don't crash on unbound name in match star pattern

Reviewed By: migeed-z

Differential Revision: D88674472

fbshipit-source-id: d2d8d152169e1de1a810ec39d966db6e81f11f2e

Author: yangdanny97

pyrefly/lib/binding/pattern.rs

@@ -333,7 +333,12 @@ impl<'a> BindingsBuilder<'a> {
                 self.finish_match_or_fork();
                 narrow_ops.unwrap_or_default()
             }
-            Pattern::MatchStar(_) => NarrowOps::new(),
+            Pattern::MatchStar(p) => {
+                if let Some(name) = &p.name {
+                    self.bind_definition(name, Binding::Forward(subject_idx), FlowStyle::Other);
+                }
+                NarrowOps::new()
+            }
         }
     }
 

pyrefly/lib/test/flow_branching.rs

@@ -721,7 +721,7 @@ match x:
 );
 
 testcase!(
-    test_crashing_match,
+    test_crashing_match_sequence,
     r#"
 match []:
     case [[1]]:
@@ -731,6 +731,19 @@ match []:
 "#,
 );
 
+testcase!(
+    test_crashing_match_star,
+    r#"
+match []:
+    case *x: # E: Parse error: Star pattern cannot be used here
+        pass
+    case *x | 1: # E: Parse error: Star pattern cannot be used here # E: alternative patterns bind different names
+        pass
+    case 1 | *x: # E: Parse error: Star pattern cannot be used here # E: alternative patterns bind different names
+        pass
+"#,
+);
+
 testcase!(
     test_match_narrow_generic,
     r#"