Skip attribute suggestions for partial union failures

pyrefly/lib/alt/attr.rs

@@ -545,6 +545,9 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
         let mut error_messages = Vec::new();
         let mut success = true;
         let (found, not_found, error) = lookup_result.decompose();
+        // Check if we have a partial union failure (attribute exists on some union members
+        // but not others) before consuming the vectors. This helps us decide whether to suggest.
+        let is_partial_union_failure = !found.is_empty() && !not_found.is_empty();
         for (attr, _) in found {
             match self.resolve_get_access(attr_name, attr, range, errors, context) {
                 Ok(ty) => types.push(ty),
@@ -571,9 +574,13 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
             error_messages.sort();
             error_messages.dedup();
             let mut msg = vec1![error_messages.join("\n")];
-            if let Some(suggestion) = attr_base
-                .as_ref()
-                .and_then(|attr_base| self.suggest_attribute_name(attr_name, attr_base))
+            // Skip suggestions when we have a partial union failure to avoid suggesting
+            // attributes from the types that have them when the problem is that some types
+            // don't have the attribute at all.
+            if !is_partial_union_failure
+                && let Some(suggestion) = attr_base
+                    .as_ref()
+                    .and_then(|attr_base| self.suggest_attribute_name(attr_name, attr_base))
             {
                 msg.push(format!("Did you mean `{suggestion}`?"));
             }

pyrefly/lib/test/attributes.rs

@@ -2112,6 +2112,68 @@ def f(x: Color) -> Color:
 "#,
 );
 
+testcase!(
+    test_union_attribute_missing_no_suggestion,
+    r#"
+# When an attribute exists on some union members but not others,
+# we shouldn't suggest similar attributes from the types that have it
+def f(x: str | None):
+    return x.split()  # E: Object of class `NoneType` has no attribute `split`
+"#,
+);
+
+testcase!(
+    test_union_attribute_missing_no_suggestion_three_types,
+    r#"
+# Partial union failure with 3 types: attribute exists on 1, missing on 2
+def f(x: str | int | None):
+    return x.split()  # E: Object of class `NoneType` has no attribute `split`\nObject of class `int` has no attribute `split`
+"#,
+);
+
+testcase!(
+    test_union_attribute_missing_no_suggestion_mostly_have_it,
+    r#"
+# Even if most types have the attribute, if ANY don't, skip suggestion
+class A:
+    upper: int
+    lower: int
+class B:
+    upper: int
+    lower: int
+def f(x: str | A | B):
+    # str has "upper" method, A and B have "upper" attribute
+    # But str doesn't have "lower" attribute, A and B do
+    x.lowerr  # E: Object of class `str` has no attribute `lowerr`
+"#,
+);
+
+testcase!(
+    test_union_both_missing_should_suggest,
+    r#"
+# When an attribute is missing on ALL union members, we should still suggest
+class A:
+    value: int
+class B:
+    value: str
+def f(x: A | B):
+    return x.vaule  # E: Object of class `A` has no attribute `vaule`\nObject of class `B` has no attribute `vaule`\n  Did you mean `value`?
+"#,
+);
+
+testcase!(
+    test_union_all_have_attribute_no_error,
+    r#"
+# When all union members have the attribute, there should be no error
+class A:
+    value: int
+class B:
+    value: str
+def f(x: A | B):
+    return x.value  # No error - both A and B have 'value'
+"#,
+);
+
 testcase!(
     test_class_toplevel_inherited_attr_name,
     r#"