perf: overlap compiler identity and native driver discovery (#634)

packages/compiler/src/index.ts

@@ -708,9 +708,20 @@ async function compileTracked(
     : null;
   let earlyCacheOptions: EarlyExecutableCacheOptions | null = null;
   if (outputKind === "exe") {
-    const implementation = await compilerImplementationIdentity();
     const helperObjectRoute = opts.nativeProgramObject === true ||
       (usesPrecompiledRuntimePack(opts, "llvm"));
+    // Package content and native driver discovery are independent inputs to
+    // the same cache key. Start both before waiting so edits do not pay their
+    // filesystem and subprocess latency serially.
+    const [implementation, nativeEnvironment] = await Promise.all([
+      compilerImplementationIdentity(),
+      helperObjectRoute
+        ? executableLinkerEnvironmentFingerprint(
+          process.env,
+          nativeCodegenTarget()?.defaultLinker,
+        )
+        : executableNativeEnvironmentFingerprint(),
+    ]);
     earlyCacheOptions = {
       entryPath,
       outDir: opts.outDir,
@@ -737,12 +748,7 @@ async function compileTracked(
           ? resolvePlatformLinker(process.env, nativeCodegenTarget()?.defaultLinker)
           : (process.env["SCRIPTC_CC"] ?? "clang"),
       ],
-      nativeEnvironment: helperObjectRoute
-        ? await executableLinkerEnvironmentFingerprint(
-          process.env,
-          nativeCodegenTarget()?.defaultLinker,
-        )
-        : await executableNativeEnvironmentFingerprint(),
+      nativeEnvironment,
       nodeVersion: process.version,
       implementation: implementation.digest,
       implementationDependencies: implementation.dependencies,

packages/compiler/src/library/compiler-self-identity.test.ts

@@ -27,8 +27,8 @@ test("parallel fingerprinting preserves the v1 byte stream and dependency order
   const files: [string, string][] = [
     [join("a", "index.ts"), "export const value = 42;\n"],
     ["a.ts", ""],
-    ...Array.from({ length: 40 }, (_, i): [string, string] => [
-      join("z", `file${String(i).padStart(2, "0")}.js`),
+    ...Array.from({ length: 140 }, (_, i): [string, string] => [
+      join("z", `file${String(i).padStart(3, "0")}.js`),
       `// ${i}\n${"\u03bb".repeat(i * 1000)}`,
     ]),
   ];

packages/compiler/src/library/compiler-self-identity.ts

@@ -80,7 +80,7 @@ export async function compilerImplementationIdentity(
   // trips on every application edit; reading the entire package at once
   // would retain all its bytes and open an unbounded number of files.
   const hash = createHash("sha256").update("scriptc-frontend-implementation-v1\0");
-  const batchSize = 16;
+  const batchSize = 64;
   for (let start = 0; start < entries.length; start += batchSize) {
     const batch = await Promise.all(entries.slice(start, start + batchSize).map(async (entry) => {
       if (entry.directory !== undefined) return { ...entry, info: entry.directory, bytes: null };