add minimized test for issue rust-lang#116539

Author: drahnr

tests/rustdoc/issue-116539.rs

@@ -0,0 +1,24 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/116539>.
+#![no_std]
+#![crate_name = "foo"]
+
+trait IdentifyAccount {
+    type A;
+}
+struct RealSigner {}
+
+impl IdentifyAccount for RealSigner {
+    type A = u32;
+}
+
+type RealAccountId = <RealSigner as IdentifyAccount>::A;
+
+trait BaseConfig {
+    type B;
+}
+
+trait Config: BaseConfig<B = RealAccountId> {}
+
+struct GenesisConfig<T: Config> {
+    shelves: [<T as BaseConfig>::B; 2],
+}