decl_module! print better error on duplicate reserved keyword (#6384)

* `decl_module!` print better error on duplicate reserved keyword

This prints a better error message on duplicated reserved keywords,
instead of complaining because of missing `origin`.

* Review feedback

substrate/frame/support/test/tests/decl_module_ui.rs

@@ -0,0 +1,26 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2020 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//#[rustversion::attr(not(stable), ignore)]
+#[test]
+fn decl_module_ui() {
+	// As trybuild is using `cargo check`, we don't need the real WASM binaries.
+	std::env::set_var("BUILD_DUMMY_WASM_BINARY", "1");
+
+	let t = trybuild::TestCases::new();
+	t.compile_fail("tests/decl_module_ui/*.rs");
+}

substrate/frame/support/test/tests/decl_module_ui/reserved_keyword_two_times_integrity_test.rs

@@ -0,0 +1,7 @@
+frame_support::decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		fn integrity_test() {}
+
+		fn integrity_test() {}
+	}
+}

substrate/frame/support/test/tests/decl_module_ui/reserved_keyword_two_times_integrity_test.stderr

@@ -0,0 +1,25 @@
+error: `integrity_test` can only be passed once as input.
+ --> $DIR/reserved_keyword_two_times_integrity_test.rs:1:1
+  |
+1 | / frame_support::decl_module! {
+2 | |     pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+3 | |         fn integrity_test() {}
+4 | |
+5 | |         fn integrity_test() {}
+6 | |     }
+7 | | }
+  | |_^
+  |
+  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0601]: `main` function not found in crate `$CRATE`
+ --> $DIR/reserved_keyword_two_times_integrity_test.rs:1:1
+  |
+1 | / frame_support::decl_module! {
+2 | |     pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+3 | |         fn integrity_test() {}
+4 | |
+5 | |         fn integrity_test() {}
+6 | |     }
+7 | | }
+  | |_^ consider adding a `main` function to `$DIR/tests/decl_module_ui/reserved_keyword_two_times_integrity_test.rs`

substrate/frame/support/test/tests/decl_module_ui/reserved_keyword_two_times_on_initialize.rs

@@ -0,0 +1,11 @@
+frame_support::decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		fn on_initialize() -> Weight {
+			0
+		}
+
+		fn on_initialize() -> Weight {
+			0
+		}
+	}
+}

substrate/frame/support/test/tests/decl_module_ui/reserved_keyword_two_times_on_initialize.stderr

@@ -0,0 +1,25 @@
+error: `on_initialize` can only be passed once as input.
+  --> $DIR/reserved_keyword_two_times_on_initialize.rs:1:1
+   |
+1  | / frame_support::decl_module! {
+2  | |     pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+3  | |         fn on_initialize() -> Weight {
+4  | |             0
+...  |
+10 | |     }
+11 | | }
+   | |_^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0601]: `main` function not found in crate `$CRATE`
+  --> $DIR/reserved_keyword_two_times_on_initialize.rs:1:1
+   |
+1  | / frame_support::decl_module! {
+2  | |     pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+3  | |         fn on_initialize() -> Weight {
+4  | |             0
+...  |
+10 | |     }
+11 | | }
+   | |_^ consider adding a `main` function to `$DIR/tests/decl_module_ui/reserved_keyword_two_times_on_initialize.rs`