[interop] Add support for the never type

web_generator/lib/src/ast/builtin.dart

@@ -24,11 +24,17 @@ class BuiltinType extends NamedType {
   @override
   bool isNullable;
 
+  /// This denotes a type that has a discardable result
+  ///
+  /// These are for types such as `void` or `never`
+  bool discardable;
+
   BuiltinType(
       {required this.name,
       this.typeParams = const [],
       this.fromDartJSInterop = false,
-      bool? isNullable})
+      bool? isNullable,
+      this.discardable = false})
       : isNullable = isNullable ?? false;
 
   @override
@@ -82,6 +88,11 @@ class BuiltinType extends NamedType {
       PrimitiveType.any => (isNullable ?? false)
           ? anyType
           : BuiltinType(name: 'JSAny', fromDartJSInterop: true),
+      PrimitiveType.never => BuiltinType(
+          name: 'JSAny',
+          fromDartJSInterop: true,
+          discardable: true,
+          isNullable: true),
       PrimitiveType.unknown => anyType,
       PrimitiveType.object => BuiltinType(
           name: 'JSObject', fromDartJSInterop: true, isNullable: isNullable),
@@ -185,5 +196,6 @@ enum PrimitiveType {
   undefined,
   symbol,
   array,
-  bigint
+  bigint,
+  never
 }

web_generator/lib/src/ast/declarations.dart

@@ -198,7 +198,11 @@ class VariableDeclaration extends FieldDeclaration
     if (modifier == VariableModifier.$const) {
       return Method((m) => m
         ..docs.addAll([...doc])
-        ..annotations.addAll([...annotations])
+        ..annotations.addAll([
+          ...annotations,
+          if (_checkIfDiscardable(type))
+            refer('doNotStore', 'package:meta/meta.dart')
+        ])
         ..name = name
         ..type = MethodType.getter
         ..annotations.add(generateJSAnnotation())
@@ -226,6 +230,14 @@ class VariableDeclaration extends FieldDeclaration
   }
 }
 
+bool _checkIfDiscardable(Type type) {
+  if (type case BuiltinType(discardable: final typeIsDiscardable)
+      when typeIsDiscardable) {
+    return true;
+  }
+  return false;
+}
+
 enum VariableModifier { let, $const, $var }
 
 class FunctionDeclaration extends CallableDeclaration
@@ -274,7 +286,11 @@ class FunctionDeclaration extends CallableDeclaration
 
     return Method((m) => m
       ..docs.addAll([...doc])
-      ..annotations.addAll([...annotations])
+      ..annotations.addAll([
+        ...annotations,
+        if (_checkIfDiscardable(returnType))
+          refer('doNotStore', 'package:meta/meta.dart')
+      ])
       ..external = true
       ..name = dartName ?? name
       ..annotations.add(generateJSAnnotation(
@@ -750,7 +766,11 @@ class PropertyDeclaration extends FieldDeclaration
     if (readonly) {
       return Method((m) => m
         ..docs.addAll([...doc])
-        ..annotations.addAll([...annotations])
+        ..annotations.addAll([
+          ...annotations,
+          if (_checkIfDiscardable(type))
+            refer('doNotStore', 'package:meta/meta.dart')
+        ])
         ..external = true
         ..name = dartName ?? name
         ..type = MethodType.getter
@@ -836,7 +856,11 @@ class MethodDeclaration extends CallableDeclaration
     if (isNullable) {
       return Method((m) => m
         ..docs.addAll([...doc])
-        ..annotations.addAll([...annotations])
+        ..annotations.addAll([
+          ...annotations,
+          if (_checkIfDiscardable(returnType))
+            refer('doNotStore', 'package:meta/meta.dart')
+        ])
         ..external = true
         ..name = dartName ?? name
         ..type = MethodType.getter
@@ -1015,7 +1039,11 @@ class OperatorDeclaration extends CallableDeclaration
 
     return Method((m) => m
       ..docs.addAll([...doc])
-      ..annotations.addAll([...annotations])
+      ..annotations.addAll([
+        ...annotations,
+        if (_checkIfDiscardable(returnType))
+          refer('doNotStore', 'package:meta/meta.dart')
+      ])
       ..external = true
       ..name = 'operator $name'
       ..types

web_generator/lib/src/interop_gen/transform/transformer.dart

@@ -1364,6 +1364,7 @@ class Transformer {
           TSSyntaxKind.VoidKeyword => PrimitiveType.$void,
           TSSyntaxKind.BigIntKeyword => PrimitiveType.bigint,
           TSSyntaxKind.SymbolKeyword => PrimitiveType.symbol,
+          TSSyntaxKind.NeverKeyword => PrimitiveType.never,
           _ => throw UnsupportedError(
               'The given type with kind ${type.kind} is not supported yet')
         };

web_generator/lib/src/js/typescript.types.dart

@@ -81,6 +81,7 @@ extension type const TSSyntaxKind._(num _) {
   static const TSSyntaxKind VoidKeyword = TSSyntaxKind._(116);
   static const TSSyntaxKind BigIntKeyword = TSSyntaxKind._(163);
   static const TSSyntaxKind SymbolKeyword = TSSyntaxKind._(155);
+  static const TSSyntaxKind NeverKeyword = TSSyntaxKind._(146);
 
   // types
   static const TSSyntaxKind UnionType = TSSyntaxKind._(192);

web_generator/test/integration/interop_gen/functions_expected.dart

@@ -3,6 +3,8 @@
 // ignore_for_file: no_leading_underscores_for_library_prefixes
 import 'dart:js_interop' as _i1;
 
+import 'package:meta/meta.dart' as _i2;
+
 @_i1.JS()
 external String greetUser(String name);
 @_i1.JS()
@@ -38,8 +40,12 @@ external _i1.JSObject createUser(
 ]);
 @_i1.JS()
 external T firstElement<T extends _i1.JSAny?>(_i1.JSArray<T> arr);
+@_i2.doNotStore
 @_i1.JS()
-external void throwError(String msg);
+external _i1.JSAny? throwError([String? msg]);
+@_i2.doNotStore
+@_i1.JS('throwError')
+external _i1.JSAny? throwError$1();
 @_i1.JS()
 external _i1.JSArray<T> wrapInArray<T extends _i1.JSAny?>(T value);
 @_i1.JS()

web_generator/test/integration/interop_gen/functions_input.d.ts

@@ -2,13 +2,14 @@ export declare function greetUser(name: string): string;
 export declare function logMessages(...messages: string[]): void;
 export declare function delay<U>(ms: number, returnValue?: U): Promise<U>;
 export declare function toArray(a: number): number[];
+export declare function toArray(a: string): string[];
 export declare function square(a: number): number;
 export declare function pow(a: number): number;
 export declare function pow(a: number, power: number): number;
-export declare function toArray(a: string): string[];
 export declare function createUser(name: string, age?: number, role?: string): object;
 export declare function firstElement<T>(arr: T[]): T;
-export declare function throwError(msg: string): void;
+export declare function throwError(msg?: string): never;
+export declare function throwError(): never;
 export declare function wrapInArray<T>(value: T): T[];
 export declare function identity<T = string>(value: T): T;
 export declare function someFunction<A>(arr: A[]): undefined;

web_generator/test/integration/interop_gen/variables_expected.dart

@@ -3,6 +3,8 @@
 // ignore_for_file: no_leading_underscores_for_library_prefixes
 import 'dart:js_interop' as _i1;
 
+import 'package:meta/meta.dart' as _i2;
+
 @_i1.JS()
 external double counter;
 @_i1.JS()
@@ -35,3 +37,6 @@ external _i1.JSAny? get maybeValue;
 external _i1.JSArray<_i1.JSString> get names;
 @_i1.JS()
 external _i1.JSArray<_i1.JSString> get newNames;
+@_i2.doNotStore
+@_i1.JS()
+external _i1.JSAny? get neverUseThis;

web_generator/test/integration/interop_gen/variables_input.d.ts

@@ -11,3 +11,4 @@ export declare let something: any;
 export declare const maybeValue: unknown;
 export declare const names: string[];
 export declare const newNames: Array<string>;
+export declare const neverUseThis: never;