[ty] Short circuit ReachabilityConstraints::analyze_single for dynamic types (#19867)

Author: MichaReiser

crates/ty_python_semantic/resources/mdtest/function/return_type.md

@@ -505,3 +505,16 @@ class Abstract(Protocol):
 class Concrete(Abstract):
     def method(self) -> str: ...  # error: [invalid-return-type]
 ```
+
+## Diagnostics for `invalid-return-type` on dynamic type
+
+```toml
+environment.python-version = "3.12"
+```
+
+```py
+from typing import Never, Any
+
+def f(func: Any) -> Never:  # error: [invalid-return-type]
+    func()
+```

crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs

@@ -815,6 +815,17 @@ impl ReachabilityConstraints {
                 // very large in number, since we add them on all statement level function calls.
                 let ty = infer_expression_type(db, callable);
 
+                // Short-circuit for well known types that are known not to return `Never` when called.
+                // Without the short-circuit, we've seen that threads keep blocking each other
+                // because they all try to acquire Salsa's `CallableType` lock that ensures each type
+                // is only interned once. The lock is so heavily congested because there are only
+                // very few dynamic types, in which case Salsa's sharding the locks by value
+                // doesn't help much.
+                // See <https://github.com/astral-sh/ty/issues/968>.
+                if matches!(ty, Type::Dynamic(_)) {
+                    return Truthiness::AlwaysFalse.negate_if(!predicate.is_positive);
+                }
+
                 let overloads_iterator =
                     if let Some(Type::Callable(callable)) = ty.into_callable(db) {
                         callable.signatures(db).overloads.iter()