From 095f287f155c0e38e46631d45e397a1e9d705dec Mon Sep 17 00:00:00 2001
From: Mikhail Glushenkov <mikhail.glushenkov@gmail.com>
Date: Fri, 9 Jun 2017 15:34:47 +0200
Subject: [PATCH] Experiment with Travis's build stages.

See #4556.
---
 .travis.yml        | 31 ++++++++++++++++++++++++-------
 travis-precache.sh | 23 +++++++++++++++++++++++
 2 files changed, 47 insertions(+), 7 deletions(-)
 create mode 100755 travis-precache.sh

diff --git a/.travis.yml b/.travis.yml
index 1b77cec836e..a9410adb3f3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -114,13 +114,30 @@ install:
  # We intentionally do not install anything before trying to build Cabal because
  # it should build with each supported GHC version out-of-the-box.
 
-# Here starts the actual work to be performed for the package under test; any
-# command which exits with a non-zero exit code causes the build to fail. Using
-# ./dist/setup/setup here instead of cabal-install to avoid breakage when the
-# build config format changed.
-script:
- - rm -rf dist-newstyle
- - ./travis-${SCRIPT}.sh -j2
+# All jobs except 'meta' have two stages; the first stage is used to
+# warm up the cache. This is mostly useful when a new compiler gets
+# added to the build matrix: work done installing dependencies is not
+# wasted when we exceed the time limit for jobs.
+jobs:
+  include:
+    - stage: prepare cache
+      env:
+        # All except 'meta' basically.
+        - SCRIPT=script
+        - SCRIPT=solver-debug-flags
+        - SCRIPT=bootstrap
+        - SCRIPT=stack
+      script: ./travis-precache.sh
+      after_success: skip
+    - stage: test
+      # Here starts the actual work to be performed for the package
+      # under test; any command which exits with a non-zero exit code
+      # causes the build to fail. Using ./dist/setup/setup here
+      # instead of cabal-install to avoid breakage when the build
+      # config format changed.
+      script:
+        - rm -rf dist-newstyle
+        - ./travis-${SCRIPT}.sh -j2
 
 cache:
  directories:
diff --git a/travis-precache.sh b/travis-precache.sh
new file mode 100755
index 00000000000..63fe53b3ab3
--- /dev/null
+++ b/travis-precache.sh
@@ -0,0 +1,23 @@
+#!/bin/sh
+
+. ./travis-common.sh
+
+# ---------------------------------------------------------------------
+# Update the Cabal index
+# ---------------------------------------------------------------------
+
+timed cabal update
+
+# ---------------------------------------------------------------------
+# Setup our local project
+# ---------------------------------------------------------------------
+
+cp cabal.project.travis cabal.project.local
+
+# ---------------------------------------------------------------------
+# Warm up the cache
+# ---------------------------------------------------------------------
+
+# TODO: Don't build Cabal and hackage-security here, they'll be
+# rebuilt anyway.
+timed cabal new-build --only-dependencies cabal-install cabal-tests