Compact trait bounds overflow

[ascjones]

When integrating the latest scale-info master into substrate (see https://github.com/paritytech/substrate/compare/aj-metadata-vnext) I receive the following error:

It appears to have been introduced in #53.

Removing the TypeInfo derive on MultiAddress makes it compile:

diff --git a/primitives/runtime/src/multiaddress.rs b/primitives/runtime/src/multiaddress.rs
index a47201008..d09cd7aca 100644
--- a/primitives/runtime/src/multiaddress.rs
+++ b/primitives/runtime/src/multiaddress.rs
@@ -21,7 +21,7 @@ use codec::{Encode, Decode};
 use sp_std::vec::Vec;
 
 /// A multi-format address wrapper for on-chain accounts.
-#[derive(Encode, Decode, PartialEq, Eq, Clone, crate::RuntimeDebug, scale_info::TypeInfo)]
+#[derive(Encode, Decode, PartialEq, Eq, Clone, crate::RuntimeDebug)]
 #[cfg_attr(feature = "std", derive(Hash))]
 pub enum MultiAddress<AccountId, AccountIndex> {
 	/// It's an account ID (pubkey).
diff --git a/primitives/runtime/src/traits.rs b/primitives/runtime/src/traits.rs
index 00fae6fe6..0fdf6d55b 100644
--- a/primitives/runtime/src/traits.rs
+++ b/primitives/runtime/src/traits.rs
@@ -203,7 +203,7 @@ pub trait Lookup {
 /// context.
 pub trait StaticLookup {
 	/// Type to lookup from.
-	type Source: Codec + Clone + PartialEq + Debug + scale_info::TypeInfo;
+	type Source: Codec + Clone + PartialEq + Debug;
 	/// Type to lookup into.
 	type Target;
 	/// Attempt a lookup.

Here is the expanded derived TypeInfo impl for MultiAddress:

impl<AccountId, AccountIndex> ::scale_info::TypeInfo for MultiAddress<AccountId, AccountIndex>
        where
            AccountId: ::scale_info::TypeInfo + 'static,
            AccountIndex: ::codec::HasCompact,
            <AccountIndex as ::codec::HasCompact>::Type: ::scale_info::TypeInfo + 'static,
            AccountId: ::scale_info::TypeInfo + 'static,
            AccountIndex: ::scale_info::TypeInfo + 'static,
        {
            type Identity = Self;
            fn type_info() -> ::scale_info::Type {
                ::scale_info::Type::builder()
                    .path(::scale_info::Path::new(
                        "MultiAddress",
                        "sp_runtime::multiaddress",
                    ))
                    .type_params(<[_]>::into_vec(box [
                        ::scale_info::meta_type::<AccountId>(),
                        ::scale_info::meta_type::<AccountIndex>(),
                    ]))
                    .variant(
                        ::scale_info::build::Variants::with_fields()
                            .variant(
                                "Id",
                                ::scale_info::build::Fields::unnamed()
                                    .field_of::<AccountId>("AccountId"),
                            )
                            .variant(
                                "Index",
                                ::scale_info::build::Fields::unnamed()
                                    .compact_of::<AccountIndex>("AccountIndex"),
                            )
                            .variant(
                                "Raw",
                                ::scale_info::build::Fields::unnamed()
                                    .field_of::<Vec<u8>>("Vec<u8>"),
                            )
                            .variant(
                                "Address32",
                                ::scale_info::build::Fields::unnamed()
                                    .field_of::<[u8; 32]>("[u8; 32]"),
                            )
                            .variant(
                                "Address20",
                                ::scale_info::build::Fields::unnamed()
                                    .field_of::<[u8; 20]>("[u8; 20]"),
                            ),
                    )
            }
        };

[ascjones]

Managed to repro in scale-info finally, could do with some more minimization but here is what I have so far:

    #[allow(unused)]
    #[derive(Encode, scale::Decode, TypeInfo)]
    enum MutilatedMultiAddress<AccountId, AccountIndex> {
        Id(AccountId),
        Index(#[codec(compact)] AccountIndex),
        Address32([u8; 32]),
    }

    pub trait StaticLookup {
        type Source: scale::Codec // works
        /// Type to lookup from.
        // type Source: scale::Codec + TypeInfo + 'static; // recursion error
    }

    pub struct AccountIdLookup<AccountId, AccountIndex>(PhantomData<(AccountId, AccountIndex)>);

    impl<AccountId, AccountIndex> StaticLookup for AccountIdLookup<AccountId, AccountIndex>
        where
            AccountId: scale::Codec + Clone + PartialEq + scale_info::TypeInfo + 'static,
            AccountIndex: scale::Codec + Clone + PartialEq + scale_info::TypeInfo + 'static,
            MutilatedMultiAddress<AccountId, AccountIndex>: scale::Codec,
    {
        type Source = MutilatedMultiAddress<AccountId, AccountIndex>;
    }

[dvdplm]

Managed to repro in scale-info finally,

Confirmed, I see it here too.

[ascjones]

The fix for this particaular snippet is to remove the TypeInfo + 'static bounds for the StaticLookup from AccountId and AccountIndex and add them instead to MutilatedMultiAddress<AccountId, AccountIndex>.

Edit: I think just adding to MutilatedMultiAddress<AccountId, AccountIndex> is enough, see #66.

    pub trait StaticLookup {
        type Source: scale::Codec + TypeInfo + 'static;
    }

    struct AccountIdLookup<AccountId, AccountIndex>(PhantomData<(AccountId, AccountIndex)>);

    impl<AccountId, AccountIndex> StaticLookup for AccountIdLookup<AccountId, AccountIndex>
        where
            AccountId: scale::Codec + Clone + PartialEq,
            AccountIndex: scale::Codec + Clone + PartialEq,
            MutilatedMultiAddress<AccountId, AccountIndex>: scale::Codec + TypeInfo + 'static,
    {
        type Source = MutilatedMultiAddress<AccountId, AccountIndex>;
    }

[ascjones]

Note the fix for the above snippet is to apply the TypeInfo bounds to the MultiAddress rather than the type parameters themselves:

    AccountId: Codec + Clone + PartialEq + Debug,
    AccountIndex: Codec + Clone + PartialEq + Debug,
    crate::MultiAddress<AccountId, AccountIndex>: Codec + scale_info::TypeInfo + 'static,

Also see rust-lang/rust#81785 for the rust issue to improve the error message.