Improve mock_impl_runtime_apis! (#7370)

* Improve `mock_impl_runtime_apis!`

This adds a new attribute for functions being implemented in the
`mock_impl_runtime_apis!` macro, the `advanced` attribute. When this
attribute is given the user gets access to the `at` parameter and is
able to return a `Result`, instead of letting the macro generate this
stuff.

* Use the `at_param_name` directly

* Prevent clashing of `params`

substrate/primitives/api/test/tests/ui/mock_advanced_block_id_by_value.rs

@@ -0,0 +1,20 @@
+use substrate_test_runtime_client::runtime::Block;
+
+sp_api::decl_runtime_apis! {
+	pub trait Api {
+		fn test();
+	}
+}
+
+struct MockApi;
+
+sp_api::mock_impl_runtime_apis! {
+	impl Api<Block> for MockApi {
+		#[advanced]
+		fn test(&self, _: BlockId<Block>) -> Result<sp_core::NativeOrEncoded<()>, String> {
+			Ok(().into())
+		}
+	}
+}
+
+fn main() {}

substrate/primitives/api/test/tests/ui/mock_advanced_block_id_by_value.stderr

@@ -0,0 +1,13 @@
+error: `BlockId` needs to be taken by reference and not by value!
+  --> $DIR/mock_advanced_block_id_by_value.rs:11:1
+   |
+11 | / sp_api::mock_impl_runtime_apis! {
+12 | |     impl Api<Block> for MockApi {
+13 | |         #[advanced]
+14 | |         fn test(&self, _: BlockId<Block>) -> Result<sp_core::NativeOrEncoded<()>, String> {
+...  |
+17 | |     }
+18 | | }
+   | |_^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

substrate/primitives/api/test/tests/ui/mock_advanced_missing_blockid.rs

@@ -0,0 +1,20 @@
+use substrate_test_runtime_client::runtime::Block;
+
+sp_api::decl_runtime_apis! {
+	pub trait Api {
+		fn test();
+	}
+}
+
+struct MockApi;
+
+sp_api::mock_impl_runtime_apis! {
+	impl Api<Block> for MockApi {
+		#[advanced]
+		fn test(&self) -> Result<sp_core::NativeOrEncoded<()>, String> {
+			Ok(().into())
+		}
+	}
+}
+
+fn main() {}

substrate/primitives/api/test/tests/ui/mock_advanced_missing_blockid.stderr

@@ -0,0 +1,5 @@
+error: If using the `advanced` attribute, it is required that the function takes at least one argument, the `BlockId`.
+  --> $DIR/mock_advanced_missing_blockid.rs:14:3
+   |
+14 |         fn test(&self) -> Result<sp_core::NativeOrEncoded<()>, String> {
+   |         ^^

substrate/primitives/api/test/tests/ui/mock_only_one_error_type.stderr

@@ -4,22 +4,22 @@ error: Error type can not change between runtime apis
 23 |         type Error = u64;
    |         ^^^^
 
+error: First error type was declared here.
+  --> $DIR/mock_only_one_error_type.rs:17:16
+   |
+17 |         type Error = u32;
+   |                      ^^^
+
 error[E0277]: the trait bound `u32: std::convert::From<std::string::String>` is not satisfied
-   --> $DIR/mock_only_one_error_type.rs:15:1
+   --> $DIR/mock_only_one_error_type.rs:17:16
     |
-15  | / sp_api::mock_impl_runtime_apis! {
-16  | |     impl Api<Block> for MockApi {
-17  | |         type Error = u32;
-18  | |
-...   |
-26  | |     }
-27  | | }
-    | |_^ the trait `std::convert::From<std::string::String>` is not implemented for `u32`
-    | 
-   ::: $WORKSPACE/primitives/api/src/lib.rs:350:35
+17  |         type Error = u32;
+    |                      ^^^ the trait `std::convert::From<std::string::String>` is not implemented for `u32`
     |
-350 |       type Error: std::fmt::Debug + From<String>;
-    |                                     ------------ required by this bound in `sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiErrorExt`
+   ::: $WORKSPACE/primitives/api/src/lib.rs
+    |
+    |     type Error: std::fmt::Debug + From<String>;
+    |                                   ------------ required by this bound in `sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiErrorExt`
     |
     = help: the following implementations were found:
               <u32 as std::convert::From<bool>>
@@ -27,4 +27,3 @@ error[E0277]: the trait bound `u32: std::convert::From<std::string::String>` is
               <u32 as std::convert::From<h2::frame::reason::Reason>>
               <u32 as std::convert::From<h2::frame::reason::Reason>>
             and 18 others
-    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)