Not building on 1.47 anymore

[spacekookie]

For some reason this has stopped building.

error: `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, or `#[proc_macro_attribute]`
  --> /home/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-macro-0.3.7/src/lib.rs:31:1
   |
31 | pub fn join_internal(input: TokenStream) -> TokenStream {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, or `#[proc_macro_attribute]`
  --> /home/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-macro-0.3.7/src/lib.rs:37:1
   |
37 | pub fn try_join_internal(input: TokenStream) -> TokenStream {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, or `#[proc_macro_attribute]`
  --> /home/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-macro-0.3.7/src/lib.rs:43:1
   |
43 | pub fn select_internal(input: TokenStream) -> TokenStream {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, or `#[proc_macro_attribute]`
  --> /home/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-macro-0.3.7/src/lib.rs:49:1
   |
49 | pub fn select_biased_internal(input: TokenStream) -> TokenStream {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[taiki-e]

What platform and rust toolchain are you using? (os, target, rustc/cargo version, etc.)

Related: #2242

[Nemo157]

cargo tree -p futures-macro

may also be helpful, to see the proc-macro-hack etc. versions.

[taiki-e]

I think this is the same as either of the issues reported in #2242, so closing in favor of #2242. If you don't think so, we can reopen this.