Caution: This program can cause arbitrary code to run on your machine.
For example, if any modules use TH, then the TH will be executed.
configure scripts will be run. Custom Setup.hs programs will be run.

Here's a run with the HEAD, no special options:

$ ht normal ../cabal-install/dist/build/cabal/cabal  \
            /home/ian/ghc/darcs/ghc/inst/bin/ghc     \
            /home/ian/ghc/darcs/ghc/inst/bin/ghc-pkg \
            "" ""
[7.75 hours pass]

Then another run, this time using -XAlternativeLayoutRule to compile
each package (but not the build dependencies of the package):

$ ht alternative ../cabal-install/dist/build/cabal/cabal  \
                 /home/ian/ghc/darcs/ghc/inst/bin/ghc     \
                 /home/ian/ghc/darcs/ghc/inst/bin/ghc-pkg \
                 ""                                       \
                 "--ghc-option=-XAlternativeLayoutRule"
[7 hours pass]

And finally a comparison of the results:

$ htc normal alternative
                            normal
                         Buildable Build failed Deps failed Not tried
alternative Buildable          628            0           0         0
            Build failed        73          215           0         0
            Deps failed          0            0         170         0
            Not tried            0            0           0         0

i.e. 73 packages became unbuildable when the alternative layout rule was
used.