph`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8558>
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