cache ccache

.travis.yml

@@ -33,6 +33,8 @@ cache:
     - /usr/local/Homebrew/
     # used in OSX custom build script dealing with local bottle caching
     - $HOME/local_bottle_metadata
+    # `cache: ccache: true` has no effect if `language:` is not `c` or `cpp`
+    - $HOME/.ccache
     
 matrix:
   fast_finish: true

config.sh

@@ -56,6 +56,12 @@ function pre_build {
     # see https://docs.brew.sh/Manpage , "info formula" section
     export HOMEBREW_NO_GITHUB_API=1
 
+    # https://docs.travis-ci.com/user/caching/#ccache-cache
+    # No need to allow rc 1 -- if this triggers a timeout,
+    #  something is clearly wrong
+    brew_install_and_cache_within_time_limit ccache
+    export PATH="/usr/local/opt/ccache/libexec:$PATH"
+
     echo 'Installing QT4'
     brew tap | grep -qxF cartr/qt4 || brew tap -v cartr/qt4
     brew tap --list-pinned | grep -qxF cartr/qt4 || brew tap-pin -v cartr/qt4