implement local::lib caching

Author: mohawk2

README.md

@@ -116,8 +116,17 @@ There are various environment variables that will control how a build is done.
     generation process if it has heavy dependencies, such as Dist::Zilla, and
     testing is being done on a freshly built perl.
 
+    Makes a local::lib that is blank.
+
     Defaults to true.
 
+  * `LOCAL_LIB_CACHE`
+
+    The directory used to cache the local::lib used if you specify
+    `local-lib cache`.
+
+    Defaults to `$HOME/.perlbrew-cache`.
+
   * `CPAN_MIRROR`
 
     The CPAN mirror that dependencies will be installed from.
@@ -278,6 +287,52 @@ Commands
     or built if not, and added to the library path. This is taken care
     of by the `build-perl` step.
 
+    There is a special local::lib name you can give:
+    `cache`, which works together with [Travis's caching
+    feature](https://docs.travis-ci.com/user/caching). Its location
+    defaults to `$HOME/.perlbrew-cache` but can be overridden
+    by supplying the environment variable `LOCAL_LIB_CACHE`. Use it
+    like this:
+
+        cache:
+          directories:
+          - $HOME/.perlbrew-cache # keeps between builds here
+        perl:
+          - "5.8.4@moo"
+        before_install:
+          - git clone git://github.com/travis-perl/helpers ~/travis-perl-helpers
+          - source ~/travis-perl-helpers/init
+          - build-perl
+          - local-lib cache # makes a local::lib from cached
+          - perl -V
+          - build-dist
+          - cd $BUILD_DIR
+        install:
+          - cpan-install --deps # installs prereqs, including recommends
+        before_cache:
+          - local-lib-cachestore # saves for local::lib next time
+
+    Alternatively, this will also work and the `build-perl` will do the
+    `local-lib` step for you:
+
+        cache:
+          directories:
+          - $HOME/.perlbrew-cache # keeps between builds here
+        perl:
+          - "5.8.4@cache"
+        before_install:
+          - git clone git://github.com/travis-perl/helpers ~/travis-perl-helpers
+          - source ~/travis-perl-helpers/init
+          - build-perl
+        # no need for local-lib cache
+          - perl -V
+          - build-dist
+          - cd $BUILD_DIR
+        install:
+          - cpan-install --deps # installs prereqs, including recommends
+        before_cache:
+          - local-lib-cachestore # saves for local::lib next time
+
 local::lib
 ----------
 A number of [predefined local::lib](share/local-libs.txt) directories are

bin/local-lib

@@ -7,12 +7,17 @@ if [ -z "$1" ]; then
   ll_roots=("$(mktemp -d -t local-lib-XXXXXX)")
 else
   for lib; do
-    if [ -z "$LL_NO_INSTALL" ]; then
-      # redirect since output of this gets eval-ed
-      if $HELPERS_ROOT/bin/local-lib-installer "$lib" 1>&2; then
-        ll_roots+=("$PERLBREW_HOME/libs/$PERLBREW_PERL@$lib")
+    if [ "$lib" == "cache" ]; then
+      $HELPERS_ROOT/bin/local-lib-cache use
+    else
+      if [ -z "$LL_NO_INSTALL" ]; then
+        # redirect since output of this gets eval-ed
+        if $HELPERS_ROOT/bin/local-lib-installer "$lib" 1>&2; then
+          ll_roots+=("$PERLBREW_HOME/libs/$PERLBREW_PERL@$lib")
+        fi
       fi
     fi
+    ll_roots+=("$PERLBREW_HOME/libs/$PERLBREW_PERL@$lib")
   done
 fi
 

bin/local-lib-cache

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+# usage:
+#  $0 use
+#    copies from cache location to perlbrew location
+#  $0 store
+#    copies from perlbrew location to cache location
+
+# locations:
+cache_location="$LOCAL_LIB_CACHE"
+full_version="$PERLBREW_PERL@cache"
+perlbrew_location="$PERLBREW_HOME/libs/$full_version"
+
+[ -z "$HELPERS_ROOT" ] && export HELPERS_ROOT="$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )"
+source "$HELPERS_ROOT/lib/debug.sh"
+exec 1>&2 # since local-lib calls this, then evals stdout - any echo to stderr
+
+if [ -z "$PERLBREW_ROOT" ]; then
+  echo "Must be run under perlbrew!"
+  exit 1
+fi
+
+source "$PERLBREW_ROOT/etc/bashrc"
+
+set -e
+
+if [ "$1" == "use" ]; then
+  perlbrew lib create "$full_version"
+  perlbrew use "$full_version"
+  mkdir -p "$perlbrew_location"
+  cp -pr "$cache_location"/* "$perlbrew_location"
+elif [ "$1" == "store" ]; then
+  id
+  echo "BEFORE"; find "$perlbrew_location" "$cache_location" -ls
+  mkdir -p "$cache_location"
+  cp -pr "$perlbrew_location"/* "$cache_location"
+  echo "AFTER"; find "$cache_location" -ls
+else
+  echo "Unknown arg '$1'"
+  exit 1
+fi

init

@@ -19,6 +19,7 @@ export SYSTEM_CORES="$(grep -c ^processor /proc/cpuinfo 2>/dev/null || sysctl -n
 [ -z "$AUTHOR_TESTING"  ] && export AUTHOR_TESTING=1
 [ -z "$SPLIT_BUILD"     ] && export SPLIT_BUILD=1
 [ "$COVERAGE" == "1"    ] && export COVERAGE=coveralls # drop this eventually
+[ -z "$LOCAL_LIB_CACHE" ] && export LOCAL_LIB_CACHE="$HOME/.perlbrew-cache"
 [ -z "$PERL_AUTOINSTALL_PREFER_CPAN" ]  && export PERL_AUTOINSTALL_PREFER_CPAN=1
 [ -z "$PERL_MM_USE_DEFAULT" ]           && export PERL_MM_USE_DEFAULT=1
 [ -z "$NONINTERACTIVE_TESTING" ]        && export NONINTERACTIVE_TESTING=1
@@ -52,6 +53,10 @@ function local-lib {
   eval "$("$HELPERS_ROOT/bin/local-lib" "$@")"
 }
 
+function local-lib-cachestore {
+  $HELPERS_ROOT/bin/local-lib-cache store
+}
+
 function build-perl {
   local TRAVIS_PERL_VERSION="$TRAVIS_PERL_VERSION"
   if [[ ( "$TRAVIS_PERL_VERSION" =~ ^5\.6[.-] || \