[test] Add crasher for #84884

Author: AnthonyLatsis

validation-test/compiler_crashers_2/a956308a078fc27f.swift

@@ -0,0 +1,32 @@
+// https://github.com/swiftlang/swift/issues/84884
+// RUN: not --crash %target-swift-frontend -typecheck %s
+
+protocol Proto<Assoc> {
+  associatedtype Assoc
+}
+
+struct Generic<Assoc>: Proto {
+  static func foo(_: Generic<Assoc>) -> Generic<Assoc> {}
+  static func bar(_: some Proto<Assoc>) -> Generic<Assoc> {}
+}
+
+struct S1 {}
+struct S2 {}
+
+extension Proto {
+  func overload() -> some Proto<S1> where Assoc == S1 {
+    Generic()
+  }
+  func overload() -> some Proto<S1> where Assoc == Generic<Generic<S1>> {
+    Generic()
+  }
+}
+
+struct Struct: Proto {
+  typealias Assoc = Generic<Generic<S2>>
+  init(_: Int) {}
+}
+
+func test() {
+  let _ = Generic.foo(Generic.bar(Struct(0).overload())
+}