Cache python installs (#621)

This pull request introduces support for caching Python installs in the
GitHub Action, allowing users to cache not only dependencies but also
the Python interpreter itself.

This works by setting the `UV_PYTHON_INSTALL_DIR` to a subdirectory of
the dependency cache path so that Python installs are directed there.

Fixes #135

---------

Co-authored-by: Kevin Stillhammer <kevin.stillhammer@gmail.com>

src/cache/restore-cache.ts

@@ -5,7 +5,9 @@ import { hashFiles } from "../hash/hash-files";
 import {
   cacheDependencyGlob,
   cacheLocalPath,
+  cachePython,
   cacheSuffix,
+  getUvPythonDir,
   pruneCache,
   pythonVersion as pythonVersionInput,
   restoreCache as shouldRestoreCache,
@@ -30,8 +32,12 @@ export async function restoreCache(): Promise<void> {
   core.info(
     `Trying to restore uv cache from GitHub Actions cache with key: ${cacheKey}`,
   );
+  const cachePaths = [cacheLocalPath];
+  if (cachePython) {
+    cachePaths.push(await getUvPythonDir());
+  }
   try {
-    matchedKey = await cache.restoreCache([cacheLocalPath], cacheKey);
+    matchedKey = await cache.restoreCache(cachePaths, cacheKey);
   } catch (err) {
     const message = (err as Error).message;
     core.warning(message);
@@ -62,7 +68,8 @@ async function computeKeys(): Promise<string> {
   const pythonVersion = await getPythonVersion();
   const platform = await getPlatform();
   const pruned = pruneCache ? "-pruned" : "";
-  return `setup-uv-${CACHE_VERSION}-${getArch()}-${platform}-${pythonVersion}${pruned}${cacheDependencyPathHash}${suffix}`;
+  const python = cachePython ? "-py" : "";
+  return `setup-uv-${CACHE_VERSION}-${getArch()}-${platform}-${pythonVersion}${pruned}${python}${cacheDependencyPathHash}${suffix}`;
 }
 
 async function getPythonVersion(): Promise<string> {

src/save-cache.ts

@@ -10,7 +10,9 @@ import {
 import { STATE_UV_PATH, STATE_UV_VERSION } from "./utils/constants";
 import {
   cacheLocalPath,
+  cachePython,
   enableCache,
+  getUvPythonDir,
   ignoreNothingToCache,
   pruneCache as shouldPruneCache,
   saveCache as shouldSaveCache,
@@ -68,8 +70,22 @@ async function saveCache(): Promise<void> {
       `Cache path ${actualCachePath} does not exist on disk. This likely indicates that there are no dependencies to cache. Consider disabling the cache input if it is not needed.`,
     );
   }
+
+  const cachePaths = [actualCachePath];
+  if (cachePython) {
+    const pythonDir = await getUvPythonDir();
+    core.info(`Including Python cache path: ${pythonDir}`);
+    if (!fs.existsSync(pythonDir) && !ignoreNothingToCache) {
+      throw new Error(
+        `Python cache path ${pythonDir} does not exist on disk. This likely indicates that there are no dependencies to cache. Consider disabling the cache input if it is not needed.`,
+      );
+    }
+    cachePaths.push(pythonDir);
+  }
+
+  core.info(`Final cache paths: ${cachePaths.join(", ")}`);
   try {
-    await cache.saveCache([actualCachePath], cacheKey);
+    await cache.saveCache(cachePaths, cacheKey);
     core.info(`cache saved with the key: ${cacheKey}`);
   } catch (e) {
     if (

src/utils/inputs.ts

@@ -1,5 +1,6 @@
 import path from "node:path";
 import * as core from "@actions/core";
+import * as exec from "@actions/exec";
 import { getConfigValueFromTomlFile } from "./config-file";
 
 export const workingDirectory = core.getInput("working-directory");
@@ -15,6 +16,7 @@ export const cacheSuffix = core.getInput("cache-suffix") || "";
 export const cacheLocalPath = getCacheLocalPath();
 export const cacheDependencyGlob = getCacheDependencyGlob();
 export const pruneCache = core.getInput("prune-cache") === "true";
+export const cachePython = core.getInput("cache-python") === "true";
 export const ignoreNothingToCache =
   core.getInput("ignore-nothing-to-cache") === "true";
 export const ignoreEmptyWorkdir =
@@ -123,6 +125,25 @@ function getCacheDirFromConfig(): string | undefined {
   return undefined;
 }
 
+export async function getUvPythonDir(): Promise<string> {
+  if (process.env.UV_PYTHON_INSTALL_DIR !== undefined) {
+    core.info(
+      `Using UV_PYTHON_INSTALL_DIR from environment: ${process.env.UV_PYTHON_INSTALL_DIR}`,
+    );
+    return process.env.UV_PYTHON_INSTALL_DIR;
+  }
+  core.info("Determining uv python dir using `uv python dir`...");
+  const result = await exec.getExecOutput("uv", ["python", "dir"]);
+  if (result.exitCode !== 0) {
+    throw new Error(
+      `Failed to get uv python dir: ${result.stderr || result.stdout}`,
+    );
+  }
+  const dir = result.stdout.trim();
+  core.info(`Determined uv python dir: ${dir}`);
+  return dir;
+}
+
 function getCacheDependencyGlob(): string {
   const cacheDependencyGlobInput = core.getInput("cache-dependency-glob");
   if (cacheDependencyGlobInput !== "") {