Allow save-only/restore-only cache runs

Add an option to restore a cache without creating a new one, or to
create a cache without restoring an old one.  This is useful in the
scenario where the action is called multiple times in a run, as it
allows the cache to only be restored on the first call, and for a new
cache to only be written on the last call.

This option replaces the `package-cache-key` option; as discussed in cygwin#6
that option isn't very useful.

Additionally, add some more scopes to the cache name.  Without this
change, a second attempt to create a cache in the same action run (e.g.
because one step installs some packages, then another step installs some
more) will fail because of the cache name collision.

Also update the README and tests, although the tests are only getting a
very quick update for this function, as I'm going to do a much more
comprehensive test update separately.

.github/workflows/test.yml

@@ -241,7 +241,7 @@ jobs:
         uses: ./
         with:
           packages: bash-completion
-          package-cache-key: testing-cache
+          cache: enabled
           add-to-path: false
       - name: Delete Cygwin installation and cache
         run: |
@@ -250,7 +250,7 @@ jobs:
       - name: Reinstall Cygwin only
         uses: ./
         with:
-          package-cache-key: testing-cache
+          cache: enabled
           add-to-path: false
       - name: Find bash-completion in the package cache
         shell: C:\cygwin\bin\bash.exe --noprofile --norc -e -o pipefail -o igncr {0}

README.md

@@ -26,7 +26,7 @@ Parameters
 | site        | http://mirrors.kernel.org/sourceware/cygwin/ | Mirror site to install from
 | check-sig   | true                                         | Whether to check the setup.ini signature
 | add-to-path | true                                         | Whether to add Cygwin's `/bin` directory to the system `PATH`
-| package-cache-key | ''                                     | The key to use for caching downloaded packages.
+| cache       | disabled                                     | Whether to cache the package downloads
 
 Line endings
 ------------
@@ -91,9 +91,8 @@ Caching
 
 If you're likely to do regular builds, you might want to store the packages
 locally rather than needing to download them from the Cygwin mirrors on every
-build.  Set `package-cache-key` to some string (e.g. `cygwin-package-cache`),
-and the action will use [GitHub's dependency caching][0] to store downloaded
-package files between runs.
+build.  Set `cache` to `enabled` and the action will use [GitHub's dependency
+caching][0] to store downloaded package files between runs.
 
 [0]: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows
 
@@ -102,6 +101,25 @@ expense of taking slightly longer before and after the installation to check
 and potentially update the cache.  The installer will still check for updated
 packages, and will download new packages if the cached ones are out of date
 
+In certain circumstances you might want to ignore any existing caches but still
+store a new one, or restore a cache but not write one.  Do this by setting
+`cache` to `saveonly` or `restoreonly` as appropriate.  This is particularly
+useful when calling the action multiple times in the same run, where you
+probably want to restore the cache the first time the action is called, then
+save it the last time it is called.
+
+You should make sure to clear these caches every so often.  This action, like
+the underlying Cygwin installer, doesn't remove old package files from its
+download directory, so if you don't clear the caches occasionally (and you run
+builds often enough that GitHub doesn't do it for you automatically) you'll
+find the caches keep getting larger as they gain more and more outdated and
+unused packages.  Either [delete them manually][1], [use a separate action or
+API call][2], or do occasional runs with `saveonly` to create a fresher small
+cache.
+
+[1]: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#deleting-cache-entries
+[2]: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#deleting-cache-entries
+
 Mirrors and signatures
 ----------------------
 

action.yml

@@ -26,10 +26,10 @@ inputs:
     description: Should Cygwin's bin directory be added to the system PATH?
     required: false
     default: true
-  package-cache-key:
-    description: Key prefix to use for package caches
+  cache:
+    description: Cache package downloads for speed
     required: false
-    default: ''
+    default: disabled
 
 runs:
   using: "composite"
@@ -41,15 +41,17 @@ runs:
       run: Write-Output "GIT_BASH_PATH=$($(Get-Command bash).Source)" >> $Env:GITHUB_ENV
 
     - uses: actions/cache/restore@v3
-      if: inputs.package-cache-key != ''
+      if: inputs.cache == 'enabled' || inputs.cache == 'restoreonly'
       with:
-        key: ${{ inputs.package-cache-key }}-${{ github.run_id }}-${{ github.run_attempt }}
+        key: cygwin-install-action-packages-${{ github.run_id }}-${{ github.run_attempt }}-${{ github.job }}-${{ github.action }}
         path: C:\cygwin-packages
         restore-keys:
-          ${{ inputs.package-cache-key }}-${{ github.run_id }}-
-          ${{ inputs.package-cache-key }}-
+          cygwin-install-action-packages-${{ github.run_id }}-${{ github.job }}-${{ github.run_attempt }}-
+          cygwin-install-action-packages-${{ github.run_id }}-${{ github.job }}-
+          cygwin-install-action-packages-${{ github.run_id }}-
+          cygwin-install-action-packages-
 
-    - if: inputs.package-cache-key != ''
+    - if: inputs.cache == 'enabled' || inputs.cache == 'restoreonly'
       working-directory: C:\
       shell: ${{ env.GIT_BASH_PATH }} --noprofile --norc -eo pipefail {0}
       run: |
@@ -111,7 +113,7 @@ runs:
         & C:\setup.exe $args | Out-Default
       shell: powershell
 
-    - if: inputs.package-cache-key != ''
+    - if: inputs.cache == 'enabled' || inputs.cache == 'saveonly'
       id: refresh-cache
       working-directory: C:\
       shell: ${{ env.GIT_BASH_PATH }} --noprofile --norc -eo pipefail {0}
@@ -128,7 +130,7 @@ runs:
     - if: steps.refresh-cache.outputs.update_package_cache != ''
       uses: actions/cache/save@v3
       with:
-        key: ${{ inputs.package-cache-key }}-${{ github.run_id }}-${{ github.run_attempt }}
+        key: cygwin-install-action-packages-${{ github.run_id }}-${{ github.run_attempt }}-${{ github.job }}-${{ github.action }}
         path: C:\cygwin-packages
 
     - if: ${{ inputs.add-to-path  == 'true' }}