wasm: correctly return from run() in wasm_exec.js

Instead of hanging forever, it should return the exit code from os.Exit.

main_test.go

@@ -766,12 +766,56 @@ func TestWasmExportJS(t *testing.T) {
 	}
 }
 
+// Test whether Go.run() (in wasm_exec.js) normally returns and returns the
+// right exit code.
+func TestWasmExit(t *testing.T) {
+	t.Parallel()
+
+	type testCase struct {
+		name   string
+		output string
+	}
+
+	tests := []testCase{
+		{name: "normal", output: "exit code: 0\n"},
+		{name: "exit-0", output: "exit code: 0\n"},
+		{name: "exit-0-sleep", output: "slept\nexit code: 0\n"},
+		{name: "exit-1", output: "exit code: 1\n"},
+		{name: "exit-1-sleep", output: "slept\nexit code: 1\n"},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			options := optionsFromTarget("wasm", sema)
+			buildConfig, err := builder.NewConfig(&options)
+			if err != nil {
+				t.Fatal(err)
+			}
+			buildConfig.Target.Emulator = "node testdata/wasmexit.js {}"
+			output := &bytes.Buffer{}
+			_, err = buildAndRun("testdata/wasmexit.go", buildConfig, output, []string{tc.name}, nil, time.Minute, func(cmd *exec.Cmd, result builder.BuildResult) error {
+				return cmd.Run()
+			})
+			if err != nil {
+				t.Error(err)
+			}
+			expected := "wasmexit test: " + tc.name + "\n" + tc.output
+			checkOutputData(t, []byte(expected), output.Bytes())
+		})
+	}
+}
+
 // Check whether the output of a test equals the expected output.
 func checkOutput(t *testing.T, filename string, actual []byte) {
 	expectedOutput, err := os.ReadFile(filename)
 	if err != nil {
 		t.Fatal("could not read output file:", err)
 	}
+	checkOutputData(t, expectedOutput, actual)
+}
+
+func checkOutputData(t *testing.T, expectedOutput, actual []byte) {
 	expectedOutput = bytes.ReplaceAll(expectedOutput, []byte("\r\n"), []byte("\n"))
 	actual = bytes.ReplaceAll(actual, []byte("\r\n"), []byte("\n"))
 

src/runtime/runtime_tinygowasm.go

@@ -80,12 +80,17 @@ func abort() {
 
 //go:linkname syscall_Exit syscall.Exit
 func syscall_Exit(code int) {
-	// TODO: should we call __stdio_exit here?
-	// It's a low-level exit (syscall.Exit) so doing any libc stuff seems
-	// unexpected, but then where else should stdio buffers be flushed?
+	// Flush stdio buffers.
+	__stdio_exit()
+
+	// Exit the program.
 	proc_exit(uint32(code))
 }
 
+func mainReturnExit() {
+	syscall_Exit(0)
+}
+
 // TinyGo does not yet support any form of parallelism on WebAssembly, so these
 // can be left empty.
 

src/runtime/runtime_tinygowasm_unknown.go

@@ -31,6 +31,10 @@ func abort() {
 
 //go:linkname syscall_Exit syscall.Exit
 func syscall_Exit(code int) {
+	// Because this is the "unknown" target we can't call an exit function.
+	// But we also can't just return since the program will likely expect this
+	// function to never return. So we panic instead.
+	runtimePanic("unsupported: syscall.Exit")
 }
 
 // There is not yet any support for any form of parallelism on WebAssembly, so these

src/runtime/runtime_tinygowasmp2.go

@@ -60,6 +60,13 @@ func syscall_Exit(code int) {
 	exit.Exit(code != 0)
 }
 
+func mainReturnExit() {
+	// WASIp2 does not use _start, instead it uses _initialize and a custom
+	// WASIp2-specific main function. So this should never be called in
+	// practice.
+	runtimePanic("unreachable: _start was called")
+}
+
 // TinyGo does not yet support any form of parallelism on WebAssembly, so these
 // can be left empty.
 

src/runtime/runtime_wasip1.go

@@ -91,10 +91,6 @@ func ticks() timeUnit {
 	return timeUnit(nano)
 }
 
-func beforeExit() {
-	__stdio_exit()
-}
-
 // Implementations of WASI APIs
 
 //go:wasmimport wasi_snapshot_preview1 args_get

src/runtime/runtime_wasip2.go

@@ -52,6 +52,3 @@ func sleepTicks(d timeUnit) {
 func ticks() timeUnit {
 	return timeUnit(monotonicclock.Now())
 }
-
-func beforeExit() {
-}

src/runtime/runtime_wasm_js.go

@@ -32,7 +32,3 @@ func sleepTicks(d timeUnit)
 
 //go:wasmimport gojs runtime.ticks
 func ticks() timeUnit
-
-func beforeExit() {
-	__stdio_exit()
-}

src/runtime/runtime_wasm_unknown.go

@@ -34,5 +34,8 @@ func ticks() timeUnit {
 	return timeUnit(0)
 }
 
-func beforeExit() {
+func mainReturnExit() {
+	// Don't exit explicitly here. We can't (there is no environment with an
+	// exit call) but also it's not needed. We can just let _start and main.main
+	// return to the caller.
 }

src/runtime/runtime_wasmentry.go

@@ -19,7 +19,8 @@ func wasmEntryCommand() {
 	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
 	run()
 	if mainExited {
-		beforeExit()
+		// To make sure wasm_exec.js knows that we've exited, exit explicitly.
+		mainReturnExit()
 	}
 }
 

targets/wasm_exec.js

@@ -132,6 +132,7 @@
 	const decoder = new TextDecoder("utf-8");
 	let reinterpretBuf = new DataView(new ArrayBuffer(8));
 	var logLine = [];
+	const wasmExit = {}; // thrown to exit via proc_exit (not an error)
 
 	global.Go = class {
 		constructor() {
@@ -270,14 +271,11 @@
 					fd_close: () => 0,      // dummy
 					fd_fdstat_get: () => 0, // dummy
 					fd_seek: () => 0,       // dummy
-					"proc_exit": (code) => {
-						if (global.process) {
-							// Node.js
-							process.exit(code);
-						} else {
-							// Can't exit in a browser.
-							throw 'trying to exit with code ' + code;
-						}
+					proc_exit: (code) => {
+						this.exited = true;
+						this.exitCode = code;
+						this._resolveExitPromise();
+						throw wasmExit;
 					},
 					random_get: (bufPtr, bufLen) => {
 						crypto.getRandomValues(loadSlice(bufPtr, bufLen));
@@ -293,7 +291,14 @@
 					// func sleepTicks(timeout float64)
 					"runtime.sleepTicks": (timeout) => {
 						// Do not sleep, only reactivate scheduler after the given timeout.
-						setTimeout(this._inst.exports.go_scheduler, timeout);
+						setTimeout(() => {
+							if (this.exited) return;
+							try {
+								this._inst.exports.go_scheduler();
+							} catch (e) {
+								if (e !== wasmExit) throw e;
+							}
+						}, timeout);
 					},
 
 					// func finalizeRef(v ref)
@@ -465,12 +470,23 @@
 			this._ids = new Map();  // mapping from JS values to reference ids
 			this._idPool = [];      // unused ids that have been garbage collected
 			this.exited = false;    // whether the Go program has exited
+			this.exitCode = 0;
 
 			if (this._inst.exports._start) {
-				this._inst.exports._start();
+				let exitPromise = new Promise((resolve, reject) => {
+					this._resolveExitPromise = resolve;
+				});
+
+				// Run program, but catch the wasmExit exception that's thrown
+				// to return back here.
+				try {
+					this._inst.exports._start();
+				} catch (e) {
+					if (e !== wasmExit) throw e;
+				}
 
-				// TODO: wait until the program exists.
-				await new Promise(() => {});
+				await exitPromise;
+				return this.exitCode;
 			} else {
 				this._inst.exports._initialize();
 			}
@@ -480,7 +496,11 @@
 			if (this.exited) {
 				throw new Error("Go program has already exited");
 			}
-			this._inst.exports.resume();
+			try {
+				this._inst.exports.resume();
+			} catch (e) {
+				if (e !== wasmExit) throw e;
+			}
 			if (this.exited) {
 				this._resolveExitPromise();
 			}