Rework pacman pkg cache and enable by default

Three main improvements:

* Create a separate cache for each input configuration: Assuming a build matrix
  which builds for different arches and has different dependencies we create
  a cache for each of them, while loading any of them.
* Prune caches before saving them: Every time a package has a new version we
  create a new cache which only includes the new packages. This makes sure that
  the cache/restore size stays as small as possible over time.
* Avoid cache race conditions: If a run doesn't change the cache we wont save it
  and if saving fails because another job created it in the mean time,
  we catch the error and ignore it.

Overall this cache doesn't save much time, since installation and initial setup
take the most time, but this should save a lot of traffic for our main
repo server.

And also this removes the cache option which was confusing some users because it
only caches packages and not everything.

README.md

@@ -146,24 +146,6 @@ Installing additional packages after updating the system is supported through op
       install: 'git base-devel'
 ```
 
-#### cache
-
-If set to `true`, directory `/var/cache/pacman/pkg` is restored/cached in order to speed up future updates:
-
-```yaml
-  - uses: msys2/setup-msys2@v1
-    with:
-      cache: true
-```
-
-If set to `save`, the same directory is cached, but it is not restored. This can be used to force a save of a clean state.
-
-```yaml
-  - uses: msys2/setup-msys2@v1
-    with:
-      cache: save
-```
-
 ## Development
 
 The steps to publish a new release are the following:

action.yml

@@ -24,10 +24,6 @@ inputs:
     description: 'Install packages after installation through pacman'
     required: false
     default: false
-  cache:
-    description: 'Cache /var/cache/pacman/pkg to speed up future updates'
-    required: false
-    default: false
 runs:
   using: 'node12'
   main: 'index.js'

main.js

@@ -5,6 +5,7 @@ const exec = require('@actions/exec');
 const tc = require('@actions/tool-cache');
 const path = require('path');
 const fs = require('fs');
+const crypto = require('crypto');
 const { hashElement } = require('folder-hash');
 
 const inst_url = 'https://github.com/msys2/msys2-installer/releases/download/2020-06-29/msys2-base-x86_64-20200629.sfx.exe';
@@ -36,7 +37,6 @@ async function run() {
     const p_pathtype = core.getInput('path-type');
     const p_msystem = core.getInput('msystem');
     const p_install = core.getInput('install');
-    const p_cache = core.getInput('cache');
 
     let base = 'C:';
 
@@ -75,15 +75,22 @@ async function run() {
     fs.writeFileSync(cmd, wrap);
 
     core.addPath(dest);
-    const c_paths = [(p_release ? dest : 'C:') + `\\msys64\\var\\cache\\pacman\\pkg\\`];
+    const pkgCachePath = (p_release ? dest : 'C:') + `\\msys64\\var\\cache\\pacman\\pkg\\`;
 
     core.exportVariable('MSYSTEM', p_msystem);
 
-    if (p_cache === 'true') {
-      core.startGroup('Restoring cache...');
-      console.log('Cache ID:', await cache.restoreCache(c_paths, 'msys2', ['msys2-']));
-      core.endGroup();
-    }
+    // We want a cache key that is ideally always the same for the same kind of job.
+    // So that mingw32 and ming64 jobs, and jobs with different install packages have different caches.
+    let shasum = crypto.createHash('sha1');
+    ['release', 'update', 'path-type', 'msystem', 'install'].map((n) => { return shasum.update(core.getInput(n)); });
+    const baseCacheKey = 'msys2-pkgs';
+    const jobCacheKey = baseCacheKey + '-conf:' + shasum.digest('hex').slice(0, 8);
+
+    core.startGroup('Restoring cache...');
+    // We ideally want a cache matching our configuration, but every cache is OK since we prune it later anyway
+    const restoreKey = await cache.restoreCache([pkgCachePath], jobCacheKey, [jobCacheKey, baseCacheKey]);
+    console.log(`Cache restore for ${jobCacheKey}, got ${restoreKey}`);
+    core.endGroup();
 
     async function run(args, opts) {
       await exec.exec('cmd', ['/D', '/S', '/C', cmd].concat(['-c', args.join(' ')]), opts);
@@ -116,12 +123,28 @@ async function run() {
       core.endGroup();
     }
 
-    if (p_cache === 'true' || p_cache === 'save') {
-      core.startGroup('Saving cache...');
-      const key = (await hashElement(c_paths[0]))['hash'].toString() + (new Date()).getTime().toString();
-      console.log('Cache ID:', await cache.saveCache(c_paths, 'msys2-' + key), '[' + key + ']');
-      core.endGroup();
+    core.startGroup('Prune cache...');
+    // Remove all uninstalled packages
+    await run(['paccache', '-r', '-f', '-u', '-k0']);
+    // Keep the newest for all other packages
+    await run(['paccache', '-r', '-f', '-k1']);
+    core.endGroup();
+
+    core.startGroup('Saving cache...');
+    const saveKey = jobCacheKey + '-files:' + (await hashElement(pkgCachePath))['hash'].toString();
+    if (restoreKey === saveKey) {
+      console.log(`Cache unchanged, skipping save for ${saveKey}`);
+    } else {
+      try {
+        const cacheId  = await cache.saveCache([pkgCachePath], saveKey);
+        console.log(`Cache saved as ID ${cacheId} using key ${saveKey}`);
+      } catch (error) {
+        // In case something created the same cache since we restored we'll get an error here,
+        // but that's OK with us, so ignore.
+        console.log(error.message);
+      }
     }
+    core.endGroup();
   }
   catch (error) {
     core.setFailed(error.message);