add support for python-version-file

.github/workflows/test-python.yml

@@ -10,6 +10,7 @@ on:
       - '**.md'
   schedule:
     - cron: 30 3 * * *
+  workflow_dispatch:
 
 jobs:
   default-version:
@@ -62,6 +63,39 @@ jobs:
     - name: Run simple code
       run: python -c 'import math; print(math.factorial(5))'
 
+  setup-versions-from-file:
+    name: Setup ${{ matrix.python }} ${{ matrix.os }} version file
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [macos-latest, windows-latest, ubuntu-18.04, ubuntu-20.04]
+        python: [3.5.4, 3.6.7, 3.7.5, 3.8.1]
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+
+    - name: build-version-file ${{ matrix.python }}
+      run: echo ${{ matrix.python }} > .python-version
+
+    - name: setup-python ${{ matrix.python }}
+      uses: ./
+      with:
+        python-version-file: '.python-version'
+
+    - name: Validate version
+      run: |
+        $pythonVersion = (python --version)
+        if ("Python ${{ matrix.python }}" -ne "$pythonVersion"){
+          Write-Host "The current version is $pythonVersion; expected version is ${{ matrix.python }}"
+          exit 1
+        }
+        $pythonVersion
+      shell: pwsh
+
+    - name: Run simple code
+      run: python -c 'import math; print(math.factorial(5))'
+
   setup-pre-release-version-from-manifest:
     name: Setup 3.9.0-beta.4 ${{ matrix.os }}
     runs-on: ${{ matrix.os }}

README.md

@@ -20,6 +20,7 @@ This action sets up a Python environment for use in actions by:
 - Support for pre-release versions of Python.
 - Support for installing any version of PyPy on-flight
 - Support for built-in caching of pip and pipenv dependencies
+- Support for `.python-version` file
 
 # Usage
 
@@ -36,6 +37,17 @@ steps:
 - run: python my_script.py
 ```
 
+Read Python version from file:
+```yaml
+steps:
+- uses: actions/checkout@v2
+- uses: actions/setup-python@v2
+  with:
+    python-version-file: '.python-version' # Read python version from a file
+    architecture: 'x64' # optional x64 or x86. Defaults to x64 if not specified
+- run: python my_script.py
+```
+
 Matrix Testing:
 ```yaml
 jobs:

action.yml

@@ -6,6 +6,8 @@ inputs:
   python-version:
     description: "Version range or exact version of a Python version to use, using SemVer's version range syntax."
     default: '3.x'
+  python-version-file:
+    description: "File containing the Python version to use.  Examples: .python-version"
   cache:
     description: 'Used to specify a package manager for caching in the default directory. Supported values: pip, pipenv.'
     required: false

dist/setup/index.js

@@ -6622,12 +6622,16 @@ var __importStar = (this && this.__importStar) || function (mod) {
     result["default"] = mod;
     return result;
 };
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
 Object.defineProperty(exports, "__esModule", { value: true });
 const core = __importStar(__webpack_require__(470));
 const finder = __importStar(__webpack_require__(927));
 const finderPyPy = __importStar(__webpack_require__(50));
 const path = __importStar(__webpack_require__(622));
 const os = __importStar(__webpack_require__(87));
+const fs_1 = __importDefault(__webpack_require__(747));
 const cache_factory_1 = __webpack_require__(633);
 const utils_1 = __webpack_require__(163);
 function isPyPyVersion(versionSpec) {
@@ -6643,10 +6647,23 @@ function cacheDependencies(cache, pythonVersion) {
         yield cacheDistributor.restoreCache();
     });
 }
+function resolveVersionInput() {
+    let version = core.getInput('python-version');
+    const versionFileInput = core.getInput('python-version-file');
+    if (versionFileInput) {
+        const versionFilePath = path.join(process.env.GITHUB_WORKSPACE, versionFileInput);
+        if (!fs_1.default.existsSync(versionFilePath)) {
+            throw new Error(`The specified node version file at: ${versionFilePath} does not exist`);
+        }
+        version = fs_1.default.readFileSync(versionFilePath, 'utf8');
+        core.info(`Resolved ${versionFileInput} as ${version}`);
+    }
+    return version;
+}
 function run() {
     return __awaiter(this, void 0, void 0, function* () {
         try {
-            const version = core.getInput('python-version');
+            const version = resolveVersionInput();
             if (version) {
                 let pythonVersion;
                 const arch = core.getInput('architecture') || os.arch();

src/setup-python.ts

@@ -3,6 +3,7 @@ import * as finder from './find-python';
 import * as finderPyPy from './find-pypy';
 import * as path from 'path';
 import * as os from 'os';
+import fs from 'fs';
 import {getCacheDistributor} from './cache-distributions/cache-factory';
 import {isGhes} from './utils';
 
@@ -24,9 +25,30 @@ async function cacheDependencies(cache: string, pythonVersion: string) {
   await cacheDistributor.restoreCache();
 }
 
+function resolveVersionInput(): string {
+  let version = core.getInput('python-version');
+  const versionFileInput = core.getInput('python-version-file');
+
+  if (versionFileInput) {
+    const versionFilePath = path.join(
+      process.env.GITHUB_WORKSPACE!,
+      versionFileInput
+    );
+    if (!fs.existsSync(versionFilePath)) {
+      throw new Error(
+        `The specified node version file at: ${versionFilePath} does not exist`
+      );
+    }
+    version = fs.readFileSync(versionFilePath, 'utf8');
+    core.info(`Resolved ${versionFileInput} as ${version}`);
+  }
+
+  return version;
+}
+
 async function run() {
   try {
-    const version = core.getInput('python-version');
+    const version = resolveVersionInput();
     if (version) {
       let pythonVersion: string;
       const arch: string = core.getInput('architecture') || os.arch();