Regression with macros in types on serde_derive

[Manishearth]

serde_derive 0.0.94 compiles just fine with 2019-06-06's nightly, but is broken with 2019-06-11:

error[E0433]: failed to resolve: unresolved import
   --> src/internals/ast.rs:142:44
    |
142 |     variants: &'a Punctuated<syn::Variant, Token![,]>,
    |                                            ^^^^^^^^^
    |                                            |
    |                                            unresolved import
    |                                            help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

[09:23:31] मanishearth@noether ~/sand/serde_derive ^_^ 
$ cargo +nightly-2019-07-11 build
   Compiling proc-macro2 v0.4.30
   Compiling unicode-xid v0.1.0
   Compiling syn v0.15.39
   Compiling quote v0.6.12
   Compiling serde_derive v1.0.94 (/home/manishearth/sand/serde_derive)
error[E0433]: failed to resolve: unresolved import
   --> src/internals/ast.rs:142:44
    |
142 |     variants: &'a Punctuated<syn::Variant, Token![,]>,
    |                                            ^^^^^^^^^
    |                                            |
    |                                            unresolved import
    |                                            help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
   --> src/internals/ast.rs:187:40
    |
187 |     fields: &'a Punctuated<syn::Field, Token![,]>,
    |                                        ^^^^^^^^^
    |                                        |
    |                                        unresolved import
    |                                        help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
    --> src/internals/attr.rs:1542:44
     |
1542 |     metas: &'a Punctuated<syn::NestedMeta, Token![,]>,
     |                                            ^^^^^^^^^
     |                                            |
     |                                            unresolved import
     |                                            help: a similar path exists: `syn::token`
     |
     = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
    --> src/internals/attr.rs:1586:44
     |
1586 |     items: &'a Punctuated<syn::NestedMeta, Token![,]>,
     |                                            ^^^^^^^^^
     |                                            |
     |                                            unresolved import
     |                                            help: a similar path exists: `syn::token`
     |
     = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
    --> src/internals/attr.rs:1594:44
     |
1594 |     items: &'a Punctuated<syn::NestedMeta, Token![,]>,
     |                                            ^^^^^^^^^
     |                                            |
     |                                            unresolved import
     |                                            help: a similar path exists: `syn::token`
     |
     = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
    --> src/internals/attr.rs:1602:41
     |
1602 |     items: &Punctuated<syn::NestedMeta, Token![,]>,
     |                                         ^^^^^^^^^
     |                                         |
     |                                         unresolved import
     |                                         help: a similar path exists: `syn::token`
     |
     = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
    --> src/internals/attr.rs:1702:56
     |
1702 |     struct BorrowedLifetimes(Punctuated<syn::Lifetime, Token![+]>);
     |                                                        ^^^^^^^^^
     |                                                        |
     |                                                        unresolved import
     |                                                        help: a similar path exists: `syn::token`
     |
     = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
   --> src/bound.rs:198:31
    |
198 |                 colon_token: <Token![:]>::default(),
    |                               ^^^^^^^^^
    |                               |
    |                               unresolved import
    |                               help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
   --> src/bound.rs:232:27
    |
232 |             colon_token: <Token![:]>::default(),
    |                           ^^^^^^^^^
    |                           |
    |                           unresolved import
    |                           help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
   --> src/bound.rs:289:36
    |
289 |                         lt_token: <Token![<]>::default(),
    |                                    ^^^^^^^^^
    |                                    |
    |                                    unresolved import
    |                                    help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
   --> src/bound.rs:309:36
    |
309 |                         gt_token: <Token![>]>::default(),
    |                                    ^^^^^^^^^
    |                                    |
    |                                    unresolved import
    |                                    help: a similar path exists: `syn::token`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0433]: failed to resolve: unresolved import
  --> src/fragment.rs:58:18
   |
58 |                 <Token![,]>::default().to_tokens(out);
   |                  ^^^^^^^^^
   |                  |
   |                  unresolved import
   |                  help: a similar path exists: `syn::token`
   |
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error: aborting due to 12 previous errors

For more information about this error, try `rustc --explain E0433`.
error: Could not compile `serde_derive`.

Something weird is going on with that macro.

cc @dtolnay @eddyb

[matthiaskrgr]

Looks like #62562 ?

[Manishearth]

#62562