Misleading error messages when using the wrong macro fragment specifiers

Issue:

#[rustfmt::skip]
mod issue {
    struct SomeType<T>(std::marker::PhantomData<T>);

    macro_rules! test {
        ($ty:ty) => {
            impl<$ty,> SomeType<$ty> {}
        };
    }

    // Works fine
    impl<T,> SomeType<T> {}
    //   error: expected one of `>` or `as`, found `,`
    //   --> src\lib.rs:7:21
    //    |
    // 7  |             impl<$ty,> SomeType<$ty> {}
    //    |                     ^ expected one of `>` or `as`
    // ...
    // 12 |     test!(T);
    //    |     -------- in this macro invocation
    test!(T);

    macro_rules! test2 {
        ($ty:ty) => {
            impl<$ty> SomeType<$ty> {}
        };
    }

    // Works fine
    impl<T> SomeType<T> {}
    // error: expected `::`, found `SomeType`
    //   --> src\lib.rs:17:23
    //    |
    // 17 |             impl<$ty> SomeType<$ty> {}
    //    |                       ^^^^^^^^ expected `::`
    // ...
    // 22 |     test2!(T);
    //    |     --------- in this macro invocation
    test2!(T);
}

The macro should behave exactly like its manual expansion would; I've inlined the reported problems into the code.

Meta

The error happens in both stable and nightly toolchains, on linux and windows

rustc --version --verbose:

rustc 1.82.0 (f6e511eec 2024-10-15)
binary: rustc
commit-hash: f6e511eec7342f59a25f7c0534f1dbea00d01b14
commit-date: 2024-10-15
host: x86_64-pc-windows-msvc
release: 1.82.0
LLVM version: 19.1.1

Start by running the inline macro reproducer with the affected rustc toolchain and compare its diagnostics with the manual expansions shown in the issue. The issue names no source files or tests, so locate the compiler handling for macro fragment expansion and diagnostics. Done means the macro errors communicate the corresponding manual-expansion problem rather than pointing to misleading tokens.