Treat trait exclusively as Item not Type

crates/analyzer/src/db/queries/contracts.rs

@@ -330,14 +330,6 @@ pub fn contract_field_type(
 
     let node = &field.data(db).ast;
 
-    if let Ok(Type::Trait(ref val)) = typ {
-        scope.error(
-            "traits can not be used as contract fields",
-            node.span,
-            &format!("trait `{}` can not appear here", val.name),
-        );
-    }
-
     if node.kind.is_pub {
         scope.not_yet_implemented("contract `pub` fields", node.span);
     }

crates/analyzer/src/db/queries/functions.rs

@@ -7,7 +7,7 @@ use crate::namespace::items::{
 use crate::namespace::scopes::{BlockScope, BlockScopeType, FunctionScope, ItemScope};
 use crate::namespace::types::{self, Contract, CtxDecl, Generic, SelfDecl, Struct, Type};
 use crate::traversal::functions::traverse_statements;
-use crate::traversal::types::type_desc;
+use crate::traversal::types::{type_desc, type_desc_to_trait};
 use fe_common::diagnostics::Label;
 use fe_parser::ast::{self, GenericParameter};
 use fe_parser::node::Node;
@@ -255,17 +255,9 @@ pub fn resolve_function_param_type(
         if let Some(val) = function.generic_param(db, base) {
             let bounds = match val {
                 ast::GenericParameter::Unbounded(_) => vec![],
-                ast::GenericParameter::Bounded { bound, .. } => match type_desc(context, &bound)? {
-                    Type::Trait(trait_ty) => vec![trait_ty.id],
-                    other => {
-                        context.error(
-                            &format!("expected trait, found type `{}`", other),
-                            bound.span,
-                            "not a trait",
-                        );
-                        vec![]
-                    }
-                },
+                ast::GenericParameter::Bounded { bound, .. } => {
+                    vec![type_desc_to_trait(context, &bound)?]
+                }
             };
 
             return Ok(Type::Generic(Generic {
@@ -401,11 +393,7 @@ pub fn function_dependency_graph(db: &dyn AnalyzerDb, function: FunctionId) -> D
                 directs.push((root, Item::Function(*method), DepLocality::Local));
             }
             CallType::TraitValueMethod { trait_id, .. } => {
-                directs.push((
-                    root,
-                    Item::Type(TypeDef::Trait(*trait_id)),
-                    DepLocality::Local,
-                ));
+                directs.push((root, Item::Trait(*trait_id), DepLocality::Local));
             }
             CallType::External { contract, function } => {
                 directs.push((root, Item::Function(*function), DepLocality::External));

crates/analyzer/src/db/queries/module.rs

@@ -89,12 +89,10 @@ pub fn module_all_items(db: &dyn AnalyzerDb, module: ModuleId) -> Rc<[Item]> {
             ast::ModuleStmt::Function(node) => Some(Item::Function(
                 db.intern_function(Rc::new(Function::new(db, node, None, module))),
             )),
-            ast::ModuleStmt::Trait(node) => Some(Item::Type(TypeDef::Trait(db.intern_trait(
-                Rc::new(Trait {
-                    ast: node.clone(),
-                    module,
-                }),
-            )))),
+            ast::ModuleStmt::Trait(node) => Some(Item::Trait(db.intern_trait(Rc::new(Trait {
+                ast: node.clone(),
+                module,
+            })))),
             ast::ModuleStmt::Pragma(_) | ast::ModuleStmt::Use(_) | ast::ModuleStmt::Impl(_) => None,
             ast::ModuleStmt::Event(node) => Some(Item::Event(db.intern_event(Rc::new(Event {
                 ast: node.clone(),
@@ -119,7 +117,7 @@ pub fn module_all_impls(db: &dyn AnalyzerDb, module: ModuleId) -> Rc<[ImplId]> {
                 let mut scope = ItemScope::new(db, module);
                 let receiver_type = type_desc(&mut scope, &impl_node.kind.receiver).unwrap();
 
-                if let Some(Item::Type(TypeDef::Trait(val))) = treit {
+                if let Some(Item::Trait(val)) = treit {
                     Some(db.intern_impl(Rc::new(Impl {
                         trait_id: val,
                         receiver: receiver_type,

crates/analyzer/src/namespace/items.rs

@@ -36,6 +36,7 @@ pub enum Item {
     // Events aren't normal types; they *could* be moved into
     // TypeDef, but it would have consequences.
     Event(EventId),
+    Trait(TraitId),
     Function(FunctionId),
     Constant(ModuleConstantId),
     // Needed until we can represent keccak256 as a FunctionId.
@@ -48,6 +49,7 @@ impl Item {
     pub fn name(&self, db: &dyn AnalyzerDb) -> SmolStr {
         match self {
             Item::Type(id) => id.name(db),
+            Item::Trait(id) => id.name(db),
             Item::GenericType(id) => id.name(),
             Item::Event(id) => id.name(db),
             Item::Function(id) => id.name(db),
@@ -62,6 +64,7 @@ impl Item {
     pub fn name_span(&self, db: &dyn AnalyzerDb) -> Option<Span> {
         match self {
             Item::Type(id) => id.name_span(db),
+            Item::Trait(id) => Some(id.name_span(db)),
             Item::GenericType(_) => None,
             Item::Event(id) => Some(id.name_span(db)),
             Item::Function(id) => Some(id.name_span(db)),
@@ -81,6 +84,7 @@ impl Item {
             | Self::Intrinsic(_)
             | Self::GenericType(_) => true,
             Self::Type(id) => id.is_public(db),
+            Self::Trait(id) => id.is_public(db),
             Self::Event(id) => id.is_public(db),
             Self::Function(id) => id.is_public(db),
             Self::Constant(id) => id.is_public(db),
@@ -94,6 +98,7 @@ impl Item {
             | Item::BuiltinFunction(_)
             | Item::Intrinsic(_) => true,
             Item::Type(_)
+            | Item::Trait(_)
             | Item::Event(_)
             | Item::Function(_)
             | Item::Constant(_)
@@ -113,6 +118,7 @@ impl Item {
     pub fn item_kind_display_name(&self) -> &'static str {
         match self {
             Item::Type(_) | Item::GenericType(_) => "type",
+            Item::Trait(_) => "trait",
             Item::Event(_) => "event",
             Item::Function(_) | Item::BuiltinFunction(_) => "function",
             Item::Intrinsic(_) => "intrinsic function",
@@ -129,6 +135,7 @@ impl Item {
             Item::Type(val) => val.items(db),
             Item::GenericType(_)
             | Item::Event(_)
+            | Item::Trait(_)
             | Item::Function(_)
             | Item::Constant(_)
             | Item::BuiltinFunction(_)
@@ -139,6 +146,7 @@ impl Item {
     pub fn parent(&self, db: &dyn AnalyzerDb) -> Option<Item> {
         match self {
             Item::Type(id) => id.parent(db),
+            Item::Trait(id) => Some(id.parent(db)),
             Item::GenericType(_) => None,
             Item::Event(id) => Some(id.parent(db)),
             Item::Function(id) => Some(id.parent(db)),
@@ -222,6 +230,7 @@ impl Item {
     pub fn sink_diagnostics(&self, db: &dyn AnalyzerDb, sink: &mut impl DiagnosticSink) {
         match self {
             Item::Type(id) => id.sink_diagnostics(db, sink),
+            Item::Trait(id) => id.sink_diagnostics(db, sink),
             Item::Event(id) => id.sink_diagnostics(db, sink),
             Item::Function(id) => id.sink_diagnostics(db, sink),
             Item::GenericType(_) | Item::BuiltinFunction(_) | Item::Intrinsic(_) => {}
@@ -772,7 +781,6 @@ impl ModuleConstantId {
 pub enum TypeDef {
     Alias(TypeAliasId),
     Struct(StructId),
-    Trait(TraitId),
     Contract(ContractId),
     Primitive(types::Base),
 }
@@ -804,7 +812,6 @@ impl TypeDef {
         match self {
             TypeDef::Alias(id) => id.name(db),
             TypeDef::Struct(id) => id.name(db),
-            TypeDef::Trait(id) => id.name(db),
             TypeDef::Contract(id) => id.name(db),
             TypeDef::Primitive(typ) => typ.name(),
         }
@@ -814,7 +821,6 @@ impl TypeDef {
         match self {
             TypeDef::Alias(id) => Some(id.name_span(db)),
             TypeDef::Struct(id) => Some(id.name_span(db)),
-            TypeDef::Trait(id) => Some(id.name_span(db)),
             TypeDef::Contract(id) => Some(id.name_span(db)),
             TypeDef::Primitive(_) => None,
         }
@@ -828,10 +834,6 @@ impl TypeDef {
                 name: id.name(db),
                 field_count: id.fields(db).len(), // for the EvmSized trait
             })),
-            TypeDef::Trait(id) => Ok(types::Type::Trait(types::Trait {
-                id: *id,
-                name: id.name(db),
-            })),
             TypeDef::Contract(id) => Ok(types::Type::Contract(types::Contract {
                 id: *id,
                 name: id.name(db),
@@ -844,7 +846,6 @@ impl TypeDef {
         match self {
             Self::Alias(id) => id.is_public(db),
             Self::Struct(id) => id.is_public(db),
-            Self::Trait(id) => id.is_public(db),
             Self::Contract(id) => id.is_public(db),
             Self::Primitive(_) => true,
         }
@@ -854,7 +855,6 @@ impl TypeDef {
         match self {
             TypeDef::Alias(id) => Some(id.parent(db)),
             TypeDef::Struct(id) => Some(id.parent(db)),
-            TypeDef::Trait(id) => Some(id.parent(db)),
             TypeDef::Contract(id) => Some(id.parent(db)),
             TypeDef::Primitive(_) => None,
         }
@@ -864,7 +864,6 @@ impl TypeDef {
         match self {
             TypeDef::Alias(id) => id.sink_diagnostics(db, sink),
             TypeDef::Struct(id) => id.sink_diagnostics(db, sink),
-            TypeDef::Trait(id) => id.sink_diagnostics(db, sink),
             TypeDef::Contract(id) => id.sink_diagnostics(db, sink),
             TypeDef::Primitive(_) => {}
         }
@@ -1158,7 +1157,7 @@ impl FunctionSigId {
     }
 
     pub fn is_trait_fn(&self, db: &dyn AnalyzerDb) -> bool {
-        matches!(self.parent(db), Item::Type(TypeDef::Trait(_)))
+        matches!(self.parent(db), Item::Trait(_))
     }
 
     pub fn is_impl_fn(&self, db: &dyn AnalyzerDb) -> bool {
@@ -1344,7 +1343,7 @@ impl Class {
         match self {
             Class::Contract(id) => Item::Type(TypeDef::Contract(*id)),
             Class::Struct(id) => Item::Type(TypeDef::Struct(*id)),
-            Class::Trait(id) => Item::Type(TypeDef::Trait(*id)),
+            Class::Trait(id) => Item::Trait(*id),
             // Coercing into an Item of the basis of the receiver doesn't seem ideal but can hopefully
             // be addressed when we get rid of `Class`.
             Class::Impl(id) => id
@@ -1595,7 +1594,6 @@ impl ImplId {
             Type::Contract(_)
             | Type::Map(_)
             | Type::SelfContract(_)
-            | Type::Trait(_)
             | Type::Generic(_)
             // TODO: We should find a way to support these types. We only support implementing traits for structs
             // so far because it simplifies things regarding the assign location of the underlying type.

crates/analyzer/src/namespace/types.rs

@@ -47,7 +47,6 @@ pub enum Type {
     /// of `self` within a contract function.
     SelfContract(Contract),
     Struct(Struct),
-    Trait(Trait),
     Generic(Generic),
 }
 
@@ -410,7 +409,6 @@ impl Type {
             Type::Tuple(inner) => inner.to_string().into(),
             Type::String(inner) => inner.to_string().into(),
             Type::Struct(inner) => inner.name.clone(),
-            Type::Trait(inner) => inner.name.clone(),
             Type::Generic(inner) => inner.name.clone(),
             Type::Contract(inner) | Type::SelfContract(inner) => inner.name.clone(),
         }
@@ -482,7 +480,7 @@ impl Type {
             | Type::Struct(_)
             | Type::Generic(_)
             | Type::Contract(_) => true,
-            Type::Map(_) | Type::SelfContract(_) | Type::Trait(_) => false,
+            Type::Map(_) | Type::SelfContract(_) => false,
         }
     }
 }
@@ -686,7 +684,6 @@ impl fmt::Display for Type {
             Type::Contract(inner) => inner.fmt(f),
             Type::SelfContract(inner) => inner.fmt(f),
             Type::Struct(inner) => inner.fmt(f),
-            Type::Trait(inner) => inner.fmt(f),
             Type::Generic(inner) => inner.fmt(f),
         }
     }

crates/analyzer/src/operations.rs

@@ -15,7 +15,6 @@ pub fn index(value: Type, index: Type) -> Result<Type, IndexingError> {
         | Type::String(_)
         | Type::Contract(_)
         | Type::SelfContract(_)
-        | Type::Trait(_)
         | Type::Generic(_)
         | Type::Struct(_) => Err(IndexingError::NotSubscriptable),
     }

crates/analyzer/src/traversal/expressions.rs

@@ -3,7 +3,6 @@ use crate::context::{AnalyzerContext, CallType, ExpressionAttributes, Location,
 use crate::errors::{FatalError, IndexingError};
 use crate::namespace::items::{Class, FunctionId, Item, TypeDef};
 use crate::namespace::scopes::BlockScopeType;
-use crate::namespace::types::Trait;
 use crate::namespace::types::{
     Array, Base, Contract, FeString, Integer, Struct, Tuple, Type, TypeDowncast, U256,
 };
@@ -179,7 +178,7 @@ pub fn assignable_expr(
                 attributes.move_location = Some(Location::Value);
             }
         }
-        Array(_) | Tuple(_) | String(_) | Struct(_) | Trait(_) | Generic(_) => {
+        Array(_) | Tuple(_) | String(_) | Struct(_) | Generic(_) => {
             if attributes.final_location() != Location::Memory {
                 context.fancy_error(
                     "value must be copied to memory",
@@ -318,10 +317,24 @@ fn expr_named_thing(
                         id.receiver(context.db()),
                         Location::Memory,
                     )),
-                    Class::Trait(id) => Ok(ExpressionAttributes::new(
-                        Type::Trait(Trait::from_id(id, context.db())),
-                        Location::Memory,
-                    )),
+                    // This can only happen when trait methods can implement a default body
+                    Class::Trait(id) => Err(FatalError::new(context.fancy_error(
+                        &format!(
+                            "`{}` is a trait, and can't be used as an expression",
+                            exp.kind
+                        ),
+                        vec![
+                            Label::primary(
+                                id.name_span(context.db()),
+                                &format!("`{}` is defined here as a trait", exp.kind),
+                            ),
+                            Label::primary(
+                                exp.span,
+                                &format!("`{}` is used here as a value", exp.kind),
+                            ),
+                        ],
+                        vec![],
+                    ))),
                     Class::Contract(id) => Ok(ExpressionAttributes::new(
                         Type::SelfContract(Contract::from_id(id, context.db())),
                         Location::Value,
@@ -974,6 +987,14 @@ fn expr_call_named_thing<T: std::fmt::Display>(
                 func.kind
             )],
         ))),
+        NamedThing::Item(Item::Trait(_)) => Err(FatalError::new(context.error(
+            &format!("`{}` is not callable", func.kind),
+            func.span,
+            &format!(
+                "`{}` is a trait, and can't be used as a function",
+                func.kind
+            ),
+        ))),
         NamedThing::Item(Item::Ingot(_)) => Err(FatalError::new(context.error(
             &format!("`{}` is not callable", func.kind),
             func.span,
@@ -1129,11 +1150,7 @@ fn expr_call_type_constructor(
         Type::Struct(struct_type) => {
             return expr_call_struct_constructor(context, name_span, struct_type, args)
         }
-        Type::Base(Base::Bool)
-        | Type::Array(_)
-        | Type::Map(_)
-        | Type::Generic(_)
-        | Type::Trait(_) => {
+        Type::Base(Base::Bool) | Type::Array(_) | Type::Map(_) | Type::Generic(_) => {
             return Err(FatalError::new(context.error(
                 &format!("`{}` type is not callable", typ.name()),
                 name_span,
@@ -1220,7 +1237,6 @@ fn expr_call_type_constructor(
         Type::Struct(_) => unreachable!(),        // handled above
         Type::Map(_) => unreachable!(),           // handled above
         Type::Array(_) => unreachable!(),         // handled above
-        Type::Trait(_) => unreachable!(),         // handled above
         Type::Generic(_) => unreachable!(),       // handled above
         Type::SelfContract(_) => unreachable!(),  /* unnameable; contract names all become
                                                     * Type::Contract */