feat: Implement parsing of traits (#1886)

* Parse traits

* Fix modifier ordering

crates/noirc_frontend/src/ast/expression.rs

@@ -1,7 +1,7 @@
 use std::fmt::Display;
 
 use crate::token::{Attribute, Token};
-use crate::{Ident, Path, Pattern, Recoverable, Statement, UnresolvedType};
+use crate::{Ident, Path, Pattern, Recoverable, Statement, TraitConstraint, UnresolvedType};
 use acvm::FieldElement;
 use iter_extended::vecmap;
 use noirc_errors::{Span, Spanned};
@@ -337,6 +337,7 @@ pub struct FunctionDefinition {
     pub parameters: Vec<(Pattern, UnresolvedType, noirc_abi::AbiVisibility)>,
     pub body: BlockExpression,
     pub span: Span,
+    pub where_clause: Vec<TraitConstraint>,
     pub return_type: UnresolvedType,
     pub return_visibility: noirc_abi::AbiVisibility,
     pub return_distinctness: noirc_abi::AbiDistinctness,

crates/noirc_frontend/src/ast/mod.rs

@@ -8,13 +8,15 @@ mod expression;
 mod function;
 mod statement;
 mod structure;
+mod traits;
 
 pub use expression::*;
 pub use function::*;
 
 use noirc_errors::Span;
 pub use statement::*;
 pub use structure::*;
+pub use traits::*;
 
 use crate::{
     parser::{ParserError, ParserErrorReason},

crates/noirc_frontend/src/ast/statement.rs

@@ -424,6 +424,14 @@ impl Pattern {
             _ => panic!("only the identifier pattern can return a name"),
         }
     }
+
+    pub(crate) fn into_ident(self) -> Ident {
+        match self {
+            Pattern::Identifier(ident) => ident,
+            Pattern::Mutable(pattern, _) => pattern.into_ident(),
+            other => panic!("Pattern::into_ident called on {other} pattern with no identifier"),
+        }
+    }
 }
 
 impl Recoverable for Pattern {

crates/noirc_frontend/src/ast/structure.rs

@@ -1,6 +1,6 @@
 use std::fmt::Display;
 
-use crate::{Ident, NoirFunction, UnresolvedGenerics, UnresolvedType};
+use crate::{Ident, UnresolvedGenerics, UnresolvedType};
 use iter_extended::vecmap;
 use noirc_errors::Span;
 
@@ -24,15 +24,6 @@ impl NoirStruct {
     }
 }
 
-/// Ast node for an impl
-#[derive(Clone, Debug)]
-pub struct NoirImpl {
-    pub object_type: UnresolvedType,
-    pub type_span: Span,
-    pub generics: UnresolvedGenerics,
-    pub methods: Vec<NoirFunction>,
-}
-
 impl Display for NoirStruct {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let generics = vecmap(&self.generics, |generic| generic.to_string());
@@ -47,21 +38,3 @@ impl Display for NoirStruct {
         write!(f, "}}")
     }
 }
-
-impl Display for NoirImpl {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        let generics = vecmap(&self.generics, |generic| generic.to_string());
-        let generics = if generics.is_empty() { "".into() } else { generics.join(", ") };
-
-        writeln!(f, "impl{} {} {{", generics, self.object_type)?;
-
-        for method in self.methods.iter() {
-            let method = method.to_string();
-            for line in method.lines() {
-                writeln!(f, "    {line}")?;
-            }
-        }
-
-        write!(f, "}}")
-    }
-}

crates/noirc_frontend/src/ast/traits.rs

@@ -0,0 +1,165 @@
+use std::fmt::Display;
+
+use iter_extended::vecmap;
+use noirc_errors::Span;
+
+use crate::{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 items: Vec<TraitItem>,
+}
+
+/// Any declaration inside the body of a trait that a user is required to
+/// specify when implementing the trait.
+#[derive(Clone, Debug)]
+pub enum TraitItem {
+    Function {
+        name: Ident,
+        generics: Vec<Ident>,
+        parameters: Vec<(Ident, UnresolvedType)>,
+        return_type: UnresolvedType,
+        where_clause: Vec<TraitConstraint>,
+    },
+    Type {
+        name: Ident,
+    },
+}
+
+/// Ast node for an impl of a concrete type
+/// `impl object_type<generics> { ... methods ... }`
+#[derive(Clone, Debug)]
+pub struct TypeImpl {
+    pub object_type: UnresolvedType,
+    pub type_span: Span,
+    pub generics: UnresolvedGenerics,
+    pub methods: Vec<NoirFunction>,
+}
+
+/// Ast node for an implementation of a trait for a particular type
+/// `impl trait_name<trait_generics> for object_type where where_clauses { ... items ... }`
+#[derive(Clone, Debug)]
+pub struct TraitImpl {
+    pub impl_generics: UnresolvedGenerics,
+
+    pub trait_name: Ident,
+    pub trait_generics: Vec<UnresolvedType>,
+
+    pub object_type: UnresolvedType,
+    pub object_type_span: Span,
+
+    pub where_clause: Vec<TraitConstraint>,
+
+    pub items: Vec<TraitImplItem>,
+}
+
+/// Represents a trait constraint such as `where Foo: Display`
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct TraitConstraint {
+    pub typ: UnresolvedType,
+    pub trait_name: Ident,
+    pub trait_generics: Vec<UnresolvedType>,
+}
+
+#[derive(Clone, Debug)]
+pub enum TraitImplItem {
+    Function(NoirFunction),
+    Type { name: Ident, alias: UnresolvedType },
+}
+
+impl Display for TypeImpl {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let generics = vecmap(&self.generics, |generic| generic.to_string());
+        let generics = if generics.is_empty() { "".into() } else { generics.join(", ") };
+
+        writeln!(f, "impl{} {} {{", generics, self.object_type)?;
+
+        for method in self.methods.iter() {
+            let method = method.to_string();
+            for line in method.lines() {
+                writeln!(f, "    {line}")?;
+            }
+        }
+
+        write!(f, "}}")
+    }
+}
+
+impl Display for NoirTrait {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let generics = vecmap(&self.generics, |generic| generic.to_string());
+        let generics = if generics.is_empty() { "".into() } else { generics.join(", ") };
+
+        writeln!(f, "trait {}{} {{", self.name, generics)?;
+
+        for item in self.items.iter() {
+            let item = item.to_string();
+            for line in item.lines() {
+                writeln!(f, "    {line}")?;
+            }
+        }
+
+        write!(f, "}}")
+    }
+}
+
+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 } => {
+                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);
+
+                let generics = generics.join(", ");
+                let parameters = parameters.join(", ");
+                let where_clause = where_clause.join(", ");
+
+                write!(
+                    f,
+                    "fn {name}<{}>({}) -> {} where {};",
+                    generics, parameters, return_type, where_clause
+                )
+            }
+            TraitItem::Type { name } => write!(f, "type {name};"),
+        }
+    }
+}
+
+impl Display for TraitConstraint {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let generics = vecmap(&self.trait_generics, |generic| generic.to_string());
+        write!(f, "{}: {}<{}>", self.typ, self.trait_name, generics.join(", "))
+    }
+}
+
+impl Display for TraitImpl {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let generics = vecmap(&self.trait_generics, |generic| generic.to_string());
+        let generics = generics.join(", ");
+
+        writeln!(f, "impl {}<{}> for {} {{", self.trait_name, generics, self.object_type)?;
+
+        for item in self.items.iter() {
+            let item = item.to_string();
+            for line in item.lines() {
+                writeln!(f, "    {line}")?;
+            }
+        }
+
+        write!(f, "}}")
+    }
+}
+
+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}"),
+        }
+    }
+}

crates/noirc_frontend/src/hir/def_collector/dc_mod.rs

@@ -3,7 +3,7 @@ use noirc_errors::FileDiagnostic;
 
 use crate::{
     graph::CrateId, hir::def_collector::dc_crate::UnresolvedStruct, node_interner::StructId,
-    parser::SubModule, Ident, LetStatement, NoirFunction, NoirImpl, NoirStruct, ParsedModule,
+    parser::SubModule, Ident, LetStatement, NoirFunction, NoirStruct, ParsedModule, TypeImpl,
 };
 
 use super::{
@@ -92,7 +92,7 @@ impl<'a> ModCollector<'a> {
         }
     }
 
-    fn collect_impls(&mut self, context: &mut Context, impls: Vec<NoirImpl>) {
+    fn collect_impls(&mut self, context: &mut Context, impls: Vec<TypeImpl>) {
         for r#impl in impls {
             let mut unresolved_functions =
                 UnresolvedFunctions { file_id: self.file_id, functions: Vec::new() };

crates/noirc_frontend/src/lexer/token.rs

@@ -428,20 +428,23 @@ pub enum Keyword {
     Fn,
     For,
     Global,
-    Impl,
     If,
+    Impl,
     In,
     Internal,
     Let,
     Mod,
     Mut,
     Open,
     Pub,
-    String,
     Return,
+    String,
     Struct,
+    Trait,
+    Type,
     Unconstrained,
     Use,
+    Where,
     While,
 }
 
@@ -463,20 +466,23 @@ impl fmt::Display for Keyword {
             Keyword::Fn => write!(f, "fn"),
             Keyword::For => write!(f, "for"),
             Keyword::Global => write!(f, "global"),
-            Keyword::Impl => write!(f, "impl"),
             Keyword::If => write!(f, "if"),
+            Keyword::Impl => write!(f, "impl"),
             Keyword::In => write!(f, "in"),
             Keyword::Internal => write!(f, "internal"),
             Keyword::Let => write!(f, "let"),
             Keyword::Mod => write!(f, "mod"),
             Keyword::Mut => write!(f, "mut"),
             Keyword::Open => write!(f, "open"),
             Keyword::Pub => write!(f, "pub"),
-            Keyword::String => write!(f, "str"),
             Keyword::Return => write!(f, "return"),
+            Keyword::String => write!(f, "str"),
             Keyword::Struct => write!(f, "struct"),
+            Keyword::Trait => write!(f, "trait"),
+            Keyword::Type => write!(f, "type"),
             Keyword::Unconstrained => write!(f, "unconstrained"),
             Keyword::Use => write!(f, "use"),
+            Keyword::Where => write!(f, "where"),
             Keyword::While => write!(f, "while"),
         }
     }
@@ -501,20 +507,23 @@ impl Keyword {
             "fn" => Keyword::Fn,
             "for" => Keyword::For,
             "global" => Keyword::Global,
-            "impl" => Keyword::Impl,
             "if" => Keyword::If,
+            "impl" => Keyword::Impl,
             "in" => Keyword::In,
             "internal" => Keyword::Internal,
             "let" => Keyword::Let,
             "mod" => Keyword::Mod,
             "mut" => Keyword::Mut,
             "open" => Keyword::Open,
             "pub" => Keyword::Pub,
-            "str" => Keyword::String,
             "return" => Keyword::Return,
+            "str" => Keyword::String,
             "struct" => Keyword::Struct,
+            "trait" => Keyword::Trait,
+            "type" => Keyword::Type,
             "unconstrained" => Keyword::Unconstrained,
             "use" => Keyword::Use,
+            "where" => Keyword::Where,
             "while" => Keyword::While,
 
             "true" => return Some(Token::Bool(true)),

crates/noirc_frontend/src/parser/errors.rs

@@ -21,6 +21,10 @@ pub enum ParserErrorReason {
     InvalidArrayLengthExpression(Expression),
     #[error("Early 'return' is unsupported")]
     EarlyReturn,
+    #[error("Patterns aren't allowed in a trait's function declarations")]
+    PatternInTraitFunctionParameter,
+    #[error("Traits are an experimental feature that are not yet in a working state")]
+    TraitsAreExperimental,
 }
 
 /// Represents a parsing error, or a parsing error in the making.