Has anyone ever encountered this error while trying to compile pants itself?

error[E0658]: use of unstable library feature `result_flattening`
...
error: could not compile `sharded_lmdb` (lib) due to 7 previous errors
warning: build failed, waiting for other jobs to finish...

This is on

main

?

yup. full build error:

 pants fmt
[=== 00:00 Building native code... ===]
  Downloaded pyo3-build-config v0.27.2
  Downloaded pyo3-macros-backend v0.27.2
  Downloaded pyo3-macros v0.27.2
  Downloaded pyo3-ffi v0.27.2
  Downloaded pyo3 v0.27.2
  Downloaded 5 crates (1.3MiB) in 3.71s (largest was `pyo3` at 1.1MiB)
   Compiling pyo3-build-config v0.27.2
   Compiling sharded_lmdb v0.0.1 (/Users/alex/Projects/pants/src/rust/sharded_lmdb)
   Compiling logging v0.0.1 (/Users/alex/Projects/pants/src/rust/logging)
   Compiling generic-array v0.14.7
   Compiling nails v0.13.0
   Compiling tree-sitter-typescript v0.23.2
   Compiling tree-sitter-dockerfile v0.3.0 (<https://github.com/pantsbuild/tree-sitter-dockerfile.git?rev=508588913c93a30e7ef09a4ac3ecdee955b7b950#50858891>)
   Compiling tree-sitter-python v0.25.0
error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:300:14
    |
300 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:370:14
    |
370 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:430:14
    |
430 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:517:14
    |
517 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:613:14
    |
613 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

   Compiling uname v0.1.1
error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:636:14
    |
636 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

error[E0658]: use of unstable library feature `result_flattening`
   --> sharded_lmdb/src/lib.rs:689:14
    |
689 |             .flatten()
    |              ^^^^^^^
    |
    = note: see issue #70142 <<https://github.com/rust-lang/rust/issues/70142>> for more information

   Compiling rayon-core v1.12.1
   Compiling peg-runtime v0.8.5
   Compiling tree-sitter-language v0.1.5
   Compiling parking v2.2.1
   Compiling serde_spanned v0.6.9
For more information about this error, try `rustc --explain E0658`.
error: could not compile `sharded_lmdb` (lib) due to 7 previous errors
warning: build failed, waiting for other jobs to finish...

Hmm, it's not happening in CI as far as I can tell, so that's bizarre. Assuming rustup is installed, it should grab the toolchain file, and then be good to go. What OS/platform are you running on? I'm about to dash out of the office, unfortunately, so I can't help right now. But I can look into it when I'm back tonight

That would be great! I have rustup installed. was using stable, tried switching to nightly when i ran into this, didn't change anything. I'm on macos-aarch64

We use 1.91 right now, with a PR for 1.92 in progress

just to confirm:

cd src/rust
cargo build --features=extension-module --release -p engine -p client -p sandboxer

as specified in

{ROOT}/pants

shell sources, produces the same errors

Very weird.

result_flattening

was stabilized in Rust 1.74.0 and we are well past that

ok, that's extra weird! the contents of

src/rust/rust-toolchain

match what's on github:

[toolchain]
channel = "1.91.0"
# NB: We don't list the components (namely `clippy` and `rustfmt`) and instead rely on either the
#  the profile being "default" (by-and-large the default profile) or the nice error message from
#  `cargo fmt` and `cargo clippy` if the required component isn't installed
#  This is so the Pants-compiled engine (which uses the "minimal" profile) doesn't download/install
#  these as they are unnecessary.

my rustup stable toolchain version is 1.91.1 and my rustup nightly toolchain is 1.93.0

So something is wrong with our bootstrapping logic, since I'm pretty sure the toolchain should be controlled by the toolchain file above

yup, rustup is installed and should be working, but the rustc/cargo provided by homebrew overrides the rustc/cargo provided by rustup, and ignored the

rust-toolchain

file. uninstalling homebrew's rust allowedrustup's rust to kick in and it worked immediately. pants was able to successfully compile. maybe there's a way for the bootstrapping logic to detect if it's running cargo/rustc provided by rustup and warn if it isn't... I'm not really sure.

Great!

Funnily enough, something similar to this is why I deleted all my rust/cargo - I didn't see anything like this, but Homebrew doing weird stuff overall.