Fix WASI LSP shutdown

Return io.EOF when WASI stdin closes instead of triggering repeated
empty reads. Cover the command lifecycle in the unified module test.

Author: jakebailey

packages/typescript/test/browser/suite.test.ts

@@ -50,7 +50,7 @@ const fileExclusions = [
     {
         mode: "sync",
         file: "sync/wasm.test.ts",
-        tests: 2,
+        tests: 3,
         reason: "These Node.js integration tests use node:fs and node:wasi; wasm.test.ts covers browser API loading.",
     },
 ] as const;

packages/typescript/test/sync/wasm.test.ts

@@ -56,6 +56,39 @@ describe("API over WebAssembly", () => {
         }
     });
 
+    test("exits successfully when LSP stdin closes", async () => {
+        const WebAssembly = (globalThis as any).WebAssembly;
+        const directory = await mkdtemp(path.join(tmpdir(), "typescript-wasip1-"));
+        try {
+            const stdin = await open(path.join(directory, "stdin"), "w+");
+            const stdout = await open(path.join(directory, "stdout"), "w+");
+            const stderr = await open(path.join(directory, "stderr"), "w+");
+            try {
+                const wasi = new WASI({
+                    version: "preview1",
+                    args: ["tsc.wasm", "--lsp", "--stdio"],
+                    env: { PWD: "/" },
+                    preopens: { "/": process.cwd() },
+                    stdin: stdin.fd,
+                    stdout: stdout.fd,
+                    stderr: stderr.fd,
+                    returnOnExit: true,
+                });
+                const module = await WebAssembly.compile(await readFile(wasmURL));
+                const instance = await WebAssembly.instantiate(module, {
+                    wasi_snapshot_preview1: wasi.wasiImport,
+                });
+                assert.strictEqual(wasi.start(instance), 0);
+            }
+            finally {
+                await Promise.all([stdin.close(), stdout.close(), stderr.close()]);
+            }
+        }
+        finally {
+            await rm(directory, { recursive: true });
+        }
+    });
+
     test("runs the compiler and checker through the reactor", async () => {
         const WebAssembly = (globalThis as any).WebAssembly;
         const module = await WebAssembly.compile(

tsc/cmd/tsc/lsp_stdin_wasip1.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"io"
 	"runtime"
 	"syscall"
 )
@@ -12,6 +13,9 @@ type wasiStdin struct{}
 func (wasiStdin) Read(buffer []byte) (int, error) {
 	for {
 		n, err := syscall.Read(syscall.Stdin, buffer)
+		if n == 0 && err == nil {
+			return 0, io.EOF
+		}
 		if err != syscall.EAGAIN {
 			return n, err
 		}