✨ Implement initial action logic

Author: webknjaz

action.yml

@@ -0,0 +1,126 @@
+---
+
+name: cache-python-deps
+description: >-
+  A GitHub Action maintaining caches dependent on Python runtime
+  and ABI stability.
+
+inputs:
+  cache-directory-lookup-command:
+    description: A command that prints cache directory to standard output.
+    default: python -Im pip cache dir
+    required: false
+  cache-key-for-dependency-files:
+    description: >-
+      A cache key string derived from the dependency declaration files.
+    required: true
+
+outputs:
+  cache-directory-path:
+    description: The discovered cache directory path.
+    value: ${{ steps.cache-dir.outputs.dir }}
+  cache-key-for-os:
+    description: >-
+      A cache key string derived from the current OS and interpreter stability.
+    value: >-
+      ${{ steps.python-runtime.outputs.restore-key-fallback-prefix }}
+  cache-key-for-dependencies:
+    description: >-
+      A cache key string derived from the current interpreter version
+      and the dependency file hashes.
+    value: >-
+      ${{ steps.python-runtime.outputs.cache-entry-key }}
+  cache-key-for-python-interpreter:
+    description: >-
+      A cache key string derived from the current interpreter version.
+    value: >-
+      ${{ steps.python-runtime.outputs.restore-key-prefix }}
+  is-stable-abi:
+    description: >-
+      Whether the currently used Python version has a reliable
+      Application Binary Interface. If it doesn't, it's best to avoid
+      caching any dependencies.
+    value: ${{ steps.python-runtime.outputs.is-stable-abi }}
+
+runs:
+  using: composite
+  steps:
+  - name: >-
+      Calculate Python interpreter properties version hash value
+      for use in the cache key
+    id: python-runtime
+    run: |
+      # Determining the Python runtime features...
+
+      from hashlib import sha512
+      from os import environ
+      from sys import version, version_info
+
+      FILE_APPEND_MODE = 'a'
+
+      is_stable_abi = version_info.releaselevel == 'final'
+      version_hash = sha512(version.encode()).hexdigest()
+
+      stable_or_unstable = f'{"" if is_stable_abi else "un"}stable'
+      restore_key_fallback_prefix = (
+          f'${{ runner.os }}-python-dep-cache-{stable_or_unstable}'
+      )
+      restore_key_prefix = f'{restore_key_fallback_prefix}-{version_hash}'
+      cache_entry_key = (
+          f'{restore_key_prefix}-{version_hash}-'
+          '${{ inputs.cache-key-for-dependency-files }}'
+      )
+
+      print(f'Python ABI is found to be {stable_or_unstable}.')
+      print(f'Python version-derived hash is {version_hash}.')
+      print(f'The computed cache entry key is {cache_entry_key}.')
+
+      with open(
+              environ['GITHUB_OUTPUT'], mode=FILE_APPEND_MODE,
+      ) as outputs_file:
+          print(
+              'is-stable-abi={is_stable_abi}'.
+              format(is_stable_abi=str(is_stable_abi).lower()),
+              file=outputs_file,
+          )
+          print(
+              f'restore-key-fallback-prefix={restore_key_fallback_prefix}',
+              file=outputs_file,
+          )
+          print(
+              f'restore-key-prefix={restore_key_prefix}',
+              file=outputs_file,
+          )
+          print(f'cache-entry-key={cache_entry_key}', file=outputs_file)
+    shell: python
+  - name: Get cache dir
+    id: cache-dir
+    run: >
+      # Discovering cache directory...
+
+      echo "dir=$(${{ inputs.cache-directory-lookup-command }})"
+      >> "${GITHUB_OUTPUT}"
+    shell: bash
+  - name: Skip setting up cache
+    if: >-
+      !fromJSON(steps.python-runtime.outputs.is-stable-abi)
+    run: >
+      # Skipping cache configuration because due to unstable Python ABI...
+
+
+      >&2 echo Skipping cache configuration because the current
+      Python ABI is unstable...
+    shell: bash
+  - name: Set up cache
+    if: fromJSON(steps.python-runtime.outputs.is-stable-abi)
+    uses: actions/cache@v4
+    with:
+      path: ${{ steps.cache-dir.outputs.dir }}
+      key: >-
+        ${{ steps.python-runtime.outputs.cache-entry-key }}
+      restore-keys: |
+        ${{ steps.python-runtime.outputs.cache-entry-key }}
+        ${{ steps.python-runtime.outputs.restore-key-prefix }}
+        ${{ steps.python-runtime.outputs.restore-key-fallback-prefix }}
+
+...