1496144 - Building mobile/android fails to build goblin with Rust stable: "#![feature] may not be used on the stable release channel"

Status: RESOLVED FIXED

(Firefox Build System :: General, defect)

Description

[Nick Alexander :nalexander [he/him]]

I had multiple reports in #gv on (private) Mozilla slack complaining that building mobile/android (for GeckoView) was failing with:

   Compiling goblin v0.0.17
error[E0554]: #![feature] may not be used on the stable release channel
  --> third_party/rust/goblin/src/lib.rs:82:59
   |
82 | #![cfg_attr(all(feature = "alloc", not(feature = "std")), feature(alloc))]

These were fixed by `rustup default nightly`.  I don't have the exact version of Rust stable that folks were complaining about, but locally I have:

$ rustup run stable rustc --version                                                                                                                                                                                             rustc 1.28.0 (9634041f0 2018-07-30)
$ rustup run nightly rustc --version                                                                                                                                                                                             rustc 1.30.0-nightly (6e0f1cc15 2018-09-05)

That seems reasonable, since beta is 1.29.0.  Maybe we really require beta (not nightly) and that isn't well communicated?

:ted.mielczarek suggests that this is fallout from https://bugzilla.mozilla.org/show_bug.cgi?id=1457481, although I'll leave it to him to set the dependency fields.

Comment 1

[(not currently active) Ted Mielczarek]

As a short-term workaround, you should be able to use `ac_add_options --enable-rust-simd`.

The issue here is that bug 1457481 added a dependency on the Rust object/goblin crates for Android, and is using `default-features = false`:
https://hg.mozilla.org/mozilla-central/file/7566a6bac33d/tools/profiler/rust-helper/Cargo.toml#l8

I believe the right fix is to make that crate's `parse_elf` feature require the `std` feature in object here:
https://hg.mozilla.org/mozilla-central/file/7566a6bac33d/tools/profiler/rust-helper/Cargo.toml#l15

More detailed explanation:

object also uses `default-features = false` for goblin but enables most of its features:
https://hg.mozilla.org/mozilla-central/file/255e04ebe3bd/third_party/rust/object/Cargo.toml#l28

except `std` which is forwarded from object's `std` feature (which rust-helper disables, per above):
https://hg.mozilla.org/mozilla-central/file/255e04ebe3bd/third_party/rust/object/Cargo.toml#l48

...and if you disable the `std` and `alloc` features in goblin, it asks rustc for the `alloc` feature:
https://hg.mozilla.org/mozilla-central/file/255e04ebe3bd/third_party/rust/goblin/src/lib.rs#l81

`#![feature(...)` is not allowed on stable, so `#![feature(alloc)` breaks. (The `alloc` crate is not quite stable: https://github.com/rust-lang/rfcs/pull/2480 .)

This doesn't break in CI because all of our CI builds use `--enable-rust-simd`:
https://dxr.mozilla.org/mozilla-central/rev/17c314f6930d2b8d6e456aa9e9d41407a45c3008/build/mozconfig.rust#12

...and that intentionally uses `RUSTC_BOOTSTRAP=1` to unlock unstable Rust features:
https://dxr.mozilla.org/mozilla-central/rev/17c314f6930d2b8d6e456aa9e9d41407a45c3008/config/rules.mk#910

Comment 2

[James Willcox (:snorp) ([e-mail]) (he/him)]

How is this building on automation if we're using stable rust there?

Comment 3

[(not currently active) Ted Mielczarek]

Per comment 1, all of our CI builds use `--enable-rust-simd`.

Comment 4

[Markus Stange [:mstange]]

Thanks for the investigation, Ted! I'm taking a look at this now.

Comment 5

[Matt Brubeck (:mbrubeck)]

Attachment: Bug 1496144 - Enable std feature for object crate. r=mstange

Comment 6

[(not currently active) Ted Mielczarek]

I filed bug 1496199 on standing up an Android build that would have caught this, since we already have builds like that for desktop Firefox.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/275985ae0d13
Enable std feature for object crate. r=mstange

Comment 8

[Mike Hommey [:glandium]]

(In reply to Ted Mielczarek [:ted] [:ted.mielczarek] from comment #1)
> ...and that intentionally uses `RUSTC_BOOTSTRAP=1` to unlock unstable Rust
> features:
> https://dxr.mozilla.org/mozilla-central/rev/
> 17c314f6930d2b8d6e456aa9e9d41407a45c3008/config/rules.mk#910

And this is why RUSTC_BOOTSTRAP being set too broadly is hurting.

Comment 9

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/275985ae0d13