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Bad error message when using attributes proc_macro #52469
Description
Upgrading Servo to today’s Nightly caused a confusing pair of error messages:
error[E0432]: unresolved import `dom_struct::dom_struct`
--> components/script/dom/htmlulistelement.rs:10:5
|
10 | use dom_struct::dom_struct;
| ^^^^^^^^^^^^^^^^^^^^^^ no `dom_struct` in the root
error[E0658]: The attribute `dom_struct` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
--> components/script/dom/bluetoothpermissionresult.rs:26:1
|
26 | #[dom_struct]
| ^^^^^^^^^^^^^
|
= help: add #![feature(custom_attribute)] to the crate attributes to enableAdding #[macro_use] changes the second error to:
error[E0658]: attribute procedural macros are experimental (see issue #38356)
--> components/script/dom/attr.rs:28:1
|
28 | #[dom_struct]
| ^^^^^^^^^^^^^
|
::: components/script/lib.rs:35:1
|
35 | #[macro_use] extern crate dom_struct;
| ------------ procedural macro imported here
|
= help: add #![feature(proc_macro)] to the crate attributes to enableAll three messages are wrong:
dom_struct::dom_structdoes existfeature(custom_attribute)is not the correct fixfeature(proc_macro)is not only not the correct fix, it was already present!
The correct fix is to add #![feature(use_extern_macros)], but the only way to figure that out is to read #52081.
Activity
alexcrichton commentedon Jul 17, 2018
I believe this is largely fixed with #52458, and the remaining pieces will be fixed by #50911
arcriley commentedon Jul 18, 2018
Is there a way to roll back to a previous nightly?
SimonSapin commentedon Jul 18, 2018
@arcriley You can run
rustup install nightly-2018-07-15andcargo +nightly-2018-07-15 build, for example. Or use a directory override or a toolchain file: https://github.com/rust-lang-nursery/rustup.rs/#toolchain-specificationdominikwerder commentedon Jul 18, 2018
Thank you @SimonSapin
steveklabnik commentedon Sep 17, 2019
Both PRs that were said to fix this have been closed; given that this issue is over a year old, and that it's going to be hard to reproduce, I'm going to give this a close. @SimonSapin if you have a way to reproduce this today, let me know and we can re-open!
SimonSapin commentedon Sep 17, 2019
I suspect that other things have been stabilized in the meantime and this is no longer relevant.