Add automatic toolchain version detection

.github/workflows/test-latest.yml

@@ -53,3 +53,34 @@ jobs:
           version: latest
       - run: rye sync
         working-directory: __tests__/fixtures/rye-project
+
+  test-latest-automatic-toolchain:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, macos-14, oracle-aarch64]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Determine expected python version
+        id: determine-expected-python-version
+        run: |
+          EXPECTED_PYTHON_VERSION=$(cat .python-version)
+          echo "EXPECTED_PYTHON_VERSION=$EXPECTED_PYTHON_VERSION" >> "$GITHUB_OUTPUT"
+        working-directory: __tests__/fixtures/rye-project
+      - name: Setup rye
+        uses: ./
+        with:
+          version: latest
+          working-directory: __tests__/fixtures/rye-project
+      - run: rye sync
+        working-directory: __tests__/fixtures/rye-project
+      - name: Check python version
+        run: |
+          ACTUAL_PYTHON_VERSION=$(ls $RYE_HOME/py)
+          if [ "$ACTUAL_PYTHON_VERSION" != "$EXPECTED_PYTHON_VERSION" ];
+          then
+            echo "$ACTUAL_PYTHON_VERSION is not the same as $EXPECTED_PYTHON_VERSION"
+            exit 1
+          fi
+        env:
+          EXPECTED_PYTHON_VERSION: ${{ steps.determine-expected-python-version.outputs.EXPECTED_PYTHON_VERSION }}

src/setup-rye.ts

@@ -5,7 +5,7 @@ import * as io from '@actions/io'
 import * as path from 'path'
 import * as fs from 'fs'
 import {downloadVersion, tryGetFromCache} from './download/download-version'
-import {restoreCache} from './restore-cache'
+import {restoreCache, workingDir} from './restore-cache'
 import {
   Architecture,
   EARLIEST_VERSION_WITH_NO_MODIFY_PATHSUPPORT,
@@ -103,13 +103,18 @@ async function installRye(
   core.debug(`Created temporary directory ${tempDir}`)
   // Cache first to get the correct path
   const cachedPath = await tc.cacheDir(tempDir, toolsCacheName, version, arch)
+  const toolchainVersion = await determineToolchainVersion()
+  const env = toolchainVersion
+    ? {
+        ...process.env,
+        RYE_HOME: cachedPath,
+        RYE_TOOLCHAIN_VERSION: toolchainVersion
+      }
+    : {...process.env, RYE_HOME: cachedPath}
   const options: exec.ExecOptions = {
     cwd: cachedPath,
     silent: !core.isDebug(),
-    env: {
-      ...process.env,
-      RYE_HOME: cachedPath
-    }
+    env: env
   }
   core.info(`Installing Rye into ${cachedPath}`)
   const execArgs = ['self', 'install', '--yes']
@@ -122,6 +127,22 @@ async function installRye(
   return cachedPath
 }
 
+async function determineToolchainVersion(): Promise<string | void> {
+  const pythonVersionFile = `${workingDir}${path.sep}.python_version`
+  if (fs.existsSync(pythonVersionFile)) {
+    const toolchainVersion = await fs.promises.readFile(
+      pythonVersionFile,
+      'utf8'
+    )
+    core.info(`Determined RYE_TOOLCHAIN_VERSION: ${toolchainVersion}`)
+    return toolchainVersion
+  }
+  core.warning(
+    `No .python_version file found, using default RYE_TOOLCHAIN_VERSION`
+  )
+  return
+}
+
 async function createConfigBackup(installedPath: string): Promise<void> {
   if (fs.existsSync(`${installedPath}${path.sep}${RYE_CONFIG_TOML}`)) {
     await io.cp(