Let completion output drain before exit

src/cli.ts

@@ -1672,7 +1672,8 @@ async function main(): Promise<void> {
     case "completions": {
       // `pty completions <shell>` — print a fish/bash/zsh completion script.
       const { cmdCompletions } = await import("./completions.ts");
-      process.exit(cmdCompletions(args.slice(1)));
+      process.exitCode = cmdCompletions(args.slice(1));
+      return;
     }
 
     case "version":

tests/completions.test.ts

@@ -13,7 +13,7 @@ import { describe, it, expect } from "vitest";
 import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
-import { fileURLToPath } from "node:url";
+import { fileURLToPath, pathToFileURL } from "node:url";
 import { spawnSync } from "node:child_process";
 import { execSync } from "node:child_process";
 import { COMMANDS } from "../src/completions.ts";
@@ -186,6 +186,26 @@ printf '%s\n' "\${COMPREPLY[@]}"`;
     }
   });
 
+  it("lets piped stdout drain before exiting", () => {
+    const delayedStdout = pathToFileURL(
+      path.join(__dirname, "fixtures", "delayed-stdout.mjs"),
+    ).href;
+    for (const shell of ["fish", "bash", "zsh"]) {
+      const r = spawnSync(
+        nodeBin,
+        ["--import", delayedStdout, cliPath, "completions", shell],
+        { encoding: "utf8" },
+      );
+      const checkedIn = fs.readFileSync(
+        path.join(__dirname, "..", "completions", `pty.${shell}`),
+        "utf8",
+      );
+
+      expect(r.status, r.stderr).toBe(0);
+      expect(r.stdout, `${shell} output was truncated`).toBe(checkedIn);
+    }
+  });
+
   it("prints usage and exits non-zero for an unknown shell", () => {
     const r = spawnSync(nodeBin, [cliPath, "completions", "tcsh"], {
       encoding: "utf8",

tests/fixtures/delayed-stdout.mjs

@@ -0,0 +1,10 @@
+// The natural race depends on the Node version, operating system, and pipe
+// scheduling, so it does not reproduce on every supported setup. Delay the
+// write so a forced exit loses the text on every platform, independent of
+// pipe size or scheduling luck.
+const write = process.stdout.write.bind(process.stdout);
+
+process.stdout.write = (chunk, encoding, callback) => {
+  setTimeout(() => write(chunk, encoding, callback), 25);
+  return false;
+};