feat: add syntax for explicitly specifying closure types

Author: alexvitkov

crates/nargo_cli/tests/execution_success/closure_explicit_types/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "closure_explicit_types"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/execution_success/closure_explicit_types/src/main.nr

@@ -0,0 +1,60 @@
+
+fn ret_normal_lambda1() -> fn() -> Field {
+    || 10
+}
+
+// explicitly specified empty capture group
+fn ret_normal_lambda2() -> fn[]() -> Field {
+    || 20
+}
+
+// return lamda that captures a thing
+fn ret_closure1() -> fn[Field]() -> Field {
+    let x = 20;
+    || x + 10
+}
+
+// return lamda that captures two things
+fn ret_closure2() -> fn[Field,Field]() -> Field {
+    let x = 20;
+    let y = 10;
+    || x + y + 10
+}
+
+// return lamda that captures two things with different types
+fn ret_closure3() -> fn[u32,u64]() -> u64 {
+    let x: u32 = 20;
+    let y: u64 = 10;
+    || x as u64 + y + 10
+}
+
+// accepts closure that has 1 thing in its env, calls it and returns the result
+fn accepts_closure1(f: fn[Field]() -> Field) -> Field {
+    f()
+}
+
+// accepts closure that has 1 thing in its env and returns it
+fn accepts_closure2(f: fn[Field]() -> Field) -> fn[Field]() -> Field {
+    f
+}
+
+// accepts closure with different types in the capture group
+fn accepts_closure3(f: fn[u32, u64]() -> u64) -> u64 {
+    f()
+}
+
+fn main() {
+    assert(ret_normal_lambda1()() == 10);
+    assert(ret_normal_lambda2()() == 20);
+    assert(ret_closure1()() == 30);
+    assert(ret_closure2()() == 40);
+    assert(ret_closure3()() == 40);
+
+    let x = 50;
+    assert(accepts_closure1(|| x) == 50);
+    assert(accepts_closure2(|| x + 10)() == 60);
+
+    let y: u32 = 30;
+    let z: u64 = 40;
+    assert(accepts_closure3(|| y as u64 + z) == 70);
+}

crates/noirc_frontend/src/ast/mod.rs

@@ -50,7 +50,11 @@ pub enum UnresolvedType {
     // Note: Tuples have no visibility, instead each of their elements may have one.
     Tuple(Vec<UnresolvedType>),
 
-    Function(/*args:*/ Vec<UnresolvedType>, /*ret:*/ Box<UnresolvedType>),
+    Function(
+        /*args:*/ Vec<UnresolvedType>,
+        /*ret:*/ Box<UnresolvedType>,
+        /*env:*/ Box<UnresolvedType>,
+    ),
 
     Unspecified, // This is for when the user declares a variable without specifying it's type
     Error,
@@ -109,9 +113,19 @@ impl std::fmt::Display for UnresolvedType {
                 Some(len) => write!(f, "str<{len}>"),
             },
             FormatString(len, elements) => write!(f, "fmt<{len}, {elements}"),
-            Function(args, ret) => {
+            Function(args, ret, env) => {
                 let args = vecmap(args, ToString::to_string);
-                write!(f, "fn({}) -> {ret}", args.join(", "))
+
+                match &**env {
+                    UnresolvedType::Unit => {
+                        write!(f, "fn({}) -> {ret}", args.join(", "))
+                    }
+                    UnresolvedType::Tuple(env_types) => {
+                        let env_types = vecmap(env_types, ToString::to_string);
+                        write!(f, "fn[{}]({}) -> {ret}", env_types.join(", "), args.join(", "))
+                    }
+                    _ => unreachable!(),
+                }
             }
             MutableReference(element) => write!(f, "&mut {element}"),
             Unit => write!(f, "()"),

crates/noirc_frontend/src/hir/resolution/resolver.rs

@@ -361,10 +361,10 @@ impl<'a> Resolver<'a> {
             UnresolvedType::Tuple(fields) => {
                 Type::Tuple(vecmap(fields, |field| self.resolve_type_inner(field, new_variables)))
             }
-            UnresolvedType::Function(args, ret) => {
+            UnresolvedType::Function(args, ret, env) => {
                 let args = vecmap(args, |arg| self.resolve_type_inner(arg, new_variables));
                 let ret = Box::new(self.resolve_type_inner(*ret, new_variables));
-                let env = Box::new(Type::Unit);
+                let env = Box::new(self.resolve_type_inner(*env, new_variables));
                 Type::Function(args, ret, env)
             }
             UnresolvedType::MutableReference(element) => {

crates/noirc_frontend/src/hir/type_check/expr.rs

@@ -837,13 +837,11 @@ impl<'interner> TypeChecker<'interner> {
         }
 
         for (param, (arg, _, arg_span)) in fn_params.iter().zip(callsite_args) {
-            if arg.try_unify_allow_incompat_lambdas(param).is_err() {
-                self.errors.push(TypeCheckError::TypeMismatch {
-                    expected_typ: param.to_string(),
-                    expr_typ: arg.to_string(),
-                    expr_span: *arg_span,
-                });
-            }
+            self.unify(arg, param, || TypeCheckError::TypeMismatch {
+                expected_typ: param.to_string(),
+                expr_typ: arg.to_string(),
+                expr_span: *arg_span,
+            });
         }
 
         fn_ret.clone()

crates/noirc_frontend/src/hir/type_check/mod.rs

@@ -63,33 +63,28 @@ pub fn type_check_func(interner: &mut NodeInterner, func_id: FuncId) -> Vec<Type
         let (expr_span, empty_function) = function_info(interner, function_body_id);
 
         let func_span = interner.expr_span(function_body_id); // XXX: We could be more specific and return the span of the last stmt, however stmts do not have spans yet
+        function_last_type.unify_with_coercions(
+            &declared_return_type,
+            *function_body_id,
+            interner,
+            &mut errors,
+            || {
+                let mut error = TypeCheckError::TypeMismatchWithSource {
+                    expected: declared_return_type.clone(),
+                    actual: function_last_type.clone(),
+                    span: func_span,
+                    source: Source::Return(meta.return_type, expr_span),
+                };
 
-        let result = function_last_type.try_unify_allow_incompat_lambdas(&declared_return_type);
-
-        if result.is_err() {
-            function_last_type.unify_with_coercions(
-                &declared_return_type,
-                *function_body_id,
-                interner,
-                &mut errors,
-                || {
-                    let mut error = TypeCheckError::TypeMismatchWithSource {
-                        expected: declared_return_type.clone(),
-                        actual: function_last_type.clone(),
-                        span: func_span,
-                        source: Source::Return(meta.return_type, expr_span),
-                    };
-
-                    if empty_function {
-                        error = error.add_context(
-                            "implicitly returns `()` as its body has no tail or `return` expression",
-                        );
-                    }
+                if empty_function {
+                    error = error.add_context(
+                        "implicitly returns `()` as its body has no tail or `return` expression",
+                    );
+                }
 
-                    error
-                },
-            );
-        }
+                error
+            },
+        );
     }
 
     errors

crates/noirc_frontend/src/hir_def/types.rs

@@ -947,35 +947,6 @@ impl Type {
         }
     }
 
-    /// Similar to try_unify() but allows non-matching capture groups for function types
-    pub fn try_unify_allow_incompat_lambdas(&self, other: &Type) -> Result<(), UnificationError> {
-        use Type::*;
-        use TypeVariableKind::*;
-
-        match (self, other) {
-            (TypeVariable(binding, Normal), other) | (other, TypeVariable(binding, Normal)) => {
-                if let TypeBinding::Bound(link) = &*binding.borrow() {
-                    return link.try_unify_allow_incompat_lambdas(other);
-                }
-
-                other.try_bind_to(binding)
-            }
-            (Function(params_a, ret_a, _), Function(params_b, ret_b, _)) => {
-                if params_a.len() == params_b.len() {
-                    for (a, b) in params_a.iter().zip(params_b.iter()) {
-                        a.try_unify_allow_incompat_lambdas(b)?;
-                    }
-
-                    // no check for environments here!
-                    ret_b.try_unify_allow_incompat_lambdas(ret_a)
-                } else {
-                    Err(UnificationError)
-                }
-            }
-            _ => self.try_unify(other),
-        }
-    }
-
     /// Similar to `unify` but if the check fails this will attempt to coerce the
     /// argument to the target type. When this happens, the given expression is wrapped in
     /// a new expression to convert its type. E.g. `array` -> `array.as_slice()`

crates/noirc_frontend/src/monomorphization/mod.rs

@@ -784,15 +784,27 @@ impl<'interner> Monomorphizer<'interner> {
 
         let is_closure = self.is_function_closure(call.func);
         if is_closure {
-            let extracted_func: ast::Expression;
-            let hir_call_func = self.interner.expression(&call.func);
-            if let HirExpression::Lambda(l) = hir_call_func {
-                let (setup, closure_variable) = self.lambda_with_setup(l, call.func);
-                block_expressions.push(setup);
-                extracted_func = closure_variable;
-            } else {
-                extracted_func = *original_func;
-            }
+            let local_id = self.next_local_id();
+
+            // store the function in a temporary variable before calling it
+            // this is needed for example if call.func is of the form `foo()()`
+            // without this, we would translate it to `foo().1(foo().0)`
+            let let_stmt = ast::Expression::Let(ast::Let {
+                id: local_id,
+                mutable: false,
+                name: "tmp".to_string(),
+                expression: Box::new(*original_func),
+            });
+            block_expressions.push(let_stmt);
+
+            let extracted_func = ast::Expression::Ident(ast::Ident {
+                location: None,
+                definition: Definition::Local(local_id),
+                mutable: false,
+                name: "tmp".to_string(),
+                typ: Self::convert_type(&self.interner.id_type(call.func)),
+            });
+
             func = Box::new(ast::Expression::ExtractTupleField(
                 Box::new(extracted_func.clone()),
                 1usize,
@@ -1435,7 +1447,7 @@ mod tests {
     #[test]
     fn simple_closure_with_no_captured_variables() {
         let src = r#"
-        fn main() -> Field {
+        fn main() -> pub Field {
             let x = 1;
             let closure = || x;
             closure()
@@ -1451,7 +1463,10 @@ mod tests {
         };
         closure_variable$l2
     };
-    closure$l3.1(closure$l3.0)
+    {
+        let tmp$4 = closure$l3;
+        tmp$l4.1(tmp$l4.0)
+    }
 }
 fn lambda$f1(mut env$l1: (Field)) -> Field {
     env$l1.0

crates/noirc_frontend/src/parser/parser.rs

@@ -971,12 +971,30 @@ fn function_type<T>(type_parser: T) -> impl NoirParser<UnresolvedType>
 where
     T: NoirParser<UnresolvedType>,
 {
-    let args = parenthesized(type_parser.clone().separated_by(just(Token::Comma)).allow_trailing());
+    let types = type_parser.clone().separated_by(just(Token::Comma)).allow_trailing();
+    let args = parenthesized(types.clone());
+
+    let env = just(Token::LeftBracket)
+        .ignore_then(types)
+        .then_ignore(just(Token::RightBracket))
+        .or_not()
+        .map(|args| match args {
+            Some(args) => {
+                if args.is_empty() {
+                    UnresolvedType::Unit
+                } else {
+                    UnresolvedType::Tuple(args)
+                }
+            }
+            None => UnresolvedType::Unit,
+        });
+
     keyword(Keyword::Fn)
-        .ignore_then(args)
+        .ignore_then(env)
+        .then(args)
         .then_ignore(just(Token::Arrow))
         .then(type_parser)
-        .map(|(args, ret)| UnresolvedType::Function(args, Box::new(ret)))
+        .map(|((env, args), ret)| UnresolvedType::Function(args, Box::new(ret), Box::new(env)))
 }
 
 fn mutable_reference_type<T>(type_parser: T) -> impl NoirParser<UnresolvedType>