fix: Improve member access error (noir-lang#940)

* Improve member access error * Fix broken error * cargo fmt * Feedback
ax0 · Mar 10, 2023 · 9b5b5f6 · 9b5b5f6
1 parent 2ee0119
commit 9b5b5f6
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Showing 2 changed files with 14 additions and 2 deletions.
diff --git 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
@@ -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),