Set up automatic pre-release builds from dev branch

.github/workflows/build.yml

@@ -96,16 +96,16 @@ jobs:
       - name: Run cyclomatic complexity check
         run: radon cc --show-complexity --average --order SCORE requests_cache
 
-  # Deploy stable builds on tags only
+  # Deploy pre-release builds from dev branch, and stable builds on tags only
   release:
     needs: [test, analyze]
-    if: startsWith(github.ref, 'refs/tags/v')
+    if: startsWith(github.ref, 'refs/tags/v') || github.ref == 'refs/heads/dev'
     runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: '3.8'
+          python-version: ${{ env.LATEST_PY_VERSION }}
 
       - name: Install dependencies
         run: pip install -U ".[build]"

CONTRIBUTING.md

@@ -145,3 +145,12 @@ Release steps:
 - Push a new tag, e.g.: `git tag v0.1 && git push origin --tags`
 - This will trigger a deployment. Verify that this completes successfully and that the new version
   can be installed from pypi with `pip install`
+
+## Pre-Releases
+Pre-release builds are convenient for letting testers try out in-development changes. Versions with
+the suffix `.dev` (among others) can be deployed to PyPI and installed by users with `pip install --pre`,
+and are otherwise ignored by `pip install`. See python packaging docs on
+[pre-release versioning](https://packaging.python.org/guides/distributing-packages-using-setuptools/#pre-release-versioning)
+for more details.
+
+A pre-release build for requests-cache will automatically be published for **any commits to the dev branch.**

pyproject.toml

@@ -11,6 +11,9 @@ directory = 'test-reports'
 [tool.coverage.run]
 branch = true
 source = ['requests_cache']
+omit = [
+    'requests_cache/__init__.py',
+]
 
 [tool.isort]
 profile = "black"

requests_cache/__init__.py

@@ -1,5 +1,8 @@
 # flake8: noqa: E402,F401
-__version__ = '0.6.2'
+from logging import getLogger
+from os import getenv
+
+__version__ = '0.6.3'
 
 try:
     from .response import AnyResponse, CachedHTTPResponse, CachedResponse, ExpirationTime
@@ -17,3 +20,18 @@
 # Quietly ignore ImportError, if setup.py is invoked outside a virtualenv
 except ImportError:
     pass
+
+
+def get_prerelease_version(version: str) -> str:
+    """If we're running in a GitHub Action job on the dev branch, get a prerelease semantic version
+    using the current build number. For example: ``1.0.0 -> 1.0.0-dev.123``
+    """
+    if getenv('GITHUB_REF') == 'refs/heads/dev':
+        build_number = getenv('GITHUB_RUN_NUMBER', '0')
+        version = f'{version}.dev{build_number}'
+        getLogger(__name__).info(f'Using pre-release version: {version}')
+    return version
+
+
+# This won't modify the version outside of a GitHub Action
+__version__ = get_prerelease_version(__version__)