[lang2/macro] add ui test for storage-impl conflict

lang2/macro/tests/compile_tests.rs

@@ -39,4 +39,5 @@ fn compile_tests() {
     t.compile_fail("tests/ui/fail/13-abi-constructor.rs");
     t.compile_fail("tests/ui/fail/14-missing-storage-struct.rs");
     t.compile_fail("tests/ui/fail/15-multiple-storage-structs.rs");
+    t.compile_fail("tests/ui/fail/16-storage-impl-ident-conflict.rs");
 }

lang2/macro/tests/ui/fail/16-storage-impl-ident-conflict.rs

+#![feature(proc_macro_hygiene)]
+
+use ink_lang2 as ink;
+
+#[ink::contract(version = "0.1.0")]
+mod noop {
+    // This test ensures that ink! impl blocks are always
+    // implemented on the only storage struct definition.
+
+    #[ink(storage)]
+    struct StorageStruct {}
+
+    // This ink! impl block is okay.
+    impl StorageStruct {
+        #[ink(constructor)]
+        fn new1(&mut self) {}
+
+        #[ink(message)]
+        fn do_something1(&self) {}
+    }
+
+    // Missing the #[ink(storage)] attribute on purpose.
+    struct NonStorageStruct {}
+
+    // This ink! impl block is invalid in that it implement
+    // the messages and constructors for a non-existing ink!
+    // storage struct. We expect a failure here.
+    impl NonStorageStruct {
+        #[ink(constructor)]
+        fn new2(&mut self) {}
+
+        #[ink(message)]
+        fn do_something2(&self) {}
+    }
+}
+
+fn main() {}