Avoid inferring types for invalid binary expressions in string annotations

crates/ty_python_semantic/resources/mdtest/annotations/string.md

@@ -156,6 +156,9 @@ a: "1 or 2"
 b: "(x := 1)"
 # error: [invalid-type-form]
 c: "1 + 2"
+# Regression test for https://github.com/astral-sh/ty/issues/1847
+# error: [invalid-type-form]
+c2: "a*(i for i in [])"
 d: "lambda x: x"
 e: "x if True else y"
 f: "{'a': 1, 'b': 2}"

crates/ty_python_semantic/src/types/infer/builder/type_expression.rs

@@ -155,7 +155,12 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
                     }
                     // anything else is an invalid annotation:
                     op => {
-                        self.infer_binary_expression(binary, TypeContext::default());
+                        // Avoid inferring the types of invalid binary expressions that have been
+                        // parsed from a string annotation, as they are not present in the semantic
+                        // index.
+                        if !self.deferred_state.in_string_annotation() {
+                            self.infer_binary_expression(binary, TypeContext::default());
+                        }
                         self.report_invalid_type_expression(
                             expression,
                             format_args!(