Implement Generator Function Constructor (#2174)

This Pull Request changes the following:

- Modify `CreateDynamicFunction` to work with generator functions.
- Add the name `anonymus` to functions created via `CreateDynamicFunction` to comply with the spec. 
- Fix a bug in the `Yield` parser where the parser would expect a token when no token is a legal case.
- Change the `Yield::new` function to require less turbofishes.

boa_engine/src/builtins/async_function/mod.rs

@@ -100,7 +100,7 @@ impl AsyncFunction {
         context: &mut Context,
     ) -> JsResult<JsValue> {
         crate::builtins::function::BuiltInFunctionObject::create_dynamic_function(
-            new_target, args, true, context,
+            new_target, args, true, false, context,
         )
         .map(Into::into)
     }

boa_engine/src/builtins/function/mod.rs

@@ -460,7 +460,7 @@ impl BuiltInFunctionObject {
         args: &[JsValue],
         context: &mut Context,
     ) -> JsResult<JsValue> {
-        Self::create_dynamic_function(new_target, args, false, context).map(Into::into)
+        Self::create_dynamic_function(new_target, args, false, false, context).map(Into::into)
     }
 
     /// `CreateDynamicFunction ( constructor, newTarget, kind, args )`
@@ -473,40 +473,56 @@ impl BuiltInFunctionObject {
         new_target: &JsValue,
         args: &[JsValue],
         r#async: bool,
+        generator: bool,
         context: &mut Context,
     ) -> JsResult<JsObject> {
-        let prototype =
-            get_prototype_from_constructor(new_target, StandardConstructors::function, context)?;
+        let default = if r#async {
+            StandardConstructors::async_function
+        } else if generator {
+            StandardConstructors::generator_function
+        } else {
+            StandardConstructors::function
+        };
+
+        let prototype = get_prototype_from_constructor(new_target, default, context)?;
         if let Some((body_arg, args)) = args.split_last() {
-            let parameters =
-                if args.is_empty() {
-                    FormalParameterList::empty()
-                } else {
-                    let mut parameters = Vec::with_capacity(args.len());
-                    for arg in args {
-                        parameters.push(arg.to_string(context)?);
+            let parameters = if args.is_empty() {
+                FormalParameterList::empty()
+            } else {
+                let mut parameters = Vec::with_capacity(args.len());
+                for arg in args {
+                    parameters.push(arg.to_string(context)?);
+                }
+                let mut parameters = parameters.join(",");
+                parameters.push(')');
+
+                let parameters = match Parser::new(parameters.as_bytes()).parse_formal_parameters(
+                    context.interner_mut(),
+                    generator,
+                    r#async,
+                ) {
+                    Ok(parameters) => parameters,
+                    Err(e) => {
+                        return context.throw_syntax_error(format!(
+                            "failed to parse function parameters: {e}"
+                        ))
                     }
-                    let mut parameters = parameters.join(",");
-                    parameters.push(')');
-
-                    let parameters = match Parser::new(parameters.as_bytes())
-                        .parse_formal_parameters(context.interner_mut(), false, r#async)
-                    {
-                        Ok(parameters) => parameters,
-                        Err(e) => {
-                            return context.throw_syntax_error(format!(
-                                "failed to parse function parameters: {e}"
-                            ))
-                        }
-                    };
-                    parameters
                 };
 
+                if generator && parameters.contains_yield_expression() {
+                    return context.throw_syntax_error(
+                            "yield expression is not allowed in formal parameter list of generator function",
+                        );
+                }
+
+                parameters
+            };
+
             let body_arg = body_arg.to_string(context)?;
 
             let body = match Parser::new(body_arg.as_bytes()).parse_function_body(
                 context.interner_mut(),
-                false,
+                generator,
                 r#async,
             ) {
                 Ok(statement_list) => statement_list,
@@ -567,23 +583,45 @@ impl BuiltInFunctionObject {
 
             let code = crate::bytecompiler::ByteCompiler::compile_function_code(
                 crate::bytecompiler::FunctionKind::Expression,
-                Some(Sym::EMPTY_STRING),
+                Some(Sym::ANONYMOUS),
                 &parameters,
                 &body,
+                generator,
                 false,
+                context,
+            )?;
+
+            let environments = context.realm.environments.pop_to_global();
+
+            let function_object = if generator {
+                crate::vm::create_generator_function_object(code, context)
+            } else {
+                crate::vm::create_function_object(code, r#async, Some(prototype), context)
+            };
+
+            context.realm.environments.extend(environments);
+
+            Ok(function_object)
+        } else if generator {
+            let code = crate::bytecompiler::ByteCompiler::compile_function_code(
+                crate::bytecompiler::FunctionKind::Expression,
+                Some(Sym::ANONYMOUS),
+                &FormalParameterList::empty(),
+                &StatementList::default(),
+                true,
                 false,
                 context,
             )?;
 
             let environments = context.realm.environments.pop_to_global();
-            let function_object = crate::vm::create_function_object(code, r#async, context);
+            let function_object = crate::vm::create_generator_function_object(code, context);
             context.realm.environments.extend(environments);
 
             Ok(function_object)
-        } else if r#async {
+        } else {
             let code = crate::bytecompiler::ByteCompiler::compile_function_code(
                 crate::bytecompiler::FunctionKind::Expression,
-                Some(Sym::EMPTY_STRING),
+                Some(Sym::ANONYMOUS),
                 &FormalParameterList::empty(),
                 &StatementList::default(),
                 false,
@@ -592,20 +630,11 @@ impl BuiltInFunctionObject {
             )?;
 
             let environments = context.realm.environments.pop_to_global();
-            let function_object = crate::vm::create_function_object(code, r#async, context);
+            let function_object =
+                crate::vm::create_function_object(code, r#async, Some(prototype), context);
             context.realm.environments.extend(environments);
 
             Ok(function_object)
-        } else {
-            let this = JsObject::from_proto_and_data(
-                prototype,
-                ObjectData::function(Function::Native {
-                    function: |_, _, _| Ok(JsValue::undefined()),
-                    constructor: Some(ConstructorKind::Base),
-                }),
-            );
-
-            Ok(this)
         }
     }
 

boa_engine/src/builtins/generator_function/mod.rs

@@ -11,18 +11,18 @@
 //! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/GeneratorFunction
 
 use crate::{
-    builtins::{function::Function, BuiltIn},
-    context::intrinsics::StandardConstructors,
-    object::{internal_methods::get_prototype_from_constructor, JsObject, ObjectData},
+    builtins::{
+        function::{BuiltInFunctionObject, ConstructorKind, Function},
+        BuiltIn,
+    },
+    object::ObjectData,
     property::PropertyDescriptor,
     symbol::WellKnownSymbols,
     value::JsValue,
     Context, JsResult,
 };
 use boa_profiler::Profiler;
 
-use super::function::ConstructorKind;
-
 /// The internal representation on a `Generator` object.
 #[derive(Debug, Clone, Copy)]
 pub struct GeneratorFunction;
@@ -111,25 +111,18 @@ impl BuiltIn for GeneratorFunction {
 }
 
 impl GeneratorFunction {
+    /// `GeneratorFunction ( p1, p2, … , pn, body )`
+    ///
+    /// More information:
+    ///  - [ECMAScript reference][spec]
+    ///
+    /// [spec]: https://tc39.es/ecma262/#sec-generatorfunction
     pub(crate) fn constructor(
         new_target: &JsValue,
-        _: &[JsValue],
+        args: &[JsValue],
         context: &mut Context,
     ) -> JsResult<JsValue> {
-        let prototype = get_prototype_from_constructor(
-            new_target,
-            StandardConstructors::generator_function,
-            context,
-        )?;
-
-        let this = JsObject::from_proto_and_data(
-            prototype,
-            ObjectData::function(Function::Native {
-                function: |_, _, _| Ok(JsValue::undefined()),
-                constructor: Some(ConstructorKind::Base),
-            }),
-        );
-
-        Ok(this.into())
+        BuiltInFunctionObject::create_dynamic_function(new_target, args, false, true, context)
+            .map(Into::into)
     }
 }

boa_engine/src/syntax/ast/node/yield/mod.rs

@@ -29,13 +29,12 @@ impl Yield {
     }
 
     /// Creates a `Yield` AST node.
-    pub fn new<E, OE>(expr: OE, delegate: bool) -> Self
+    pub fn new<E>(expr: Option<E>, delegate: bool) -> Self
     where
         E: Into<Node>,
-        OE: Into<Option<E>>,
     {
         Self {
-            expr: expr.into().map(E::into).map(Box::new),
+            expr: expr.map(Into::into).map(Box::new),
             delegate,
         }
     }

boa_engine/src/syntax/parser/expression/assignment/yield.rs

@@ -14,7 +14,7 @@ use crate::syntax::{
         Keyword, Punctuator,
     },
     lexer::TokenKind,
-    parser::{AllowAwait, AllowIn, Cursor, ParseError, ParseResult, TokenParser},
+    parser::{AllowAwait, AllowIn, Cursor, ParseResult, TokenParser},
 };
 use boa_interner::Interner;
 use boa_profiler::Profiler;
@@ -63,16 +63,18 @@ where
             interner,
         )?;
 
-        let token = cursor.peek(0, interner)?.ok_or(ParseError::AbruptEnd)?;
+        let token = if let Some(token) = cursor.peek(0, interner)? {
+            token
+        } else {
+            return Ok(Node::Yield(Yield::new::<Node>(None, false)));
+        };
+
         match token.kind() {
             TokenKind::Punctuator(Punctuator::Mul) => {
                 cursor.next(interner)?.expect("token disappeared");
                 let expr = AssignmentExpression::new(None, self.allow_in, true, self.allow_await)
                     .parse(cursor, interner)?;
-                Ok(Node::Yield(Yield::new::<Node, Option<Node>>(
-                    Some(expr),
-                    true,
-                )))
+                Ok(Node::Yield(Yield::new(Some(expr), true)))
             }
             TokenKind::Identifier(_)
             | TokenKind::Punctuator(
@@ -109,12 +111,9 @@ where
             | TokenKind::TemplateMiddle(_) => {
                 let expr = AssignmentExpression::new(None, self.allow_in, true, self.allow_await)
                     .parse(cursor, interner)?;
-                Ok(Node::Yield(Yield::new::<Node, Option<Node>>(
-                    Some(expr),
-                    false,
-                )))
+                Ok(Node::Yield(Yield::new(Some(expr), false)))
             }
-            _ => Ok(Node::Yield(Yield::new::<Node, Option<Node>>(None, false))),
+            _ => Ok(Node::Yield(Yield::new::<Node>(None, false))),
         }
     }
 }

boa_engine/src/syntax/parser/expression/primary/generator_expression/tests.rs

@@ -25,7 +25,7 @@ fn check_generator_function_expression() {
                     GeneratorExpr::new::<_, _, StatementList>(
                         Some(gen),
                         FormalParameterList::default(),
-                        vec![Yield::new(Const::from(1), false).into()].into(),
+                        vec![Yield::new(Some(Const::from(1)), false).into()].into(),
                     )
                     .into(),
                 ),
@@ -53,7 +53,7 @@ fn check_generator_function_delegate_yield_expression() {
                     GeneratorExpr::new::<_, _, StatementList>(
                         Some(gen),
                         FormalParameterList::default(),
-                        vec![Yield::new(Const::from(1), true).into()].into(),
+                        vec![Yield::new(Some(Const::from(1)), true).into()].into(),
                     )
                     .into(),
                 ),

boa_engine/src/vm/code_block.rs

@@ -446,11 +446,14 @@ impl ToInternedString for CodeBlock {
 pub(crate) fn create_function_object(
     code: Gc<CodeBlock>,
     r#async: bool,
+    prototype: Option<JsObject>,
     context: &mut Context,
 ) -> JsObject {
     let _timer = Profiler::global().start_event("JsVmFunction::new", "vm");
 
-    let function_prototype = if r#async {
+    let function_prototype = if let Some(prototype) = prototype {
+        prototype
+    } else if r#async {
         context
             .intrinsics()
             .constructors()

boa_engine/src/vm/mod.rs

@@ -14,7 +14,7 @@ use crate::{
     value::Numeric,
     vm::{
         call_frame::CatchAddresses,
-        code_block::{create_generator_function_object, initialize_instance_elements, Readable},
+        code_block::{initialize_instance_elements, Readable},
     },
     Context, JsBigInt, JsResult, JsString, JsValue,
 };
@@ -30,7 +30,7 @@ pub use {call_frame::CallFrame, code_block::CodeBlock, opcode::Opcode};
 
 pub(crate) use {
     call_frame::{FinallyReturn, GeneratorResumeKind, TryStackEntry},
-    code_block::create_function_object,
+    code_block::{create_function_object, create_generator_function_object},
     opcode::BindingOpcode,
 };
 
@@ -1683,13 +1683,13 @@ impl Context {
             Opcode::GetFunction => {
                 let index = self.vm.read::<u32>();
                 let code = self.vm.frame().code.functions[index as usize].clone();
-                let function = create_function_object(code, false, self);
+                let function = create_function_object(code, false, None, self);
                 self.vm.push(function);
             }
             Opcode::GetFunctionAsync => {
                 let index = self.vm.read::<u32>();
                 let code = self.vm.frame().code.functions[index as usize].clone();
-                let function = create_function_object(code, true, self);
+                let function = create_function_object(code, true, None, self);
                 self.vm.push(function);
             }
             Opcode::GetGenerator => {

boa_interner/src/sym.rs

@@ -82,6 +82,9 @@ impl Sym {
     /// Symbol for the `"public"` string.
     pub const PUBLIC: Self = unsafe { Self::new_unchecked(22) };
 
+    /// Symbol for the `"anonymous"` string.
+    pub const ANONYMOUS: Self = unsafe { Self::new_unchecked(23) };
+
     /// Creates a new [`Sym`] from the provided `value`, or returns `None` if `index` is zero.
     #[inline]
     pub(super) fn new(value: usize) -> Option<Self> {
@@ -141,6 +144,7 @@ pub(super) static COMMON_STRINGS: phf::OrderedSet<&'static str> = {
         "private",
         "protected",
         "public",
+        "anonymous",
     };
     // A `COMMON_STRINGS` of size `usize::MAX` would cause an overflow on our `Interner`
     sa::const_assert!(COMMON_STRINGS.len() < usize::MAX);