[TypeChecker] NFC: Add a test-case for issue#59031 (crash in ConjunctionStep::resume)

Author: xedin

validation-test/Sema/type_checker_crashers_fixed/issue59031.swift

@@ -0,0 +1,21 @@
+// RUN: not %target-swift-frontend %s -typecheck
+
+struct Data {
+  // Type `Q` not declared yet.
+  typealias ReturnType = Q
+
+  mutating func withContiguousMutableStorageIfAvailable<R>(
+    _ body: ()  -> R
+    // If you put "R" instead of "ReturnType", it doesn't crash.
+  ) -> ReturnType {
+    fatalError()
+  }
+}
+
+func withUnsafeMutableBufferPointer<R>() -> R {
+  var data = Data()
+  return data.withContiguousMutableStorageIfAvailable {
+    _ = Int.init
+    return 2 as Any as R
+  }
+}