Ensure inherent are first (#8173)

* impl

* fix tests

* impl in execute_block

* fix tests

* add a test in frame-executive

* fix some panic warning

* use trait to get call from extrinsic

* remove unused

* fix test

* fix testing

* fix tests

* return index of extrinsic on error

* fix test

* Update primitives/inherents/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* address comments

rename trait, and refactor

* refactor + doc improvment

* fix tests

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

substrate/frame/support/src/traits/misc.rs

@@ -284,3 +284,40 @@ pub trait GetBacking {
 	/// implicit motion. `None` if it does not.
 	fn get_backing(&self) -> Option<Backing>;
 }
+
+
+
+/// A trait to ensure the inherent are before non-inherent in a block.
+///
+/// This is typically implemented on runtime, through `construct_runtime!`.
+pub trait EnsureInherentsAreFirst<Block> {
+	/// Ensure the position of inherent is correct, i.e. they are before non-inherents.
+	///
+	/// On error return the index of the inherent with invalid position (counting from 0).
+	fn ensure_inherents_are_first(block: &Block) -> Result<(), u32>;
+}
+
+/// An extrinsic on which we can get access to call.
+pub trait ExtrinsicCall: sp_runtime::traits::Extrinsic {
+	/// Get the call of the extrinsic.
+	fn call(&self) -> &Self::Call;
+}
+
+#[cfg(feature = "std")]
+impl<Call, Extra> ExtrinsicCall for sp_runtime::testing::TestXt<Call, Extra> where
+	Call: codec::Codec + Sync + Send,
+{
+	fn call(&self) -> &Self::Call {
+		&self.call
+	}
+}
+
+impl<Address, Call, Signature, Extra> ExtrinsicCall
+for sp_runtime::generic::UncheckedExtrinsic<Address, Call, Signature, Extra>
+where
+	Extra: sp_runtime::traits::SignedExtension,
+{
+	fn call(&self) -> &Self::Call {
+		&self.function
+	}
+}