feat: Implement traits - parser support noir-lang#2094

* Add several parsing traits test
* Expand trait definition in AST to include body
* Add diagnostic error when where clause is not appled on generic type

crates/noirc_errors/src/reporter.rs

@@ -74,6 +74,10 @@ impl CustomDiagnostic {
     pub fn is_error(&self) -> bool {
         matches!(self.kind, DiagnosticKind::Error)
     }
+
+    pub fn is_warrning(&self) -> bool {
+        matches!(self.kind, DiagnosticKind::Warning)
+    }
 }
 
 impl std::fmt::Display for CustomDiagnostic {

crates/noirc_frontend/src/ast/traits.rs

@@ -3,14 +3,16 @@ use std::fmt::Display;
 use iter_extended::vecmap;
 use noirc_errors::Span;
 
-use crate::{Ident, NoirFunction, UnresolvedGenerics, UnresolvedType};
+use crate::{BlockExpression, Expression, Ident, NoirFunction, UnresolvedGenerics, UnresolvedType};
 
 /// AST node for trait definitions:
 /// `trait name<generics> { ... items ... }`
 #[derive(Clone, Debug)]
 pub struct NoirTrait {
     pub name: Ident,
     pub generics: Vec<Ident>,
+    pub where_clause: Vec<TraitConstraint>,
+    pub span: Span,
     pub items: Vec<TraitItem>,
 }
 
@@ -24,6 +26,12 @@ pub enum TraitItem {
         parameters: Vec<(Ident, UnresolvedType)>,
         return_type: UnresolvedType,
         where_clause: Vec<TraitConstraint>,
+        body: Option<BlockExpression>,
+    },
+    Constant {
+        name: Ident,
+        typ: UnresolvedType,
+        default_value: Option<Expression>,
     },
     Type {
         name: Ident,
@@ -68,6 +76,7 @@ pub struct TraitConstraint {
 #[derive(Clone, Debug)]
 pub enum TraitImplItem {
     Function(NoirFunction),
+    Constant(Ident, UnresolvedType, Expression),
     Type { name: Ident, alias: UnresolvedType },
 }
 
@@ -110,7 +119,7 @@ impl Display for NoirTrait {
 impl Display for TraitItem {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            TraitItem::Function { name, generics, parameters, return_type, where_clause } => {
+            TraitItem::Function { name, generics, parameters, return_type, where_clause, body } => {
                 let generics = vecmap(generics, |generic| generic.to_string());
                 let parameters = vecmap(parameters, |(name, typ)| format!("{name}: {typ}"));
                 let where_clause = vecmap(where_clause, ToString::to_string);
@@ -121,9 +130,24 @@ impl Display for TraitItem {
 
                 write!(
                     f,
-                    "fn {name}<{}>({}) -> {} where {};",
+                    "fn {name}<{}>({}) -> {} where {}",
                     generics, parameters, return_type, where_clause
-                )
+                )?;
+
+                if let Some(body) = body {
+                    write!(f, "{}", body)
+                } else {
+                    write!(f, ";")
+                }
+            }
+            TraitItem::Constant { name, typ, default_value } => {
+                write!(f, "let {}: {}", name, typ)?;
+
+                if let Some(default_value) = default_value {
+                    write!(f, "{};", default_value)
+                } else {
+                    write!(f, ";")
+                }
             }
             TraitItem::Type { name } => write!(f, "type {name};"),
         }
@@ -159,7 +183,10 @@ impl Display for TraitImplItem {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             TraitImplItem::Function(function) => function.fmt(f),
-            TraitImplItem::Type { name, alias } => write!(f, "type {name} = {alias}"),
+            TraitImplItem::Type { name, alias } => write!(f, "type {name} = {alias};"),
+            TraitImplItem::Constant(name, typ, value) => {
+                write!(f, "let {}: {} = {};", name, typ, value)
+            }
         }
     }
 }

crates/noirc_frontend/src/parser/errors.rs

@@ -29,6 +29,8 @@ pub enum ParserErrorReason {
     ComptimeDeprecated,
     #[error("{0} are experimental and aren't fully supported yet")]
     ExperimentalFeature(&'static str),
+    #[error("Where clauses are allowed only on functions with generic parameters")]
+    WhereClauseOnNonGenericFunction,
 }
 
 /// Represents a parsing error, or a parsing error in the making.

crates/noirc_frontend/src/parser/parser.rs

@@ -168,9 +168,9 @@ fn function_definition(allow_self: bool) -> impl NoirParser<NoirFunction> {
         .then(function_return_type())
         .then(where_clause())
         .then(block(expression()))
-        .map(|(((args, ret), where_clause), body)| {
+        .validate(|(((args, ret), where_clause), body), span, emit| {
             let ((((attribute, modifiers), name), generics), parameters) = args;
-
+            validate_where_clause(&generics, &where_clause, span, emit);
             FunctionDefinition {
                 span: name.0.span(),
                 name,
@@ -364,22 +364,38 @@ fn trait_definition() -> impl NoirParser<TopLevelStatement> {
     keyword(Keyword::Trait)
         .ignore_then(ident())
         .then(generics())
+        .then(where_clause())
         .then_ignore(just(Token::LeftBrace))
         .then(trait_body())
         .then_ignore(just(Token::RightBrace))
-        .validate(|((name, generics), items), span, emit| {
+        .validate(|(((name, generics), where_clause), items), span, emit| {
+            validate_where_clause(&generics, &where_clause, span, emit);
             emit(ParserError::with_reason(ParserErrorReason::ExperimentalFeature("Traits"), span));
-            TopLevelStatement::Trait(NoirTrait { name, generics, items })
+            TopLevelStatement::Trait(NoirTrait { name, generics, where_clause, span, items })
         })
 }
 
 fn trait_body() -> impl NoirParser<Vec<TraitItem>> {
     trait_function_declaration()
         .or(trait_type_declaration())
+        .or(trait_constant_declaration())
         .separated_by(just(Token::Semicolon))
         .allow_trailing()
 }
 
+fn optional_default_value() -> impl NoirParser<Option<Expression>> {
+    ignore_then_commit(just(Token::Assign), expression()).or_not()
+}
+
+fn trait_constant_declaration() -> impl NoirParser<TraitItem> {
+    keyword(Keyword::Let)
+        .ignore_then(ident())
+        .then_ignore(just(Token::Colon))
+        .then(parse_type())
+        .then(optional_default_value())
+        .map(|((name, typ), default_value)| TraitItem::Constant { name, typ, default_value })
+}
+
 /// trait_function_declaration: 'fn' ident generics '(' declaration_parameters ')' function_return_type
 fn trait_function_declaration() -> impl NoirParser<TraitItem> {
     keyword(Keyword::Fn)
@@ -388,13 +404,31 @@ fn trait_function_declaration() -> impl NoirParser<TraitItem> {
         .then(parenthesized(function_declaration_parameters()))
         .then(function_return_type().map(|(_, typ)| typ))
         .then(where_clause())
-        .map(|((((name, generics), parameters), return_type), where_clause)| TraitItem::Function {
-            name,
-            generics,
-            parameters,
-            return_type,
-            where_clause,
-        })
+        .then(block(expression()).or_not())
+        .validate(
+            |(((((name, generics), parameters), return_type), where_clause), body), span, emit| {
+                validate_where_clause(&generics, &where_clause, span, emit);
+                TraitItem::Function { name, generics, parameters, return_type, where_clause, body }
+            },
+        )
+}
+
+fn validate_where_clause(
+    generics: &Vec<Ident>,
+    where_clause: &Vec<TraitConstraint>,
+    span: Span,
+    emit: &mut dyn FnMut(ParserError),
+) {
+    if !where_clause.is_empty() && generics.is_empty() {
+        emit(ParserError::with_reason(ParserErrorReason::WhereClauseOnNonGenericFunction, span));
+    }
+
+    // TODO(GenericParameterNotFoundInFunction):
+    // Even though Rust supports where clauses that don't mention any of the generic
+    // parameters, these are of dubious value and can be accidentally produced by
+    // typos in the code, so we can consider producing compile-time errors for them.
+    //
+    // https://doc.rust-lang.org/reference/items/generics.html#where-clauses
 }
 
 /// Function declaration parameters differ from other parameters in that parameter
@@ -403,9 +437,8 @@ fn function_declaration_parameters() -> impl NoirParser<Vec<(Ident, UnresolvedTy
     let typ = parse_type().recover_via(parameter_recovery());
     let typ = just(Token::Colon).ignore_then(typ);
 
-    let parameter = ident().recover_via(parameter_name_recovery()).then(typ);
-
-    let parameter = parameter.or(self_parameter().validate(|param, span, emit| {
+    let full_parameter = ident().recover_via(parameter_name_recovery()).then(typ);
+    let self_parameter = self_parameter().validate(|param, span, emit| {
         match param.0 {
             Pattern::Identifier(ident) => (ident, param.1),
             other => {
@@ -418,7 +451,9 @@ fn function_declaration_parameters() -> impl NoirParser<Vec<(Ident, UnresolvedTy
                 (other.into_ident(), param.1)
             }
         }
-    }));
+    });
+
+    let parameter = full_parameter.or(self_parameter);
 
     parameter
         .separated_by(just(Token::Comma))
@@ -504,7 +539,7 @@ fn where_clause() -> impl NoirParser<Vec<TraitConstraint>> {
         });
 
     keyword(Keyword::Where)
-        .ignore_then(constraints.repeated())
+        .ignore_then(constraints.separated_by(just(Token::Comma)))
         .or_not()
         .map(|option| option.unwrap_or_default())
 }
@@ -1444,6 +1479,22 @@ mod test {
         })
     }
 
+    fn parse_all_ignore_warnings<P, T>(parser: P, programs: Vec<&str>) -> Vec<T>
+    where
+        P: NoirParser<T>,
+    {
+        vecmap(programs, move |program| {
+            let message = format!("Failed to parse:\n{}", program);
+            let (op_t, errors) = parse_recover(&parser, program);
+            for e in errors {
+                if !e.is_warrning() {
+                    panic!("{}", &message);
+                }
+            }
+            op_t.expect(&message)
+        })
+    }
+
     fn parse_all_failing<P, T>(parser: P, programs: Vec<&str>) -> Vec<CustomDiagnostic>
     where
         P: NoirParser<T>,
@@ -1743,14 +1794,70 @@ mod test {
                 "fn f(foo: pub u8, y : pub Field) -> u8 { x + a }",
                 "fn f(f: pub Field, y : Field, z : Field) -> u8 { x + a }",
                 "fn func_name(f: Field, y : pub Field, z : pub [u8;5],) {}",
+                "fn f(f: pub Field, y : Field, z : Field) -> u8 { x + a }",
+                "fn f<T>(f: pub Field, y : T, z : Field) -> u8 { x + a }",
                 "fn func_name(x: [Field], y : [Field;2],y : pub [Field;2], z : pub [u8;5])  {}",
                 "fn main(x: pub u8, y: pub u8) -> distinct pub [u8; 2] { [x, y] }",
             ],
         );
 
+        parse_all_ignore_warnings(
+            function_definition(false),
+            vec![
+                "fn f(f: pub Field, y : Field, z : comptime Field) -> u8 { x + a }",
+                "fn f<T>(f: pub Field, y : T, z : comptime Field) -> u8 { x + a }",
+                "fn func_name<T>(f: Field, y : T) where T: SomeTrait {}",
+            ],
+        );
+
         parse_all_failing(
             function_definition(false),
-            vec!["fn x2( f: []Field,,) {}", "fn ( f: []Field) {}", "fn ( f: []Field) {}"],
+            vec![
+                "fn x2( f: []Field,,) {}",
+                "fn ( f: []Field) {}",
+                "fn ( f: []Field) {}",
+                // TODO: Check for more specific error messages
+                "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) where T: {}",
+                "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) where SomeTrait {}",
+                "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) SomeTrait {}",
+                "fn func_name(f: Field, y : pub Field, z : pub [u8;5],) where T: SomeTrait {}",
+                // TODO(GenericParameterNotFoundInFunction)
+                // Consider making this a compilation error:
+                // "fn func_name<A>(f: Field, y : pub Field, z : pub [u8;5],) where T: SomeTrait {}",
+            ],
+        );
+    }
+
+    #[test]
+    fn parse_trait() {
+        parse_all_ignore_warnings(
+            trait_definition(),
+            vec![
+                // Empty traits are legal in Rust and sometimes used as a way to whitelist certain types
+                // for a particular operation. Also known as `tag` or `marker` traits:
+                // https://stackoverflow.com/questions/71895489/what-is-the-purpose-of-defining-empty-impl-in-rust
+                "trait Empty {}",
+                "trait TraitWithDefaultBody { fn foo(self) {}; }",
+                "trait TraitAcceptingMutableRef { fn foo(&mut self); }",
+                "trait TraitWithTypeBoundOperation { fn identity() -> Self; }",
+                "trait TraitWithAssociatedType { type Element; fn item(self, index: Field) -> Self::Element; }",
+                "trait TraitWithAssociatedConstant { let Size: Field; }",
+                "trait TraitWithAssociatedConstantWithDefaultValue { let Size: Field = 10; }",
+            ],
+        );
+
+        parse_all_failing(
+            trait_definition(),
+            vec![
+                "trait MissingBody",
+                "trait WrongDelimiter { fn foo() -> u8, fn bar() -> u8 }",
+                "trait WhereClauseWithoutGenerics where A: SomeTrait { }",
+                // TODO: when implemnt generics in traits the following 3 should pass
+                "trait GenericTrait<T> { fn elem(&mut self, index: Field) -> T; }",
+                "trait GenericTraitWithConstraints<T> where T: SomeTrait { fn elem(self, index: Field) -> T; }",
+                "trait TraitWithMultipleGenericParams<A, B, C> where A: SomeTrait, B: AnotherTrait<C> { comptime Size: Field; fn zero() -> Self; }",
+
+            ],
         );
     }