From c3d496b49fc8eec1daed00d5411bd51c78e2ce4a Mon Sep 17 00:00:00 2001
From: Mike <mike@sillyhouse.net>
Date: Wed, 17 Jul 2024 12:34:13 +0100
Subject: [PATCH] Update CI ccache on every push to develop (#2865)

Build times are increasing faster than I expected, so it's clear that to be effective the ccache needs to be kept up to date.
This needs to happen automatically so we can forget about it.

Github caching behaviour is to fail the save operation if a hit occurred on primary key.
In other words, a cache entry will never be overwritten (updated).
There is no provision for a cache update as such: https://github.com/actions/cache/issues/342

The workaround is fairly easy though: break into discrete restore/delete/save steps.

Only the cache for the current branch is deleted, using the `--branch` option to `gh action-cache delete`.
This prevents pull requests from contributors with repo write access from deleting the main `develop` cache.

This table shows the intended progression of cache updates, starting from an empty cache:

| Event   | Branch       | Restore      | Delete  | Save         |
| ------- | ------------ | --------     | ------- | ------------ |
| PR      | feature/new  | -            | -       | feature/new  |
| PR      | feature/new  | feature/new  | -       | -            |
| Merge   | develop      | -            | -       | develop      |
| PR      | fix/lwip     | develop      | -       | -            |
| Merge   | develop      | develop      | develop | develop      |

So always save if (event.branch == develop) or no cache hit
---
 .github/workflows/ci-esp32.yml | 21 +++++++++++++++++++--
 .github/workflows/ci.yml       | 21 +++++++++++++++++++--
 .github/workflows/library.yml  | 21 +++++++++++++++++++--
 3 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/.github/workflows/ci-esp32.yml b/.github/workflows/ci-esp32.yml
index 4b12890873..6b37b2aeff 100644
--- a/.github/workflows/ci-esp32.yml
+++ b/.github/workflows/ci-esp32.yml
@@ -86,8 +86,9 @@ jobs:
         . Tools/ci/setenv.ps1
         Tools/ci/install.cmd
 
-    - name: Compiler Cache
-      uses: actions/cache@v4
+    - name: Restore Compiler Cache
+      id: ccache
+      uses: actions/cache/restore@v4
       with:
         path: .ccache
         key: ${{ matrix.os }}-ccache-${{ matrix.variant }}-${{ matrix.idf_version }}
@@ -106,3 +107,19 @@ jobs:
 
     - name: Compiler Cache stats
       run: ccache -sv
+
+    - name: Delete Previous Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch && steps.ccache.outputs.cache-hit
+      continue-on-error: true
+      run: |
+        gh extension install actions/gh-actions-cache
+        gh actions-cache delete "${{ steps.ccache.outputs.cache-primary-key }}" --branch ${{ github.ref_name }} --confirm
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Save Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch || !steps.ccache.outputs.cache-hit
+      uses: actions/cache/save@v4
+      with:
+        path: .ccache
+        key: ${{ steps.ccache.outputs.cache-primary-key }}
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8a639444de..536ab4e988 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -75,8 +75,9 @@ jobs:
         . Tools/ci/setenv.ps1
         Tools/ci/install.cmd
 
-    - name: Compiler Cache
-      uses: actions/cache@v4
+    - name: Restore Compiler Cache
+      id: ccache
+      uses: actions/cache/restore@v4
       with:
         path: .ccache
         key: ${{ matrix.os }}-ccache-${{ matrix.toolchain }}-${{ matrix.variant }}
@@ -97,3 +98,19 @@ jobs:
 
     - name: Compiler Cache stats
       run: ccache -sv
+
+    - name: Delete Previous Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch && steps.ccache.outputs.cache-hit
+      continue-on-error: true
+      run: |
+        gh extension install actions/gh-actions-cache
+        gh actions-cache delete "${{ steps.ccache.outputs.cache-primary-key }}" --branch ${{ github.ref_name }} --confirm
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Save Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch || !steps.ccache.outputs.cache-hit
+      uses: actions/cache/save@v4
+      with:
+        path: .ccache
+        key: ${{ steps.ccache.outputs.cache-primary-key }}
diff --git a/.github/workflows/library.yml b/.github/workflows/library.yml
index 126d3699ed..b01b4dbdd8 100644
--- a/.github/workflows/library.yml
+++ b/.github/workflows/library.yml
@@ -133,8 +133,9 @@ jobs:
         . Tools/ci/setenv.ps1
         Tools/ci/install.cmd
 
-    - name: Compiler Cache
-      uses: actions/cache@v4
+    - name: Restore Compiler Cache
+      id: ccache
+      uses: actions/cache/restore@v4
       with:
         path: .ccache
         key: ${{ matrix.os }}-ccache-${{ matrix.variant }}-${{ matrix.arch == 'Esp32' && env.INSTALL_IDF_VER || '' }}
@@ -155,3 +156,19 @@ jobs:
 
     - name: Compiler Cache stats
       run: ccache -sv
+
+    - name: Delete Previous Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch && steps.ccache.outputs.cache-hit
+      continue-on-error: true
+      run: |
+        gh extension install actions/gh-actions-cache
+        gh actions-cache delete "${{ steps.ccache.outputs.cache-primary-key }}" --branch ${{ github.ref_name }} --confirm
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Save Compiler Cache
+      if: github.ref_name == github.event.repository.default_branch || !steps.ccache.outputs.cache-hit
+      uses: actions/cache/save@v4
+      with:
+        path: .ccache
+        key: ${{ steps.ccache.outputs.cache-primary-key }}