[ travis ] Reviving the travis builds

The current commit makes the travis builds operational once again.
It's simply pulling the latest master from agda/agda & compiling
it so it's slow and prone to failure if master doesn't compile.

To speed up the build, .cabal and .ghc are cached using a script
taken from hvr/multi-ghc-travis

.travis.yml

@@ -1,26 +1,60 @@
-language: haskell
+language: c
 branches:
   only:
   - master
 
+sudo: false
+
+dist: trusty
+
+cache:
+  directories:
+    - $HOME/.cabsnap
+
+matrix:
+  include:
+    - env: TEST=MAIN GHC_VER=8.0.2 BUILD=CABAL CABAL_VER=1.24
+      addons:
+        apt:
+          packages:
+            - alex-3.1.7
+            - cabal-install-1.24
+            - ghc-8.0.2
+            - happy-1.19.5
+          sources:
+            - hvr-ghc
+
 before_install:
-  # Decrypting the dropbox credentials 
-  - openssl aes-256-cbc -K $encrypted_3f6e0f4132ed_key -iv $encrypted_3f6e0f4132ed_iv -in .dropbox_uploader.enc -out .dropbox_uploader -d
-  - cp .dropbox_uploader $HOME/
+  - export PATH=/opt/ghc/$GHC_VER/bin:/opt/cabal/$CABAL_VER/bin:/opt/alex/3.1.7/bin:/opt/happy/1.19.5/bin:~/.cabal/bin/:$PATH;
 
 install:
-  # Installing the dropbox download script
-  - cd $HOME
-  - curl "https://raw.githubusercontent.com/andreafabrizi/Dropbox-Uploader/master/dropbox_uploader.sh" -o dropbox_uploader.sh
-  - chmod +x dropbox_uploader.sh
-  # downloading the last (latest?) tarball and installing agda
-  - AGDATAR=$(./dropbox_uploader.sh list | tail -n 1 | sed 's/^.*\(Agda.*\)$/\1/')
-  - ./dropbox_uploader.sh download $AGDATAR .
-  - tar -xzvf $AGDATAR
-  - cd $( basename $AGDATAR .tar.gz )
-  - sudo ./deploy.sh
+  - git clone https://github.com/agda/agda --depth=1 --single-branch
+  - cabal update
+  - sed -i 's/^jobs:/-- jobs:/' $HOME/.cabal/config
+  # checking whether .ghc is still valid
+  - cabal install --only-dependencies --dry -v > $HOME/installplan.txt
+  - sed -i -e '1,/^Resolving /d' $HOME/installplan.txt; cat $HOME/installplan.txt
+  - touch $HOME/.cabsnap/intallplan.txt
+  - mkdir -p $HOME/.cabsnap/ghc $HOME/.cabsnap/lib $HOME/.cabsnap/share $HOME/.cabsnap/bin
+  - if diff -u $HOME/.cabsnap/installplan.txt $HOME/installplan.txt;
+    then
+      echo "cabal build-cache HIT";
+      rm -rfv .ghc;
+      cp -a $HOME/.cabsnap/ghc $HOME/.ghc;
+      cp -a $HOME/.cabsnap/lib $HOME/.cabsnap/share $HOME/.cabsnap/bin $HOME/.cabal/;
+    else
+      echo "cabal build-cache MISS";
+      rm -rf $HOME/.cabsnap;
+      mkdir -p $HOME/.ghc $HOME/.cabal/lib $HOME/.cabal/share $HOME/.cabal/bin;
+    fi
+  - cabal install cpphs
+  - cd agda && cabal install --only-dependencies && make CABAL_OPTS=-v2 install-bin
+  # snapshot package-db on cache miss
+  - echo "snapshotting package-db to build-cache";
+    mkdir $HOME/.cabsnap;
+    cp -a $HOME/.ghc $HOME/.cabsnap/ghc;
+    cp -a $HOME/.cabal/lib $HOME/.cabal/share $HOME/.cabal/bin $HOME/installplan.txt $HOME/.cabsnap/;
   # generating Everything.agda
-  - cabal install filemanip
   - cd $HOME/build/agda/agda-stdlib
   - runghc GenerateEverything.hs
 
@@ -46,7 +80,3 @@ after_success:
 notifications:
   email: false
 
-# Github token
-env:
-  global:
-    secure: f0GRSKTlAw6FdrvkI8LjP5ZhwcGBltJ1t5+nxipqfoR3VczMxcNgXD7bdwtUojFYR48jMs2W+LxEoJcuSH4bsdCeoSfpZ0nU424MDajGh0wuhAbSYKQXPWjFOxwMgC23sCySKhDAZiqN/Wd6orwV1p5JhuJkSCHdVeyUp+hLvIw=