Turn off caching for the full flavor by default

Some testing reveals that the 64-bit and the 32-bit `full` SDK weigh in
with ~1,300MB and ~915MB at time of writing, respectively. Packing and
saving these to the cache takes a long time: ~5m20s and ~2m45s.

Given that the non-cached download takes ~8m20s and ~6m, respectively,
and restoring the artifacts from cache takes ~8m15s and ~5m (which is
not a lot faster, not by a long stretch), it is neither worth the time
nor the disk space to cache the `full` SDKs.

Let's introduce a new default value for the input parameter `cache`,
`auto`, that turns on caching except for the `full` flavor.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

README.md

@@ -70,6 +70,8 @@ By default, this Action prints a line whenever 250 items were extracted (this do
 
 To accelerate this Action, artifacts are cached once downloaded. This can be turned off by setting the input parameter `cache` to `false`.
 
+In practice, caching the `full` artifacts does not provide much of a speed-up. Instead, it slows it down by adding several minutes during with the artifact is cached. Therefore, caching is disabled for the `full` artifacts by default, corresponding to `cache: auto`.
+
 ## Developing _this_ Action
 
 > First, you'll need to have a reasonably modern version of `node` handy, such as Node 12.

action.yml

@@ -21,7 +21,7 @@ inputs:
   cache:
     required: false
     description: 'Use @actions/cache to accelerate this Action'
-    default: 'true'
+    default: 'auto'
 runs:
   using: 'node12'
   main: 'dist/index.js'

main.ts

@@ -17,7 +17,17 @@ async function run(): Promise<void> {
 
     const {artifactName, download, id} = await get(flavor, architecture)
     const outputDirectory = core.getInput('path') || `C:/${artifactName}`
-    let useCache = core.getInput('cache') === 'true'
+    let useCache: boolean
+    switch (core.getInput('cache')) {
+      case 'true':
+        useCache = true
+        break
+      case 'auto':
+        useCache = flavor !== 'full'
+        break
+      default:
+        useCache = false
+    }
 
     try {
       if (useCache && (await restoreCache([outputDirectory], id))) {