test(dead-exports): shrink end-to-end probe to a narrow tsconfig

Author: Gustav-Simonsson

scripts/check-dead-exports.test.ts

@@ -362,12 +362,34 @@ describe("scan coverage floor", () => {
 // scripts/ tree, the real guard runs as a subprocess, and the run must exit
 // nonzero naming the probe. The probe lives only for the test (never
 // committed) so the keep-alive check cannot itself become a dead export.
+//
+// The guard normally scans the full project via ts-prune (~5s); the probe's
+// temp tsconfig includes only the probe file, so this run pays only ts-prune
+// startup while still exercising the same wired-up gate (config load,
+// allowlist validation, node-spawned ts-prune, output parsing, coverage
+// floor, exit code).
 describe("violation end to end", () => {
   test("a temp dead export fails the guard, which names it", () => {
     const probeFile = `dead-export-guard-probe-${process.pid}.ts`;
     const probeName = `deadExportGuardProbe${process.pid}`;
     const probePath = join(repoRoot, "scripts", probeFile);
+    const narrowTsconfigFile = `dead-export-guard-tsconfig-${process.pid}.json`;
+    const narrowTsconfigPath = join(repoRoot, "scripts", narrowTsconfigFile);
     writeFileSync(probePath, `export const ${probeName} = 1;\n`);
+    writeFileSync(
+      narrowTsconfigPath,
+      JSON.stringify({
+        compilerOptions: {
+          noEmit: true,
+          target: "ESNext",
+          module: "ESNext",
+          moduleResolution: "bundler",
+          skipLibCheck: true,
+        },
+        // Relative to the narrow tsconfig's own directory (scripts/).
+        files: [probeFile],
+      }),
+    );
     try {
       const ran = spawnSync(
         process.execPath,
@@ -381,6 +403,7 @@ describe("violation end to end", () => {
           env: {
             ...process.env,
             DEAD_EXPORT_GUARD_SCANNED_FILES: String(liveScannedFileCount()),
+            DEAD_EXPORT_GUARD_TSCONFIG: `scripts/${narrowTsconfigFile}`,
           },
         },
       );
@@ -390,6 +413,7 @@ describe("violation end to end", () => {
       );
     } finally {
       rmSync(probePath, { force: true });
+      rmSync(narrowTsconfigPath, { force: true });
     }
   }, 120_000);
 });

scripts/check-dead-exports.ts

@@ -25,6 +25,12 @@ import { fileURLToPath } from "node:url";
 // sets it, so the gate always computes the count in normal runs.
 const scannedFilesEnv = "DEAD_EXPORT_GUARD_SCANNED_FILES";
 
+// Test injection (same pattern as scannedFilesEnv): a subprocess test that
+// needs the wired-up gate without paying for the ~5s full-project ts-prune
+// run can point the pinned scan at a smaller tsconfig. Production never sets
+// it, so the gate always scans the pinned tsconfig in normal runs.
+const tsconfigEnv = "DEAD_EXPORT_GUARD_TSCONFIG";
+
 const here = dirname(fileURLToPath(import.meta.url));
 const repoRoot = dirname(here);
 const allowlistPath = join(here, "dead-export-allowlist.txt");
@@ -351,6 +357,19 @@ function main(): void {
   } catch (err) {
     fail(`dead-export guard: invalid guard config: ${(err as Error).message}`);
   }
+  const overrideTsconfig = process.env[tsconfigEnv];
+  if (overrideTsconfig !== undefined) {
+    if (!existsSync(join(repoRoot, overrideTsconfig))) {
+      fail(
+        `dead-export guard: tsconfig override not found: ${overrideTsconfig}`,
+      );
+    }
+    config = {
+      ...config,
+      tsconfig: overrideTsconfig,
+      tsPruneArgs: ["-p", overrideTsconfig],
+    };
+  }
   const allowlistText = readFileSync(allowlistPath, "utf8");
   const allowlistProblems = [
     ...validateAllowlistText(allowlistText),

scripts/ci-timings.json

@@ -1,7 +1,7 @@
 {
   "version": 1,
   "files": {
-    "scripts/check-dead-exports.test.ts": 6178,
+    "scripts/check-dead-exports.test.ts": 1769,
     "scripts/test-parallel.test.ts": 2496,
     "src/plugins/shell-guard-plugin.test.ts": 1883,
     "src/tui/tool-execution-watchdog.test.ts": 1853,