[Enhancement] Throw an error when there are too many pallets

frame/support/procedural/src/construct_runtime/mod.rs

@@ -157,7 +157,7 @@ use proc_macro::TokenStream;
 use proc_macro2::TokenStream as TokenStream2;
 use quote::quote;
 use std::{collections::HashSet, str::FromStr};
-use syn::{Ident, Result};
+use syn::{spanned::Spanned, Ident, Result};
 
 /// The fixed name of the system pallet.
 const SYSTEM_PALLET_NAME: &str = "System";
@@ -184,6 +184,23 @@ fn construct_runtime_intermediary_expansion(
 	input: TokenStream2,
 	definition: ImplicitRuntimeDeclaration,
 ) -> Result<TokenStream2> {
+	let max_pallet_num = {
+		if cfg!(feature = "tuples-96") {
+			96
+		} else if cfg!(feature = "tuples-128") {
+			128
+		} else {
+			64
+		}
+	};
+
+	if definition.pallets.len() > max_pallet_num {
+		return Err(syn::Error::new(
+			input.span(),
+			"The number of pallets exceeds the maximum number of tuple elements.",
+		))
+	}
+
 	let frame_support = generate_crate_access_2018("frame-support")?;
 	let mut expansion = quote::quote!(
 		#frame_support::construct_runtime! { #input }

frame/support/test/tests/construct_runtime_ui/number_of_pallets_exceeds_tuple_size.rs

@@ -0,0 +1,77 @@
+use frame_support::construct_runtime;
+
+construct_runtime! {
+	pub struct Runtime where
+		UncheckedExtrinsic = UncheckedExtrinsic,
+		Block = Block,
+		NodeBlock = Block,
+	{
+		System: system::{},
+		Pallet1: pallet2::{},
+		Pallet3: pallet4::{},
+		Pallet5: pallet6::{},
+		Pallet7: pallet8::{},
+		Pallet9: pallet10::{},
+		Pallet11: pallet12::{},
+		Pallet13: pallet14::{},
+		Pallet15: pallet16::{},
+		Pallet17: pallet18::{},
+		Pallet19: pallet20::{},
+		Pallet21: pallet22::{},
+		Pallet23: pallet24::{},
+		Pallet25: pallet26::{},
+		Pallet27: pallet28::{},
+		Pallet29: pallet30::{},
+		Pallet31: pallet32::{},
+		Pallet33: pallet34::{},
+		Pallet35: pallet36::{},
+		Pallet37: pallet38::{},
+		Pallet39: pallet40::{},
+		Pallet41: pallet42::{},
+		Pallet43: pallet44::{},
+		Pallet45: pallet46::{},
+		Pallet47: pallet48::{},
+		Pallet49: pallet50::{},
+		Pallet51: pallet52::{},
+		Pallet53: pallet54::{},
+		Pallet55: pallet56::{},
+		Pallet57: pallet58::{},
+		Pallet59: pallet60::{},
+		Pallet61: pallet62::{},
+		Pallet63: pallet64::{},
+		Pallet65: pallet66::{},
+		Pallet67: pallet68::{},
+		Pallet69: pallet70::{},
+		Pallet71: pallet72::{},
+		Pallet73: pallet74::{},
+		Pallet75: pallet76::{},
+		Pallet77: pallet78::{},
+		Pallet79: pallet80::{},
+		Pallet81: pallet82::{},
+		Pallet83: pallet84::{},
+		Pallet85: pallet86::{},
+		Pallet87: pallet88::{},
+		Pallet89: pallet90::{},
+		Pallet91: pallet92::{},
+		Pallet93: pallet94::{},
+		Pallet95: pallet96::{},
+		Pallet97: pallet98::{},
+		Pallet99: pallet100::{},
+		Pallet101: pallet102::{},
+		Pallet103: pallet104::{},
+		Pallet105: pallet106::{},
+		Pallet107: pallet108::{},
+		Pallet109: pallet110::{},
+		Pallet111: pallet112::{},
+		Pallet113: pallet114::{},
+		Pallet115: pallet116::{},
+		Pallet117: pallet118::{},
+		Pallet119: pallet120::{},
+		Pallet121: pallet122::{},
+		Pallet123: pallet124::{},
+		Pallet125: pallet126::{},
+		Pallet127: pallet128::{},
+	}
+}
+
+fn main() {}

frame/support/test/tests/construct_runtime_ui/number_of_pallets_exceeds_tuple_size.stderr

@@ -0,0 +1 @@
+12344