add frame_system::DefaultConfig to individual pallet DefaultConfigs (#14453)

* add frame_system::DefaultConfig to individual pallet DefaultConfigs

* Fixes tests

* Minor fix

* ".git/.scripts/commands/fmt/fmt.sh"

* Adds UI Tests

---------

Co-authored-by: Nikhil Gupta <17176722+gupnik@users.noreply.github.com>
Co-authored-by: command-bot <>

substrate/frame/support/procedural/src/pallet/expand/config.rs

@@ -49,24 +49,33 @@ Consequently, a runtime that wants to include this pallet must implement this tr
 	);
 
 	// we only emit `DefaultConfig` if there are trait items, so an empty `DefaultConfig` is
-	// impossible consequently
-	if config.default_sub_trait.len() > 0 {
-		let trait_items = &config.default_sub_trait;
-		quote!(
-			/// Based on [`Config`]. Auto-generated by
-			/// [`#[pallet::config(with_default)]`](`frame_support::pallet_macros::config`).
-			/// Can be used in tandem with
-			/// [`#[register_default_config]`](`frame_support::register_default_config`) and
-			/// [`#[derive_impl]`](`frame_support::derive_impl`) to derive test config traits
-			/// based on existing pallet config traits in a safe and developer-friendly way.
-			///
-			/// See [here](`frame_support::pallet_macros::config`) for more information and caveats about
-			/// the auto-generated `DefaultConfig` trait and how it is generated.
-			pub trait DefaultConfig {
-				#(#trait_items)*
-			}
-		)
-	} else {
-		Default::default()
+	// impossible consequently.
+	match &config.default_sub_trait {
+		Some(default_sub_trait) if default_sub_trait.items.len() > 0 => {
+			let trait_items = &default_sub_trait.items;
+
+			let type_param_bounds = if default_sub_trait.has_system {
+				let system = &def.frame_system;
+				quote::quote!(: #system::DefaultConfig)
+			} else {
+				quote::quote!()
+			};
+
+			quote!(
+				/// Based on [`Config`]. Auto-generated by
+				/// [`#[pallet::config(with_default)]`](`frame_support::pallet_macros::config`).
+				/// Can be used in tandem with
+				/// [`#[register_default_config]`](`frame_support::register_default_config`) and
+				/// [`#[derive_impl]`](`frame_support::derive_impl`) to derive test config traits
+				/// based on existing pallet config traits in a safe and developer-friendly way.
+				///
+				/// See [here](`frame_support::pallet_macros::config`) for more information and caveats about
+				/// the auto-generated `DefaultConfig` trait and how it is generated.
+				pub trait DefaultConfig #type_param_bounds {
+					#(#trait_items)*
+				}
+			)
+		},
+		_ => Default::default(),
 	}
 }

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

@@ -37,6 +37,12 @@ mod keyword {
 	syn::custom_keyword!(constant);
 }
 
+#[derive(Default)]
+pub struct DefaultTrait {
+	pub items: Vec<syn::TraitItem>,
+	pub has_system: bool,
+}
+
 /// Input definition for the pallet config.
 pub struct ConfigDef {
 	/// The index of item in pallet module.
@@ -58,8 +64,8 @@ pub struct ConfigDef {
 	///
 	/// Contains default sub-trait items (instantiated by `#[pallet::config(with_default)]`).
 	/// Vec will be empty if `#[pallet::config(with_default)]` is not specified or if there are
-	/// no trait items
-	pub default_sub_trait: Vec<syn::TraitItem>,
+	/// no trait items.
+	pub default_sub_trait: Option<DefaultTrait>,
 }
 
 /// Input definition for a constant in pallet config.
@@ -339,9 +345,21 @@ impl ConfigDef {
 			false
 		};
 
+		let has_frame_system_supertrait = item.supertraits.iter().any(|s| {
+			syn::parse2::<ConfigBoundParse>(s.to_token_stream())
+				.map_or(false, |b| b.0 == *frame_system)
+		});
+
 		let mut has_event_type = false;
 		let mut consts_metadata = vec![];
-		let mut default_sub_trait = vec![];
+		let mut default_sub_trait = if enable_default {
+			Some(DefaultTrait {
+				items: Default::default(),
+				has_system: has_frame_system_supertrait,
+			})
+		} else {
+			None
+		};
 		for trait_item in &mut item.items {
 			let is_event = check_event_type(frame_system, trait_item, has_instance)?;
 			has_event_type = has_event_type || is_event;
@@ -382,13 +400,18 @@ impl ConfigDef {
 								"Duplicate #[pallet::no_default] attribute not allowed.",
 							))
 						}
+
 						already_no_default = true;
 					},
 				}
 			}
 
 			if !already_no_default && !is_event && enable_default {
-				default_sub_trait.push(trait_item.clone());
+				default_sub_trait
+					.as_mut()
+					.expect("is 'Some(_)' if 'enable_default'; qed")
+					.items
+					.push(trait_item.clone());
 			}
 		}
 
@@ -396,11 +419,6 @@ impl ConfigDef {
 			helper::take_first_item_pallet_attr(&mut item.attrs)?;
 		let disable_system_supertrait_check = attr.is_some();
 
-		let has_frame_system_supertrait = item.supertraits.iter().any(|s| {
-			syn::parse2::<ConfigBoundParse>(s.to_token_stream())
-				.map_or(false, |b| b.0 == *frame_system)
-		});
-
 		if !has_frame_system_supertrait && !disable_system_supertrait_check {
 			let found = if item.supertraits.is_empty() {
 				"none".to_string()