Features incorrectly handled when dependency of bindep under both `dependencies` and `build-dependencies`

[benpye]

Problem

Cargo is incorrectly using the features from build-dependencies rather than dependencies when building the crate, in this case it causes a failure as the build target is no_std.

benpye@Bens-MacBook-Pro bindep_repro % cargo build --manifest-path parent/Cargo.toml --target riscv32im-unknown-none-elf -Zbuild-std=core 
   Compiling compiler_builtins v0.1.101
   Compiling core v0.0.0 (/Users/benpye/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core)
   Compiling parent v0.1.0 (/Users/benpye/git/bindep_repro/parent)
   Compiling rustc-std-workspace-core v1.99.0 (/Users/benpye/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling common_dep v0.1.0 (/Users/benpye/git/bindep_repro/common_dep)
error[E0463]: can't find crate for `std`
  |
  = note: the `riscv32im-unknown-none-elf` target may not support the standard library
  = note: `std` is required by `common_dep` because it does not declare `#![no_std]`
  = help: consider building the standard library from source with `cargo build -Zbuild-std`

For more information about this error, try `rustc --explain E0463`.
error: could not compile `common_dep` (lib) due to previous error
warning: build failed, waiting for other jobs to finish...

Steps

A minimal repro is available at https://github.com/benpye/rust_bugs/tree/bindep_feature_resolution_bug

The issue can be reproduced with

cargo build --manifest-path parent/Cargo.toml --target riscv32im-unknown-none-elf -Zbuild-std=core

The repro is made up of three crates.

• A has an artifact dependency on B with target = "target", and includes an (empty) build.rs script.
• B has both a regular dependency and build dependency on C, the build dependency enables the std feature on C.
• C is no_std when the std feature is not-enabled.

Possible Solution(s)

No response

Notes

• This also occurs when the crates are part of a workspace.
• This seems similar to bindep std errors when no_std bindep has a dependency which uses std in a build.rs #11772 but I needed an additional crate to trigger it.

Version

cargo 1.75.0-nightly (8eb8acbb1 2023-10-17)
release: 1.75.0-nightly
commit-hash: 8eb8acbb116e7923ea2ce33a50109933ed5ab375
commit-date: 2023-10-17
host: aarch64-apple-darwin
libgit2: 1.7.1 (sys:0.18.1 vendored)
libcurl: 8.1.2 (sys:0.4.68+curl-8.4.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1u  30 May 2023
os: Mac OS 14.0.0 [64-bit]

[weihanglo]

Looks like B (child in the repro) was built as an artifact dependency with target specified, so the entire dependency tree down from B was assumed to be built to target, and features are unified.

I am seeing this problem like,

• C (common_dep in the repro) as a normal dependency of B should
  • compile to target specified in --target
  • without feature std
• C as a build dependency of B should
  • compile to target specified in --target
  • but with feature std enabled

so that it will not be involved in "missing std" error. Is that correct?

[benpye]

That seems correct to me. The target should be respected but features still should not be unified between build dependencies and other dependencies under B. It should behave as though you did cargo build -p B --target=xyz.

[Lencerf]

I guess the issue is resolved by PR #15788

Reproduce the issue with cargo 1.93.0-nightly (5c0343317 2025-11-18)

➜ cargo version
cargo 1.93.0-nightly (5c0343317 2025-11-18)

➜ cargo build --manifest-path parent/Cargo.toml --target riscv32im-unknown-none-elf -Zbuild-std=core
   Compiling compiler_builtins v0.1.160 (/home/lencerf/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)
   Compiling core v0.0.0 (/home/lencerf/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling parent v0.1.0 (/home/lencerf/repo/rust_bugs/parent)
   Compiling common_dep v0.1.0 (/home/lencerf/repo/rust_bugs/common_dep)
error[E0463]: can't find crate for `std`
  |
  = note: the `riscv32im-unknown-none-elf` target may not support the standard library
  = note: `std` is required by `common_dep` because it does not declare `#![no_std]`
  = help: consider building the standard library from source with `cargo build -Zbuild-std`

error: cannot resolve a prelude import

For more information about this error, try `rustc --explain E0463`.
error: could not compile `common_dep` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...

With PR #15788 0360309,

➜ ~/repo/cargo/target/debug/cargo --version
cargo 1.93.0 (03603099f 2025-11-19)

➜ ~/repo/cargo/target/debug/cargo build --manifest-path parent/Cargo.toml --target riscv32im-unknown-none-elf -Zbuild-std=core
   Compiling compiler_builtins v0.1.160 (/home/lencerf/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)
   Compiling core v0.0.0 (/home/lencerf/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling parent v0.1.0 (/home/lencerf/repo/rust_bugs/parent)
   Compiling common_dep v0.1.0 (/home/lencerf/repo/rust_bugs/common_dep)
   Compiling child v0.1.0 (/home/lencerf/repo/rust_bugs/child)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.35s

build succeeded.

[weihanglo]

Yeah, resolved via #15788. Thanks!