Make sure Travis-CI actually tests older versions of GHC+containers

Currently it brings in the newest version of containers all the time,
which doesn't occur if anything actually depends upon fgl, causing
real world breakage like in #69.

Author: ivan-m

.travis.yml

@@ -11,13 +11,16 @@ before_cache:
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/build-reports.log
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.tar
 
+env:
+  global:
+    - CONF=""
+
 matrix:
-  fast_finish: true
   include:
-    - env: CABALVER=1.16 GHCVER=7.0.4
+    - env: CABALVER=1.16 GHCVER=7.0.4 CONF="-f -containers042"
       compiler: ": #GHC 7.0.4"
       addons: {apt: {packages: [cabal-install-1.16,ghc-7.0.4], sources: [hvr-ghc]}}
-    - env: CABALVER=1.16 GHCVER=7.2.2
+    - env: CABALVER=1.16 GHCVER=7.2.2 CONF="-f -containers042"
       compiler: ": #GHC 7.2.2"
       addons: {apt: {packages: [cabal-install-1.16,ghc-7.2.2], sources: [hvr-ghc]}}
     - env: CABALVER=1.16 GHCVER=7.4.2
@@ -56,11 +59,11 @@ install:
    fi
  - travis_retry cabal update -v
  - sed -i 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config
- - cabal install --only-dependencies --enable-tests --enable-benchmarks --dry -v > installplan.txt
+ - cabal install --only-dependencies --enable-tests --enable-benchmarks $CONF --dry -v > installplan.txt
  - sed -i -e '1,/^Resolving /d' installplan.txt; cat installplan.txt
 
 # check whether current requested install-plan matches cached package-db snapshot
- - if diff -u installplan.txt $HOME/.cabsnap/installplan.txt;
+ - if diff -u $HOME/.cabsnap/installplan.txt installplan.txt;
    then
      echo "cabal build-cache HIT";
      rm -rfv .ghc;
@@ -86,7 +89,7 @@ install:
 # any command which exits with a non-zero exit code causes the build to fail.
 script:
  - if [ -f configure.ac ]; then autoreconf -i; fi
- - cabal configure --enable-tests --enable-benchmarks -v2  # -v2 provides useful information for debugging
+ - cabal configure --enable-tests --enable-benchmarks -v2 $CONF # -v2 provides useful information for debugging
  - cabal build   # this builds all libraries and executables (including tests/benchmarks)
  - cabal test
  - cabal check
@@ -96,7 +99,7 @@ script:
 # If there are no other `.tar.gz` files in `dist`, this can be even simpler:
 # `cabal install --force-reinstalls dist/*-*.tar.gz`
  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
-   (cd dist && cabal install --force-reinstalls "$SRC_TGZ")
+   (cd dist && cabal install --force-reinstalls $CONF "$SRC_TGZ")
 
 # Check the fgl-arbitrary sub-package
  - cd fgl-arbitrary
@@ -110,5 +113,4 @@ script:
  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
    (cd dist && cabal install --force-reinstalls "$SRC_TGZ")
 
-
 # EOF