derive_impl doesn't seems to handle path correctly. Errors rise when using reexport

[gui1117]

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• This is not a support question.

Description of bug

When changing the path a little when invoking the derive_impl macro error arises.

derive_impl seems to require some item to be accessible from the first ident of the path of its first argument.

Steps to reproduce

1- change the frame-default-config-example a little by basically using a path with something in front of frame_system

diff --git a/frame/examples/default-config/src/lib.rs b/frame/examples/default-config/src/lib.rs
index adb2469e92f..4f236040796 100644
--- a/frame/examples/default-config/src/lib.rs
+++ b/frame/examples/default-config/src/lib.rs
@@ -130,7 +130,10 @@ pub mod tests {
                }
        );
 
-       #[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+       pub mod bar {
+               pub use frame_system;
+       }
+       #[derive_impl(bar::frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
        impl frame_system::Config for Test {
                // these items are defined by frame-system as `no_default`, so we must specify them here.
                // Note that these are types that actually rely on the outer runtime, and can't sensibly

2- see the error:

error[E0433]: failed to resolve: could not find `__export_tokens_tt_test_default_config` in `bar`
   --> frame/examples/default-config/src/lib.rs:136:2
    |
136 |     #[derive_impl(bar::frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ could not find `__export_tokens_tt_test_default_config` in `bar`
    |
    = note: this error originates in the macro `frame_support::macro_magic::forward_tokens` (in Nightly builds, run with -Z macro-backtrace for more info)

[bkchr]

CC @sam0x17

[sam0x17]

We (thanks to @thiolliere!) are working on a fix to macro_magic that will address this and a few other things. Thanks again !!!! 👍🏻

See here:

• Revamp / v0.4 sam0x17/macro_magic#3
• Remove need for use_attr and use_proc sam0x17/macro_magic#5
• Avoid discarding error when failing to parse a path sam0x17/macro_magic#4