From 9b5b5f6ba8830f1c7d0eb46b0888f15f9fe6b5d7 Mon Sep 17 00:00:00 2001
From: jfecher <jake@aztecprotocol.com>
Date: Fri, 10 Mar 2023 04:42:18 -0600
Subject: [PATCH] fix: Improve member access error (#940)

* Improve member access error

* Fix broken error

* cargo fmt

* Feedback
---
 crates/noirc_frontend/src/hir/type_check/errors.rs | 7 +++++++
 crates/noirc_frontend/src/hir/type_check/expr.rs   | 9 +++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/crates/noirc_frontend/src/hir/type_check/errors.rs b/crates/noirc_frontend/src/hir/type_check/errors.rs
index 33e98e3d6af..5e35d30d22c 100644
--- a/crates/noirc_frontend/src/hir/type_check/errors.rs
+++ b/crates/noirc_frontend/src/hir/type_check/errors.rs
@@ -32,6 +32,8 @@ pub enum TypeCheckError {
         second_type: String,
         second_index: usize,
     },
+    #[error("Cannot infer type of expression, type annotations needed before this point")]
+    TypeAnnotationsNeeded { span: Span },
 }
 
 impl TypeCheckError {
@@ -96,6 +98,11 @@ impl From<TypeCheckError> for Diagnostic {
                 format!("return type is {typ}"),
                 span,
             ),
+            TypeCheckError::TypeAnnotationsNeeded { span } => Diagnostic::simple_error(
+                "Expression type is ambiguous".to_string(),
+                "Type must be known at this point".to_string(),
+                span,
+            ),
         }
     }
 }
diff --git a/crates/noirc_frontend/src/hir/type_check/expr.rs b/crates/noirc_frontend/src/hir/type_check/expr.rs
index 4f5ddbca9d8..48ba39d980f 100644
--- a/crates/noirc_frontend/src/hir/type_check/expr.rs
+++ b/crates/noirc_frontend/src/hir/type_check/expr.rs
@@ -695,7 +695,7 @@ pub fn check_member_access(
     expr_id: ExprId,
     errors: &mut Vec<TypeCheckError>,
 ) -> Type {
-    let lhs_type = type_check_expression(interner, &access.lhs, errors);
+    let lhs_type = type_check_expression(interner, &access.lhs, errors).follow_bindings();
 
     if let Type::Struct(s, args) = &lhs_type {
         let s = s.borrow();
@@ -712,7 +712,12 @@ pub fn check_member_access(
         }
     }
 
-    if lhs_type != Type::Error {
+    // If we get here the type has no field named 'access.rhs'.
+    // Now we specialize the error message based on whether we know the object type in question yet.
+    if let Type::TypeVariable(..) = &lhs_type {
+        errors
+            .push(TypeCheckError::TypeAnnotationsNeeded { span: interner.expr_span(&access.lhs) });
+    } else if lhs_type != Type::Error {
         errors.push(TypeCheckError::Unstructured {
             msg: format!("Type {lhs_type} has no member named {}", access.rhs),
             span: interner.expr_span(&access.lhs),