chore: enhance trait constraint comment

compiler/noirc_frontend/src/elaborator/patterns.rs

@@ -1035,16 +1035,21 @@ impl Elaborator<'_> {
         //     fn new() -> Self;
         // }
         //
-        // fn foo<O: One, T: Two<O>>() {
+        // fn foo<X: One, T: Two<X>>() {
         //     let _: T = Two::new();
         // }
         // ```
         //
         // when type-checking `Two::new` we'll have a return type `'2` which is constrained by `'2: Two<'1>`.
         // Then the definition for `new` has a constraint on it, `O: One`, which translates to `'1: One`.
         //
-        // If we try to find a trait implementation for `'1` before finding one for `'2` we'll never find it:
-        // once we find one for `'2`, `'1` will become bound and a trait implementation will be found.
+        // Because of the explicit type in the `let`, `'2` will be unified with `T`.
+        // Then we must first verify the constraint `'2: Two<'1>`, which is now `T: Two<'1>`, to find
+        // that the implementation is the assumed one `T: Two<X>` so that `'1` is bound to `X`.
+        // Then we can successfully verify the constraint `'1: One` which now became `X: One` which holds
+        // because of the assumed constraint.
+        //
+        // If we try to find a trait implementation for `'1` before finding one for `'2` we'll never find it.
         if let Some(definition) = self.interner.try_definition(ident.id) {
             if let DefinitionKind::Function(function) = definition.kind {
                 let function = self.interner.function_meta(&function);