[panic] `Callable` type annotations cannot be overloaded

[NorthLake]

Summary

I use ty's LSP through the RyeCharm plugin in Pycharm. I don't have a config file set. These are the settings I used in RyeCharm:

Reproduction example:

def apply_formatting(string: str, case_style: Literal["upper", "lower", "title"]) -> str:
    case_map = {
        "upper": str.upper,
        "lower": str.lower,
        "title": str.title,
    }
    return case_map.get(case_style, lambda x: x)(string)

Error output:

Panicked at crates\ty_python_semantic\src\types\infer\builder.rs:6455:17 when checking `c:\[...].py`: ``Callable` type annotations cannot be overloaded`

info: This indicates a bug in ty.
info: If you could open an issue at https://github.com/astral-sh/ty/issues/new?title=%5Bpanic%5D, we'd be very appreciative!
info: Platform: windows x86_64 info: Version: 0.0.30 (12e86b58b 2026-04-14)
info: Args: ["C:\\[...]\\ty.exe", "server"]
info: Backtrace:
0:
[1-31]:
32:
33: BaseThreadInitThunk
34: RtlUserThreadStart

info: query stacktrace:
0: infer_scope_types_impl(Id(1b86))
at crates\ty_python_semantic\src\types\infer.rs:263
1: check_file_impl(Id(149d))
at crates\ty_project\src\lib.rs:616

Version

ty 0.0.30 (12e86b5 2026-04-14)

[NorthLake]

Figured I should probably try it myself as well, and running ty check gives basically the same output

[charliermarsh]

Thanks for filing, we'll take a look!

[charliermarsh]

\cc @ibraheemdev

[charliermarsh]

The minimal fix is:

diff --git a/crates/ty_python_semantic/src/types/infer/builder.rs b/crates/ty_python_semantic/src/types/infer/builder.rs
index e64733bbb0..24b8ece63f 100644
--- a/crates/ty_python_semantic/src/types/infer/builder.rs
+++ b/crates/ty_python_semantic/src/types/infer/builder.rs
@@ -6452,11 +6452,12 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 .filter_union(self.db(), Type::is_callable_type)
                 .as_callable()
         {
-            let [signature] = callable.signatures(self.db()).overloads.as_slice() else {
-                panic!("`Callable` type annotations cannot be overloaded");
-            };
-
-            Some(signature)
+            match callable.signatures(self.db()).overloads.as_slice() {
+                [signature] => Some(signature),
+                // We don't yet support multi-inference for lambdas with overloaded callable type
+                // context, so fall back to ordinary inference instead of panicking.
+                _ => None,
+            }
         } else {
             None
         };