defmt-0.3.9 failed to build

[jonathanpallant]

Crate name

defmt

Build failure link

https://docs.rs/crate/defmt/0.3.9/builds/1566395

Additional details

I don't think we changed anything substantial since defmt-0.3.8, which built OK.

[syphar]

there wasn't any related change in docs.rs, though I can only imagine it's either related to your code, or perhaps that the new nightly version changed something.

[GuillaumeGomez]

Maybe -Zbuild-std is the one in fault here?

[syphar]

this is the diff: knurling-rs/defmt@defmt-v0.3.8...defmt-v0.3.9

[syphar]

ah, I remember there is also diff.rs: https://diff.rs/defmt/0.3.8/defmt/0.3.9/Cargo.toml

[jonathanpallant]

Do you use -Zbuild-std? Because I don't think we do. And yes, on thumbv6m-none-eabi for example, I'm pretty sure you have to say -Zbuild-std=core

➜  defmt git:(release-defmt-0.3.10) rustc +nightly --version
rustc 1.83.0-nightly (06bb8364a 2024-10-01)
➜  defmt git:(release-defmt-0.3.10) cargo +nightly build --target=thumbv6m-none-eabi
   Compiling bitflags v1.3.2
   Compiling defmt v0.3.9 (/Users/jonathan/Documents/knurling-rs/defmt/defmt)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
➜  defmt git:(release-defmt-0.3.10) cargo +nightly build --target=thumbv6m-none-eabi -Zbuild-std
   Compiling gimli v0.29.0
error[E0432]: unresolved import `alloc::sync`
 --> /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gimli-0.29.0/src/read/dwarf.rs:2:12
  |
2 | use alloc::sync::Arc;
  |            ^^^^ could not find `sync` in `alloc`

error[E0432]: unresolved import `alloc::sync`
 --> /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gimli-0.29.0/src/read/abbrev.rs:4:12
  |
4 | use alloc::sync::Arc;
  |            ^^^^ could not find `sync` in `alloc`

For more information about this error, try `rustc --explain E0432`.
error: could not compile `gimli` (lib) due to 2 previous errors
➜  defmt git:(release-defmt-0.3.10) cargo +nightly build --target=thumbv6m-none-eabi -Zbuild-std=core
   Compiling bitflags v1.3.2
   Compiling defmt v0.3.9 (/Users/jonathan/Documents/knurling-rs/defmt/defmt)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.25s
➜  defmt git:(release-defmt-0.3.10)

[jonathanpallant]

The error message appears to come from here: https://github.com/rust-lang/cargo/blob/81e0670dddefc0b78b272e58decc0eea9def3720/src/cargo/core/compiler/standard_lib.rs#L80

[jonathanpallant]

Which was added last week: rust-lang/cargo@5e4a1db

[jonathanpallant]

Yup:

➜  defmt git:(release-defmt-0.3.10) RUSTC=~/Downloads/rust-nightly/rust-nightly-aarch64-apple-darwin/rustc/bin/rustc  ~/Downloads/rust-nightly/rust-nightly-aarch64-apple-darwin/cargo/bin/cargo build --target=thumbv6m-none-eabi -Zbuild-std
error: building std is not supported on the following targets: thumbv6m-none-eabi

➜  defmt git:(release-defmt-0.3.10) RUSTC=~/Downloads/rust-nightly/rust-nightly-aarch64-apple-darwin/rustc/bin/rustc  ~/Downloads/rust-nightly/rust-nightly-aarch64-apple-darwin/cargo/bin/cargo build --target=thumbv6m-none-eabi -Zbuild-std=core
error: "/Users/jonathan/Downloads/rust-nightly/rust-nightly-aarch64-apple-darwin/rustc/lib/rustlib/src/rust/library/Cargo.lock" does not exist, unable to build with the standard library, try:
        rustup component add rust-src

No idea how to add rust-src to a tarball installation, but that's the error.

[jonathanpallant]

I sent https://crates.io/crates/thejpster-test-docs-target down the line, which is an inoffensive test crate. If you can't build it then I'm pretty sure it's a docs.rs but and not a defmt bug.

[syphar]

Maybe -Zbuild-std is the one in fault here?

@GuillaumeGomez you mean we need add it do the docs.rs metadata to use #2107 ?

I sent https://crates.io/crates/thejpster-test-docs-target down the line, which is an inoffensive test crate. If you can't build it then I'm pretty sure it's a docs.rs but and not a defmt bug.

there was no docs.rs change that might cause this, so I imagine the nighty version changes you linked could cause the error.

If you have a test crate that errors too (and IMO it likely will with the targets) we might try it with cargo-args=["-Zbuild-std"]

[GuillaumeGomez]

It's not clear when it's needed. Also, I'm surprised it worked without using -Zbuild-std (I thought we used it but we don't).

[jonathanpallant]

AFAIK will need -Zbuild-std=core when building for a target that doesn't have libstd. I guess most of your crates build for the host machine, but the docs.rs metadata for this one forces you to build it for thumbv6m-none-eabi and thumbv7em-none-eabihf, because it's known to not work on Windows/macOS/Linux.

[jonathanpallant]

https://crates.io/crates/thejpster-test-docs-target is perpetually stuck at the back of the queue, perhaps because you've rated as a crate of low value (it is, it's terrible).

[syphar]

https://crates.io/crates/thejpster-test-docs-target is perpetually stuck at the back of the queue, perhaps because you've rated as a crate of low value (it is, it's terrible).

it's not deprioritized, so has the same prio as normal releases (deprioritized is shown in braces after the crate, if we do it, like (priority: -1))