internal/ci: evict workflow caches on a daily basis

The GitHub actions caches in the main and trybot repos can get large. So
large in fact we got the following warning from GitHub:

"Approaching total cache storage limit (34.5 GB of 10 GB Used)"

Yes, you did read that right.

Not only does this have the effect of causing us to breach "limits" it
also means that we can't be sure that individual caches are not bloated.

Fix that by purging the actions caches on a daily basis at 0200,
followed 15 mins later by a re-run of the tip trybots to repopulate the
caches so they are warm and minimal.

In testing with @mvdan, this resulted in cache sizes for Linux dropping
from ~1GB to ~125MB. This is a considerable saving.

Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: Ia3817b92828892878787c0d1f6843d07633b8007
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/551250
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

.github/workflows/evict_caches.yml

@@ -0,0 +1,33 @@
+# Code generated internal/ci/ci_tool.cue; DO NOT EDIT.
+
+name: Evict caches
+"on":
+  push:
+    branches:
+      - ci/test
+  schedule:
+    - cron: 0 2 * * *
+jobs:
+  test:
+    if: ${{github.repository == 'cue-lang/cue'}}
+    runs-on: ubuntu-22.04
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - run: |-
+          set -eux
+
+          echo ${{ secrets.CUECKOO_GITHUB_PAT }} | gh auth login --with-token
+          gh extension install actions/gh-actions-cache
+          for i in https://github.com/cue-lang/cue https://github.com/cue-lang/cue-trybot
+          do
+          	echo "Evicting caches for $i"
+          	cd $(mktemp -d)
+          	git init
+          	git remote add origin $i
+          	for j in $(gh actions-cache list -L 100 | grep refs/ | awk '{print $1}')
+          	do
+          		gh actions-cache delete --confirm $j
+          	done
+          done

.github/workflows/trybot.yml

@@ -11,6 +11,8 @@ name: TryBot
     tags-ignore:
       - v*
   pull_request: {}
+  schedule:
+    - cron: 15 2 * * *
 jobs:
   test:
     strategy:

internal/ci/github/evict_caches.cue

@@ -0,0 +1,84 @@
+// Copyright 2023 The CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package github
+
+import (
+	"cuelang.org/go/internal/ci/core"
+
+	"github.com/SchemaStore/schemastore/src/schemas/json"
+)
+
+// The evict_caches removes "old" GitHub actions caches from the main repo and
+// the accompanying trybot repo. The job is only run in the main repo, because
+// that is the only place where the credentials exist.
+//
+// The GitHub actions caches in the main and trybot repos can get large. So
+// large in fact we got the following warning from GitHub:
+//
+//   "Approaching total cache storage limit (34.5 GB of 10 GB Used)"
+//
+// Yes, you did read that right.
+//
+// Not only does this have the effect of causing us to breach "limits" it also
+// means that we can't be sure that individual caches are not bloated.
+//
+// Fix that by purging the actions caches on a daily basis at 0200, followed 15
+// mins later by a re-run of the tip trybots to repopulate the caches so they
+// are warm and minimal.
+//
+// In testing with @mvdan, this resulted in cache sizes for Linux dropping from
+// ~1GB to ~125MB. This is a considerable saving.
+evict_caches: _base.#bashWorkflow & {
+	name: "Evict caches"
+
+	on: {
+		push: {
+			branches: [_base.#testDefaultBranch]
+		}
+		schedule: [
+			// We will run a schedule trybot build 15 minutes later to repopulate the caches
+			{cron: "0 2 * * *"},
+		]
+	}
+
+	jobs: {
+		test: {
+			// We only want to run this in the main repo
+			if:        "${{github.repository == '\(core.#githubRepositoryPath)'}}"
+			"runs-on": _#linuxMachine
+			steps: [
+				json.#step & {
+					run: """
+					set -eux
+
+					echo ${{ secrets.CUECKOO_GITHUB_PAT }} | gh auth login --with-token
+					gh extension install actions/gh-actions-cache
+					for i in \(core.#githubRepositoryURL) \(core.#githubRepositoryURL)-trybot
+					do
+						echo "Evicting caches for $i"
+						cd $(mktemp -d)
+						git init
+						git remote add origin $i
+						for j in $(gh actions-cache list -L 100 | grep refs/ | awk '{print $1}')
+						do
+							gh actions-cache delete --confirm $j
+						done
+					done
+					"""
+				},
+			]
+		}
+	}
+}

internal/ci/github/trybot.cue

@@ -39,6 +39,10 @@ trybot: _base.#bashWorkflow & {
 			"tags-ignore": [core.#releaseTagPattern]
 		}
 		pull_request: {}
+		schedule: [
+			// Run at 0215 each day, 15 mins after the cache eviction
+			{cron: "15 2 * * *"},
+		]
 	}
 
 	jobs: {

internal/ci/github/workflows.cue

@@ -53,6 +53,10 @@ workflows: [
 		file:   "push_tip_to_trybot.yml"
 		schema: push_tip_to_trybot
 	},
+	{
+		file:   "evict_caches.yml"
+		schema: evict_caches
+	},
 ]
 
 // _#protectedBranchPatterns is a list of glob patterns to match the protected