From 30851ae5fbe4afd5a44923fc55135c54db732011 Mon Sep 17 00:00:00 2001
From: patrick brisbin <pbrisbin@gmail.com>
Date: Mon, 22 Jan 2018 19:49:02 -0500
Subject: [PATCH] Replace checksum key with full source digest

Checksumming stack.yaml was a cargo-cult of interpreted languages, where
"build" artifacts are uniquely determined by the dependency lock file.

This approach would result in us refusing to store a new cache after
changing code (as long as it was the same resolver), and forever
recompiling any altered modules.

Computing a digest of all git-tracked files seems like the simplest way
to key compilation for now.
---
 .circleci/config.yml | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 0a498ec..a92a340 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -7,9 +7,13 @@ jobs:
       - image: fpco/stack-build:lts
     steps:
       - checkout
+      - run:
+          name: Source digest
+          command: git ls-files | xargs md5sum > digest
+
       - restore_cache:
           keys:
-            - stack-{{ .Branch }}-{{ checksum "stack.yaml" }}
+            - stack-{{ .Branch }}-{{ checksum "digest" }}
             - stack-{{ .Branch }}
             - stack-
       - run:
@@ -19,7 +23,7 @@ jobs:
           name: Build
           command: make build
       - save_cache:
-          key: stack-{{ .Branch }}-{{ checksum "stack.yaml" }}
+          key: stack-{{ .Branch }}-{{ checksum "digest" }}
           paths:
             - ~/.stack
             - ./.stack-work