Expose Python runtime identity for downstream caching

src/setup-uv.ts

@@ -16,7 +16,7 @@ import {
   getPlatform,
   type Platform,
 } from "./utils/platforms";
-import { getResolvedPythonVersion } from "./utils/python-version";
+import { getPythonRuntimeId } from "./utils/python-runtime";
 import { resolveUvVersion } from "./version/resolve";
 
 const sourceDir = __dirname;
@@ -102,10 +102,7 @@ async function run(): Promise<void> {
 
     const detectedPythonVersion = await getPythonVersion(inputs);
     core.setOutput("python-version", detectedPythonVersion);
-    core.setOutput(
-      "python-version-resolved",
-      await getResolvedPythonVersion(inputs),
-    );
+    core.setOutput("python-runtime-id", await getPythonRuntimeId(inputs));
 
     if (inputs.enableCache) {
       await restoreCache(inputs, detectedPythonVersion);

src/utils/python-runtime.ts

@@ -0,0 +1,85 @@
+import { join } from "node:path";
+import * as core from "@actions/core";
+import * as exec from "@actions/exec";
+import type { SetupInputs } from "./inputs";
+
+const PYTHON_RUNTIME_QUERY = `
+import json
+import platform
+import sys
+import sysconfig
+
+print(json.dumps({
+    "implementation": sys.implementation.name,
+    "implementationVersion": list(sys.implementation.version),
+    "pythonVersion": platform.python_version(),
+    "freethreaded": sysconfig.get_config_var("Py_GIL_DISABLED") == 1,
+}))
+`;
+
+type ReleaseLevel = "alpha" | "beta" | "candidate" | "final";
+
+interface PythonRuntime {
+  implementation: string;
+  implementationVersion: [number, number, number, ReleaseLevel, number];
+  pythonVersion: string;
+  freethreaded: boolean;
+}
+
+function formatRuntimeId(runtime: PythonRuntime): string {
+  if (
+    typeof runtime.implementation !== "string" ||
+    runtime.implementation === "" ||
+    typeof runtime.pythonVersion !== "string" ||
+    runtime.pythonVersion === "" ||
+    typeof runtime.freethreaded !== "boolean"
+  ) {
+    throw new Error("Invalid Python runtime metadata");
+  }
+
+  let id = `cpython-${runtime.pythonVersion}`;
+  if (runtime.implementation !== "cpython") {
+    const [major, minor, micro, releaseLevel, serial] =
+      runtime.implementationVersion;
+    const suffixes = { alpha: "a", beta: "b", candidate: "rc", final: "" };
+    const suffix = suffixes[releaseLevel];
+    if (
+      suffix === undefined ||
+      ![major, minor, micro, serial].every(
+        (part) => Number.isInteger(part) && part >= 0,
+      )
+    ) {
+      throw new Error("Invalid Python implementation version");
+    }
+    const implementationVersion = `${major}.${minor}.${micro}${suffix}${suffix ? serial : ""}`;
+    id = `${runtime.implementation}-${implementationVersion}-python-${runtime.pythonVersion}`;
+  }
+
+  return runtime.freethreaded ? `${id}-freethreaded` : id;
+}
+
+export async function getPythonRuntimeId(inputs: SetupInputs): Promise<string> {
+  if (!inputs.activateEnvironment) {
+    return "";
+  }
+
+  const pythonPath =
+    process.platform === "win32"
+      ? join(inputs.venvPath, "Scripts", "python.exe")
+      : join(inputs.venvPath, "bin", "python");
+
+  try {
+    // @actions/exec parses the executable as a command line, so quote the path.
+    const { stdout } = await exec.getExecOutput(
+      `"${pythonPath.replace(/"/g, '\\"')}"`,
+      ["-I", "-c", PYTHON_RUNTIME_QUERY],
+      { silent: !core.isDebug() },
+    );
+    return formatRuntimeId(JSON.parse(stdout));
+  } catch (error) {
+    core.debug(
+      `Failed to identify the activated environment's Python runtime. Error: ${error instanceof Error ? error.message : String(error)}`,
+    );
+    return "";
+  }
+}

src/utils/python-version.ts

@@ -1,32 +0,0 @@
-import { join } from "node:path";
-import * as core from "@actions/core";
-import * as exec from "@actions/exec";
-import type { SetupInputs } from "./inputs";
-
-export async function getResolvedPythonVersion(
-  inputs: SetupInputs,
-): Promise<string> {
-  if (!inputs.activateEnvironment) {
-    return "";
-  }
-
-  const pythonPath =
-    process.platform === "win32"
-      ? join(inputs.venvPath, "Scripts", "python.exe")
-      : join(inputs.venvPath, "bin", "python");
-
-  try {
-    // @actions/exec parses the executable as a command line, so quote the path.
-    const { stdout } = await exec.getExecOutput(
-      `"${pythonPath.replace(/"/g, '\\"')}"`,
-      ["-I", "-c", "import platform; print(platform.python_version())"],
-      { silent: !core.isDebug() },
-    );
-    return stdout.trim();
-  } catch (error) {
-    core.debug(
-      `Failed to get the activated environment's Python version. Error: ${error instanceof Error ? error.message : String(error)}`,
-    );
-    return "";
-  }
-}