Cannot fing type AtomicU128 error

[nical]

Hi,

In Firefox's build system we are running into this error:

 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u8
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u8
 INFO -  [crossbeam-epoch 0.8.0] cargo:rustc-cfg=has_min_const_fn
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u16
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u16
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u32
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u32
 INFO -       Running `/builds/worker/workspace/obj-build/release/build/crossbeam-utils-aca7e78e5e03b092/build-script-build`
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u64
 INFO -  [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u64
ERROR -  [crossbeam-utils 0.8.1] error[E0412]: cannot find type `AtomicU128` in module `core::sync::atomic`
 INFO -  [crossbeam-utils 0.8.1]     --> <anon>:1:38
 INFO -  [crossbeam-utils 0.8.1]      |
 INFO -  [crossbeam-utils 0.8.1] 1    |   pub type Probe = core::sync::atomic::AtomicU128;
 INFO -  [crossbeam-utils 0.8.1]      |                                        ^^^^^^^^^^ help: a struct with a similar name exists: `AtomicU16`
 INFO -  [crossbeam-utils 0.8.1]      |
 INFO -  [crossbeam-utils 0.8.1]     ::: /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2139:1
 INFO -  [crossbeam-utils 0.8.1]      |
 INFO -  [crossbeam-utils 0.8.1] 2139 | / atomic_int! {
 INFO -  [crossbeam-utils 0.8.1] 2140 | |     cfg(target_has_atomic = "16"),
 INFO -  [crossbeam-utils 0.8.1] 2141 | |     cfg(target_has_atomic_equal_alignment = "16"),
 INFO -  [crossbeam-utils 0.8.1] 2142 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
 INFO -  [crossbeam-utils 0.8.1] ...    |
 INFO -  [crossbeam-utils 0.8.1] 2155 | |     u16 AtomicU16 ATOMIC_U16_INIT
 INFO -  [crossbeam-utils 0.8.1] 2156 | | }
 INFO -  [crossbeam-utils 0.8.1]      | |_- similarly named struct `AtomicU16` defined here
 INFO -  [crossbeam-utils 0.8.1]
ERROR -  [crossbeam-utils 0.8.1] error: aborting due to previous error
 INFO -  [crossbeam-utils 0.8.1]
 INFO -  [crossbeam-utils 0.8.1] For more information about this error, try `rustc --explain E0412`.

I am seeing it on a linux64 build, it might happen on other platforms as well.
It doesn't actually prevent the build from completing, but it confuses Firefox's build system and CI.

I'm not quite sure why this is happening. Is there a feature flag or something that could help with avoiding this error message, or something to adjust in crossbeam-utils?

[taiki-e]

This is the output when probe*/emit* methods of autocfg check if the code can be compiled. It has no effect on the build.

crossbeam/crossbeam-utils/build.rs

Line 22 in 99c66ec

cfg.emit_type_cfg("core::sync::atomic::AtomicU128", "has_atomic_u128");

But I'm not sure why this is displayed to the user... I thought the content of the error on probe*/emit* would never be displayed.

cc @cuviper

[taiki-e]

INFO - [crossbeam-utils 0.8.1] cargo:rustc-cfg=has_atomic_u8

Hmm, does firefox's build system seem to get and parse the output of build scripts?
Then, if the output contains a string like "error", does firefox's build system seem to assume it as "an error has occurred"?

If the above assumptions are correct, this is a false positive of firefox's build system seem and probably could be fixed on firefox or autocfg side, but nothing on the crossbeam side.

[nical]

I'm trying to figure out what our tooling is doing, but I don't think that we can easily work around it. The way we parse errors is more involved than matching for "error", of course, but this one looks like it is produced by rustc so it is hard to distinguish it from normal build breaking errors by looking at the formatting.

I hadn't realized that this is coming from autofcg which is outside of crossbeam.

[nical]

Moved this to cuviper/autocfg#30.