Warn on missing pallet::call_index (#12894)

* Warn on missing call_index

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Suppress camel case warning

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Simplify code

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Disallow warnings in pallet-ui tests

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Add pallet UI test

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Update Pallet UI

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* fmt

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Use module instead of function

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Update pallet-ui

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/support/procedural/src/pallet/parse/call.rs

@@ -59,6 +59,8 @@ pub struct CallVariantDef {
 	pub weight: syn::Expr,
 	/// Call index of the dispatchable.
 	pub call_index: u8,
+	/// Whether an explicit call index was specified.
+	pub explicit_call_index: bool,
 	/// Docs, used for metadata.
 	pub docs: Vec<syn::Lit>,
 	/// Attributes annotated at the top of the dispatchable function.
@@ -243,6 +245,7 @@ impl CallDef {
 					FunctionAttr::CallIndex(idx) => idx,
 					_ => unreachable!("checked during creation of the let binding"),
 				});
+				let explicit_call_index = call_index.is_some();
 
 				let final_index = match call_index {
 					Some(i) => i,
@@ -296,6 +299,7 @@ impl CallDef {
 					name: method.sig.ident.clone(),
 					weight,
 					call_index: final_index,
+					explicit_call_index,
 					args,
 					docs,
 					attrs: method.attrs.clone(),