Auto merge of #897 - emilio:ci-cache, r=fitzgen

ci: Cache LLVM builds.

Fixes #896

Author: bors-servo

.travis.yml

@@ -30,6 +30,7 @@ matrix:
 cache:
   directories:
     - $HOME/.cargo
+    - $HOME/.llvm-builds
 
 before_install: . ./ci/before_install.sh
 

ci/before_install.sh

@@ -6,25 +6,31 @@ if [ "${TRAVIS_OS_NAME}" == "osx" ]; then
     rvm get head || true
 fi
 
-function llvm_download() {
+function llvm_download_if_needed() {
     export LLVM_VERSION_TRIPLE="${LLVM_VERSION}"
     export LLVM=clang+llvm-${LLVM_VERSION_TRIPLE}-x86_64-$1
 
-    wget http://llvm.org/releases/${LLVM_VERSION_TRIPLE}/${LLVM}.tar.xz
-    mkdir llvm
-    tar -xf ${LLVM}.tar.xz -C llvm --strip-components=1
+    local llvm_build_dir="$HOME/.llvm-builds/${LLVM}"
 
-    export LLVM_CONFIG_PATH=`pwd`/llvm/bin/llvm-config
+    if [ -d "${llvm_build_dir}" ]; then
+        echo "Using cached LLVM build for ${LLVM} in ${llvm_build_dir}";
+    else
+        wget http://llvm.org/releases/${LLVM_VERSION_TRIPLE}/${LLVM}.tar.xz
+        mkdir -p "${llvm_build_dir}"
+        tar -xf ${LLVM}.tar.xz -C "${llvm_build_dir}" --strip-components=1
+    fi
+
+    export LLVM_CONFIG_PATH="${llvm_build_dir}/bin/llvm-config"
     if [ "${TRAVIS_OS_NAME}" == "osx" ]; then
-        cp llvm/lib/libclang.dylib /usr/local/lib/libclang.dylib
+        cp "${llvm_build_dir}/lib/libclang.dylib" /usr/local/lib/libclang.dylib
     fi
 }
 
 
 if [ "${TRAVIS_OS_NAME}" == "linux" ]; then
-    llvm_download linux-gnu-ubuntu-14.04
+    llvm_download_if_needed linux-gnu-ubuntu-14.04
 else
-    llvm_download apple-darwin
+    llvm_download_if_needed apple-darwin
 fi
 
 popd