Generate key.

action.yml

@@ -22,6 +22,10 @@ outputs:
     description: 'The generated cache key used.'
   cache-hit:
     description: 'Indicates an exact match was found for the cache key.'
+  rust-version:
+    description: 'Version of the installed rustc.'
+  rust-hash:
+    description: 'Commit hash of the installed rustc.'
 runs:
   using: 'node16'
   main: 'dist/index.js'

index.ts

@@ -5,6 +5,7 @@ import * as exec from '@actions/exec';
 import * as tc from '@actions/tool-cache';
 import TOML from '@ltd/j-toml';
 import { CACHE_ENABLED, CARGO_HOME, restoreCache } from './src/cargo';
+import { extractRustVersion } from './src/rust';
 
 interface Toolchain {
 	channel: string;
@@ -118,7 +119,7 @@ async function installToolchain(toolchain: Toolchain) {
 
 	core.info('Logging installed toolchain versions');
 
-	await exec.exec('rustc', [`+${toolchain.channel}`, '--version', '--verbose']);
+	await extractRustVersion(toolchain.channel);
 }
 
 async function downloadAndInstallBinstall(binDir: string) {
@@ -199,9 +200,12 @@ async function run() {
 	core.exportVariable('CARGO_TERM_COLOR', 'always');
 
 	try {
-		await restoreCache();
 		await installToolchain(detectToolchain());
 		await installBins();
+
+		// Restore cache after the toolchain has been installed,
+		// as we use the rust version and commit hashes in the cache key!
+		await restoreCache();
 	} catch (error: unknown) {
 		core.setFailed((error as Error).message);
 

src/cargo.ts

@@ -1,5 +1,6 @@
 /* eslint-disable node/no-unsupported-features/node-builtins */
 
+import crypto from 'crypto';
 import fs from 'fs';
 import os from 'os';
 import path from 'path';
@@ -13,12 +14,45 @@ export const CARGO_HOME = process.env.CARGO_HOME || path.join(os.homedir(), '.ca
 
 export const CACHE_ENABLED = core.getBooleanInput('cache') || cache.isFeatureAvailable();
 
-export function getPrimaryCacheKey(): string {
+let CACHE_KEY = '';
-	return `setup-rustcargo-${process.platform}`;
+
+export async function getPrimaryCacheKey() {
+	if (CACHE_KEY) {
+		return CACHE_KEY;
+	}
+
+	core.info('Generating cache key');
+
+	const rustVersion = core.getState('rust-version');
+
+	core.debug(`Hashing Rust version = ${rustVersion}`);
+
+	const rustHash = core.getState('rust-hash');
+
+	core.debug(`Hashing Rust commit hash = ${rustHash}`);
+
+	const lockHash = await glob.hashFiles('Cargo.lock');
+
+	core.debug(`Hashing Cargo.lock = ${lockHash}`);
+
+	const hasher = crypto.createHash('sha1');
+	hasher.update(rustVersion);
+	hasher.update(rustHash);
+	hasher.update(lockHash);
+
+	// eslint-disable-next-line require-atomic-updates
+	CACHE_KEY = `setup-rustcargo-${process.platform}-${hasher.digest('hex')}`;
+
+	return CACHE_KEY;
 }
 
 export function getPathsToCache(): string[] {
-	return [path.join(CARGO_HOME, 'registry')];
+	return [
+		// ~/.cargo/registry
+		path.join(CARGO_HOME, 'registry'),
+		// /workspace/target/debug
+		path.join(process.cwd(), 'target/debug'),
+	];
 }
 
 export async function cleanCargoRegistry() {
@@ -45,7 +79,7 @@ export async function saveCache() {
 		return;
 	}
 
-	const primaryKey = getPrimaryCacheKey();
+	const primaryKey = await getPrimaryCacheKey();
 	const cacheHitKey = core.getState('cache-hit-key');
 
 	if (cacheHitKey === primaryKey) {

src/rust.ts

@@ -0,0 +1,31 @@
+import * as core from '@actions/core';
+import * as exec from '@actions/exec';
+
+export async function extractRustVersion(toolchain: string) {
+	let out = '';
+
+	await exec.exec('rustc', [`+${toolchain}`, '--version', '--verbose'], {
+		listeners: {
+			stdout(data: Buffer) {
+				out += data.toString();
+			},
+		},
+	});
+
+	out.split('\n').forEach((line) => {
+		let key = '';
+
+		if (line.startsWith('commit-hash')) {
+			key = 'rust-hash';
+		} else if (line.startsWith('release')) {
+			key = 'rust-version';
+		} else {
+			return;
+		}
+
+		const value = line.split(':')[1].trim();
+
+		core.saveState(key, value);
+		core.setOutput(key, value);
+	});
+}