fix: allow calling a trait method with paths that don't consist of ex…

…actly two segments (#5577)

# Description

## Problem

Resolves #5557

## Summary

For something like `Add::add` the logic was checking if `Add` was a
trait, then looking for a method `add` in it. It only worked if the path
had exactly two segments.

I initially thought the fix was simple: also make it work if there are
more segments. However, it got tricky if there's just one segment: we
need to find out the trait associated with the found function. This
wasn't tracked in `FuncMeta` (well, there was a boolean for it but not
the optional `TraitId`) so in this PR this information is now tracked,
and the lookup works in all cases.

## Additional Context

None.

## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_frontend/src/elaborator/mod.rs

@@ -647,7 +647,7 @@ impl<'context> Elaborator<'context> {
         &mut self,
         func: &mut NoirFunction,
         func_id: FuncId,
-        is_trait_function: bool,
+        trait_id: Option<TraitId>,
     ) {
         let in_contract = if self.self_type.is_some() {
             // Without this, impl methods can accidentally be placed in contracts.
@@ -761,6 +761,7 @@ impl<'context> Elaborator<'context> {
             direct_generics,
             all_generics: self.generics.clone(),
             struct_id,
+            trait_id,
             trait_impl: self.current_trait_impl,
             parameters: parameters.into(),
             parameter_idents,
@@ -769,7 +770,6 @@ impl<'context> Elaborator<'context> {
             has_body: !func.def.body.is_empty(),
             trait_constraints,
             is_entry_point,
-            is_trait_function,
             has_inline_attribute,
             source_crate: self.crate_id,
             source_module: self.local_module,
@@ -1467,7 +1467,7 @@ impl<'context> Elaborator<'context> {
         for (local_module, id, func) in &mut function_set.functions {
             self.local_module = *local_module;
             self.recover_generics(|this| {
-                this.define_function_meta(func, *id, false);
+                this.define_function_meta(func, *id, None);
             });
         }
     }

compiler/noirc_frontend/src/elaborator/trait_impls.rs

@@ -61,7 +61,7 @@ impl<'context> Elaborator<'context> {
                     let module = self.module_id();
                     let location = Location::new(default_impl.def.span, trait_impl.file_id);
                     self.interner.push_function(func_id, &default_impl.def, module, location);
-                    self.define_function_meta(&mut default_impl_clone, func_id, false);
+                    self.define_function_meta(&mut default_impl_clone, func_id, None);
                     func_ids_in_trait.insert(func_id);
                     ordered_methods.push((
                         method.default_impl_module_id,

compiler/noirc_frontend/src/elaborator/traits.rs

@@ -123,6 +123,7 @@ impl<'context> Elaborator<'context> {
                     let func_id = unresolved_trait.method_ids[&name.0.contents];
 
                     this.resolve_trait_function(
+                        trait_id,
                         name,
                         generics,
                         parameters,
@@ -171,8 +172,10 @@ impl<'context> Elaborator<'context> {
         functions
     }
 
+    #[allow(clippy::too_many_arguments)]
     pub fn resolve_trait_function(
         &mut self,
+        trait_id: TraitId,
         name: &Ident,
         generics: &UnresolvedGenerics,
         parameters: &[(Ident, UnresolvedType)],
@@ -206,7 +209,7 @@ impl<'context> Elaborator<'context> {
         };
 
         let mut function = NoirFunction { kind, def };
-        self.define_function_meta(&mut function, func_id, true);
+        self.define_function_meta(&mut function, func_id, Some(trait_id));
         self.elaborate_function(func_id);
         let _ = self.scopes.end_function();
         // Don't check the scope tree for unused variables, they can't be used in a declaration anyway.

compiler/noirc_frontend/src/elaborator/types.rs

@@ -28,7 +28,8 @@ use crate::{
         Signedness, UnaryOp, UnresolvedType, UnresolvedTypeData,
     },
     node_interner::{
-        DefinitionKind, DependencyId, ExprId, GlobalId, TraitId, TraitImplKind, TraitMethodId,
+        DefinitionKind, DependencyId, ExprId, FuncId, GlobalId, TraitId, TraitImplKind,
+        TraitMethodId,
     },
     Generics, Kind, ResolvedGeneric, Type, TypeBinding, TypeVariable, TypeVariableKind,
 };
@@ -444,29 +445,20 @@ impl<'context> Elaborator<'context> {
         &mut self,
         path: &Path,
     ) -> Option<(TraitMethodId, TraitConstraint, bool)> {
-        if path.kind == PathKind::Plain && path.segments.len() == 2 {
-            let method = &path.segments[1];
-
-            let mut trait_path = path.clone();
-            trait_path.pop();
-            let trait_id = self.lookup(trait_path).ok()?;
-            let the_trait = self.interner.get_trait(trait_id);
-
-            let method = the_trait.find_method(method.0.contents.as_str())?;
-            let constraint = TraitConstraint {
-                typ: Type::TypeVariable(
-                    the_trait.self_type_typevar.clone(),
-                    TypeVariableKind::Normal,
-                ),
-                trait_generics: Type::from_generics(&vecmap(&the_trait.generics, |generic| {
-                    generic.type_var.clone()
-                })),
-                trait_id,
-                span: path.span(),
-            };
-            return Some((method, constraint, false));
-        }
-        None
+        let func_id: FuncId = self.lookup(path.clone()).ok()?;
+        let meta = self.interner.function_meta(&func_id);
+        let trait_id = meta.trait_id?;
+        let the_trait = self.interner.get_trait(trait_id);
+        let method = the_trait.find_method(&path.last_segment().0.contents)?;
+        let constraint = TraitConstraint {
+            typ: Type::TypeVariable(the_trait.self_type_typevar.clone(), TypeVariableKind::Normal),
+            trait_generics: Type::from_generics(&vecmap(&the_trait.generics, |generic| {
+                generic.type_var.clone()
+            })),
+            trait_id,
+            span: path.span(),
+        };
+        Some((method, constraint, false))
     }
 
     // This resolves a static trait method T::trait_method by iterating over the where clause

compiler/noirc_frontend/src/hir_def/function.rs

@@ -8,7 +8,7 @@ use crate::ast::{FunctionKind, FunctionReturnType, Visibility};
 use crate::graph::CrateId;
 use crate::hir::def_map::LocalModuleId;
 use crate::macros_api::{BlockExpression, StructId};
-use crate::node_interner::{ExprId, NodeInterner, TraitImplId};
+use crate::node_interner::{ExprId, NodeInterner, TraitId, TraitImplId};
 use crate::{ResolvedGeneric, Type};
 
 /// A Hir function is a block expression with a list of statements.
@@ -134,18 +134,16 @@ pub struct FuncMeta {
     /// The struct this function belongs to, if any
     pub struct_id: Option<StructId>,
 
+    // The trait this function belongs to, if any
+    pub trait_id: Option<TraitId>,
+
     /// The trait impl this function belongs to, if any
     pub trait_impl: Option<TraitImplId>,
 
     /// True if this function is an entry point to the program.
     /// For non-contracts, this means the function is `main`.
     pub is_entry_point: bool,
 
-    /// True if this function was defined within a trait (not a trait impl!).
-    /// Trait functions are just stubs and shouldn't have their return type checked
-    /// against their body type, nor should unused variables be checked.
-    pub is_trait_function: bool,
-
     /// True if this function is marked with an attribute
     /// that indicates it should be inlined differently than the default (inline everything).
     /// For example, such as `fold` (never inlined) or `no_predicates` (inlined after flattening)
@@ -174,7 +172,7 @@ impl FuncMeta {
     /// We don't check the return type of these functions since it will always have
     /// an empty body, and we don't check for unused parameters.
     pub fn is_stub(&self) -> bool {
-        self.kind.can_ignore_return_type() || self.is_trait_function
+        self.kind.can_ignore_return_type() || self.trait_id.is_some()
     }
 
     pub fn function_signature(&self) -> FunctionSignature {

test_programs/compile_success_empty/trait_call_full_path/Nargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "trait_call_full_path"
+type = "bin"
+authors = [""]
+
+[dependencies]

test_programs/compile_success_empty/trait_call_full_path/src/main.nr

@@ -0,0 +1,20 @@
+mod foo {
+    trait Trait {
+        fn me(self) -> Self;
+    }
+
+    impl Trait for Field {
+        fn me(self) -> Self {
+            self
+        }
+    }
+}
+
+use foo::Trait;
+use foo::Trait::me;
+
+fn main(x: Field) {
+    let _ = foo::Trait::me(x);
+    let _ = Trait::me(x);
+    let _ = me(x);
+}