From 107ede6e0a37f7737fd14fb9e7ca228108ac34c1 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 15 Jul 2022 10:40:08 -0700
Subject: [PATCH] Add an output intended for cache keys

---
 .github/workflows/ci.yml |  1 +
 action.yml               | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1bc54a1d..f937a308 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -32,4 +32,5 @@ jobs:
           toolchain: ${{matrix.rust}}
       - name: Check ${{'${{steps.toolchain.outputs.version}}'}}
         run: echo '${{steps.toolchain.outputs.version}}'
+        run: echo '${{steps.toolchain.outputs.cachekey}}'
       - run: rustc --version
diff --git a/action.yml b/action.yml
index 22735888..70ed65fb 100644
--- a/action.yml
+++ b/action.yml
@@ -17,8 +17,11 @@ inputs:
     required: false
 
 outputs:
+  cachekey:
+    description: A short hash of the rustc version, appropriate for use as a cache key. "20220627b61e"
+    value: ${{steps.rustc-version.outputs.cachekey}}
   version:
-    description: Version as reported by `rustc --version`, e.g. "rustc 1.62.0 (a8314ef7d 2022-06-27)"
+    description: Version as reported by `rustc --version`. "rustc 1.62.0 (a8314ef7d 2022-06-27)"
     value: ${{steps.rustc-version.outputs.version}}
 
 runs:
@@ -48,7 +51,12 @@ runs:
     - run: rustup default ${{inputs.toolchain}}
       shell: bash
     - id: rustc-version
-      run: echo "::set-output name=version::$(rustc --version)"
+      run: |
+        : set outputs
+        DATE=$(rustc --version --verbose | sed -ne 's/^commit-date: \(20[0-9][0-9]\)-\([01][0-9]\)-\([0-3][0-9]\)$/\1\2\3/p')
+        HASH=$(rustc --version | sha256sum)
+        echo "::set-output name=cachekey::$(echo $DATE$HASH | head -c12)"
+        echo "::set-output name=version::$(rustc --version)"
       shell: bash
     - run: rustc --version --verbose
       shell: bash