[commit: ghc] master: Cabal-level sanity check to enforce Cabal flag-invariant (0e21678)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/0e21678677894ed7cb236499ec6f2041efae22a2/ghc

>---------------------------------------------------------------

commit 0e21678677894ed7cb236499ec6f2041efae22a2
Author: Herbert Valerio Riedel <hvr at gnu.org>
Date:   Tue Nov 3 16:18:30 2015 -0600

    Cabal-level sanity check to enforce Cabal flag-invariant
    
    This helps catch cabal-flag misconfiguration early on during `cabal
    configure`, rather than much later in the build-process during
    compilation.
    
    Reviewed By: austin
    
    Differential Revision: https://phabricator.haskell.org/D1423


>---------------------------------------------------------------

0e21678677894ed7cb236499ec6f2041efae22a2
 libraries/base/base.cabal | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libraries/base/base.cabal b/libraries/base/base.cabal
index d98e7bf..e94d389 100644
--- a/libraries/base/base.cabal
+++ b/libraries/base/base.cabal
@@ -94,6 +94,11 @@ Library
         Unsafe
 
     build-depends: rts == 1.0.*, ghc-prim == 0.5.*
+
+    -- sanity-check to ensure exactly one flag is set
+    if !((flag(integer-gmp) && !flag(integer-simple)) || (!flag(integer-gmp) && flag(integer-simple)))
+        build-depends: invalid-cabal-flag-settings<0
+
     if flag(integer-simple)
         build-depends: integer-simple >= 0.1.1 && < 0.2