feat(runtime): add PanicNilError and register runtime.Error

gs/builtin/panic.ts

@@ -51,6 +51,9 @@ export class RuntimeError extends Error {
   Error(): string {
     return this.message
   }
+
+  // RuntimeError marks the value as a runtime.Error, as in Go.
+  RuntimeError(): void {}
 }
 
 /**

gs/runtime/runtime.ts

@@ -407,6 +407,17 @@ export interface Error {
   Error(): string | PromiseLike<string>
 }
 
+// Error is registered with the runtime type system, so type assertions to
+// runtime.Error see its methods.
+$.registerInterfaceType('runtime.Error', null, [
+  {
+    name: 'Error',
+    args: [],
+    returns: [{ type: { kind: $.TypeKind.Basic, name: 'string' } }],
+  },
+  { name: 'RuntimeError', args: [], returns: [] },
+])
+
 // TypeAssertionError represents a failed type assertion.
 export class TypeAssertionError implements Error {
   constructor(
@@ -424,6 +435,31 @@ export class TypeAssertionError implements Error {
   }
 }
 
+// PanicNilError is the value of a panic called with a nil argument, as Go
+// 1.21 and later panic with.
+export class PanicNilError {
+  constructor(_init?: Partial<{}>) {}
+
+  public clone(): PanicNilError {
+    return new PanicNilError()
+  }
+
+  public Error(): string {
+    return 'runtime error: panic called with nil argument'
+  }
+
+  public RuntimeError(): void {}
+
+  // PanicNilError is registered with the runtime type system; the compiler
+  // gives its method signatures, for reflection.
+  static __typeInfo = $.registerStructType(
+    'runtime.PanicNilError',
+    new PanicNilError(),
+    [],
+    PanicNilError,
+  )
+}
+
 // PanicError represents a panic.
 export class PanicError implements Error {
   constructor(public readonly value: any) {}

gs/runtime/stubs.gs.ts

@@ -46,14 +46,6 @@ export function MutexProfile(..._args: any[]): any {
   return $.notImplemented("runtime.MutexProfile")
 }
 
-export class PanicNilError {
-  [field: string]: any
-
-  constructor(..._args: any[]) {
-    $.notImplemented("runtime.PanicNilError")
-  }
-}
-
 export class Pinner {
   [field: string]: any
 

tests/tests/package_import_runtime/expected.log

@@ -21,3 +21,5 @@ Cleanup stopped
 Finalizer ignored
 locked goroutine ran
 main unlocked
+PanicNilError: runtime error: panic called with nil argument true
+recovered runtime.Error: true

tests/tests/package_import_runtime/package_import_runtime.go

@@ -58,6 +58,7 @@ func main() {
 	println("Finalizer ignored")
 
 	lockOSThread()
+	panicNilError()
 }
 
 // callers reports frames of its own stack and names a function value.
@@ -124,3 +125,18 @@ func lockOSThread() {
 	runtime.UnlockOSThread()
 	println("main unlocked")
 }
+
+// panicNilError checks the value Go panics with for panic(nil).
+func panicNilError() {
+	var err error = &runtime.PanicNilError{}
+	_, isRuntime := err.(runtime.Error)
+	println("PanicNilError:", err.Error(), isRuntime)
+
+	defer func() {
+		_, ok := recover().(runtime.Error)
+		println("recovered runtime.Error:", ok)
+	}()
+	var s []int
+	i := 5
+	_ = s[i]
+}

tests/tests/package_import_runtime/package_import_runtime.gs.ts

@@ -125,6 +125,7 @@ export async function main(): globalThis.Promise<void> {
 	await $.println("Finalizer ignored")
 
 	await lockOSThread()
+	await panicNilError()
 }
 
 export async function callers(): globalThis.Promise<void> {
@@ -178,6 +179,29 @@ export async function lockOSThread(): globalThis.Promise<void> {
 	await $.println("main unlocked")
 }
 
+export async function panicNilError(): globalThis.Promise<void> {
+	const __defer = new $.AsyncDisposableStack()
+	try {
+		let err: $.GoError = $.interfaceValue<$.GoError>(new runtime.PanicNilError(), "*runtime.PanicNilError", __goscriptStatic2())
+		let [, isRuntime] = $.typeAssertTuple<runtime.Error | null>(err, "runtime.Error")
+		await $.println("PanicNilError:", (__goscriptAwait = (err !== null && (err as any).__isVarRef !== true && ((err as any).__goValue === undefined || (err as any).__goType?.charCodeAt(0) !== 42) ? (err as Exclude<$.GoError, null>) : $.pointerValue<Exclude<$.GoError, null>>(err)).Error(), __goscriptAwait instanceof Promise ? await __goscriptAwait : __goscriptAwait), isRuntime)
+
+		__defer.defer(async () => { await (async () => {
+			let [, ok] = $.typeAssertTuple<runtime.Error | null>($.recover(), "runtime.Error")
+			await $.println("recovered runtime.Error:", ok)
+		})() })
+		let s: $.Slice<number> = null! as $.Slice<number>
+		let i = 5
+		$.arrayIndex(s!, i)
+		await __defer.dispose()
+	} catch (e) {
+		await __defer.disposePanic(e)
+		if (!$.recovered(e)) {
+			throw e
+		}
+	}
+}
+
 var __goscriptStatic0$value: any
 function __goscriptStatic0(): any {
 	return __goscriptStatic0$value ??= ({[$.genericTypeArgsMarker]: $.genericTypeArgsBrand, E: { type: /* @__PURE__ */ $.basicType("int"), zero: () => 0 }})
@@ -188,6 +212,13 @@ function __goscriptStatic1(): any {
 	return __goscriptStatic1$value ??= ([{Get: (receiver: any) => $.pointerValue(receiver).Get(__goscriptStatic0())}, [$.methodSignature("Get", [], [/* @__PURE__ */ $.basicType("int")], true, false)]])
 }
 
+var __goscriptStatic2$value: any
+function __goscriptStatic2(): any {
+	return __goscriptStatic2$value ??= ($.overrideTypeMethods(/* @__PURE__ */ $.pointerType("runtime.PanicNilError"), "runtime.PanicNilError", () => [$.methodSignature("Error", [], [/* @__PURE__ */ $.basicType("string")], true), $.methodSignature("RuntimeError", [], [], true)]))
+}
+
+var __goscriptAwait: any
+
 __goscriptInit0()
 
 if ($.isMainScript(import.meta)) {