generation of real benchmark functions for benchmarking v2 (#13224)

* function generation with _name working, need to modify signature

* WIP

* support custom BenchmarkResult<T> type

* full support for BenchmarkResult<T> on benchmark function defs

* support () return type for benchmark function defs that don't use ?

* uncomment

* fix where clause handling

* fix benchmark function call bodies

* proper parsing of return type

* add UI tests for bad return type

* fix detection of missing last_stmt with defined return type

* UI tests covering missing last_stmt

* properly detect and complain about empty benchmark function defs

* fix missing Comma in Result<T, BenchmarkError> parsing + test

* add additional UI test

* allow complex path for BenchmarkResult and BenchmarkError in fn defs

* add UI tests covering complex path for BenchmarkResult, BenchmarkError

* retain doc comments and attributes

* also add attributes to struct

* add docs for benchmark function definition support

* fix imports on benchmark example

* fix issue with unused variables in extrinsic call fn def

* fix up docs

* remove support for v2::BenchmarkResult because it was confusing

* fix typo

* remove ability to use custom T for Result<T, BenchmarkError> in v2

* use missing call error instead of empty_fn()

* remove unneeded match statement

* Add a proper QED

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

* fix other QED

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

* cargo fmt

* add an explicit error for non TypePath as return type

* tweak error warning and add a UI test for non TypePath return

* remove comment

* add docs about T and I generic params

* improve docs referring to section "below"

* pull out return type checking logic into its own function

* pull out params parsing into its own function

* pull out call_def parsing into its own function

* add doc comment for missing_call()

* replace spaces with tabs

* add a result-based example to the benchmarking examples

---------

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

substrate/frame/support/test/tests/benchmark_ui/pass/valid_complex_path_benchmark_result.rs

@@ -0,0 +1,17 @@
+use frame_benchmarking::v2::*;
+#[allow(unused_imports)]
+use frame_support_test::Config;
+
+#[benchmarks]
+mod benches {
+	use super::*;
+
+	#[benchmark]
+	fn bench() -> Result<(), frame_benchmarking::v2::BenchmarkError> {
+		#[block]
+		{}
+		Ok(())
+	}
+}
+
+fn main() {}

substrate/frame/support/test/tests/benchmark_ui/pass/valid_no_last_stmt.rs

@@ -0,0 +1,16 @@
+use frame_benchmarking::v2::*;
+#[allow(unused_imports)]
+use frame_support_test::Config;
+
+#[benchmarks]
+mod benches {
+	use super::*;
+
+	#[benchmark]
+	fn bench() {
+		#[block]
+		{}
+	}
+}
+
+fn main() {}

substrate/frame/support/test/tests/benchmark_ui/pass/valid_path_result_benchmark_error.rs

@@ -0,0 +1,17 @@
+use frame_benchmarking::v2::*;
+#[allow(unused_imports)]
+use frame_support_test::Config;
+
+#[benchmarks]
+mod benches {
+	use super::*;
+
+	#[benchmark]
+	fn bench() -> Result<(), frame_benchmarking::v2::BenchmarkError> {
+		#[block]
+		{}
+		Ok(())
+	}
+}
+
+fn main() {}

substrate/frame/support/test/tests/benchmark_ui/pass/valid_result.rs

@@ -0,0 +1,18 @@
+use frame_benchmarking::v2::*;
+use frame_support_test::Config;
+
+#[benchmarks]
+mod benches {
+	use super::*;
+
+	#[benchmark]
+	fn bench() -> Result<(), BenchmarkError> {
+		let a = 2 + 2;
+		#[block]
+		{}
+		assert_eq!(a, 4);
+		Ok(())
+	}
+}
+
+fn main() {}