[tamaro-skaljic]

Note: This pull request's description and code changes were generated using AI, but reviewed by me.

This PR contains only the fix, but an end-to-end test exists on a separate branch, see below.
If the test should be added to the repository, let me know and I will add the commits here too.

The Issue

Fixes #343.

Cargo's new warn-by-default lint cargo::unused_workspace_dependencies, in beta 1.100 and nightly, warns about every [workspace.dependencies] entry that no workspace member inherits.

trybuild copies the whole table into the generated manifest, but the generated package inherits only the entries that the crate under test uses. So every Cargo invocation by trybuild warns once for each of the other entries. The warnings appear while the dependencies build, and again in the STDERR block of every pass test.

The Solution

With this PR trybuild copies only the entries that the generated package inherits with workspace = true, from its [dependencies], which include the dev-dependencies, or from any [target.*.dependencies].

Dropping the other entries can't change resolution, because Cargo only uses a workspace dependency through a member that inherits it.

Considered Alternatives

Allowing the lint instead doesn't work:

• [lints.cargo] in the generated package doesn't affect this workspace-level lint.

• [workspace.lints.cargo] silences it, but Cargo without stable cargo lints, such as 1.98.1 and 1.93.0, then warns unused manifest key `lints.cargo` on every invocation.

Verification / Testing

See tests/test_workspace.rs, on branch test/issue-343-unused-workspace-dependency-warnings.

The test writes a fixture workspace into CARGO_TARGET_TMPDIR. There, the crate under test inherits workspace dependencies through [dependencies], [dev-dependencies] (with trybuild itself), [build-dependencies], [target.'cfg(unix)'.dependencies] and [target.'cfg(windows)'.dev-dependencies]. A second member inherits the crate under test and an entry of its own.

The test runs cargo test there, over a pass + compile_fail suite and a compile_fail-only suite, and asserts three things:

• the run succeeds;

• nothing prints unused workspace dependency;

• the generated [workspace.dependencies] holds exactly the four inherited entries.

Building the fixture compiles trybuild a second time, which took about 16 seconds on a cold cache here and 7 seconds warm.

On Windows, it also needs a checkout path shorter than about 118 characters, because link.exe can't write the deeper paths of the fixture's binaries.

Results on Windows 11, with RUSTFLAGS=-Dwarnings:

Toolchain	Before the fix	After the fix
nightly: cargo 1.100.0-nightly (7941be6fb 2026-09-11)	fails: 9 warnings, for build-dep, member and other-dep	passes
beta: cargo 1.100.0-beta.4 (7552a885e 2026-09-29)	fails: the same 9 warnings	passes
cargo 1.98.1 (797e8a9bc 2026-08-05)	fails: no lint yet, but the generated manifest also holds build-dep, member and other-dep	passes
cargo 1.93.0	not run	passes

With the fix, trybuild's own cargo test passes on nightly with CI's RUSTFLAGS="-Dwarnings -Zrandomize-layout", and on 1.98.1 and 1.93.0. cargo clippy --tests -- -Dclippy::all -Dclippy::pedantic is clean, and so is rustfmt.

Before the fix: the STDERR block of the fixture's pass test on nightly

warning: unused workspace dependency `build-dep`
  --> Cargo.toml:35:25
   |
35 | [workspace.dependencies.build-dep]
   |                         ^^^^^^^^^
   |
   = note: `cargo::unused_workspace_dependencies` is set to `warn` by default
help: consider removing the workspace dependency `build-dep`
warning: unused workspace dependency `member`
  --> Cargo.toml:44:25
   |
44 | [workspace.dependencies.member]
   |                         ^^^^^^
   |
help: consider removing the workspace dependency `member`
warning: unused workspace dependency `other-dep`
  --> Cargo.toml:47:25
   |
47 | [workspace.dependencies.other-dep]
   |                         ^^^^^^^^^
   |
help: consider removing the workspace dependency `other-dep`

pr-343-test-results.md

🤖 Generated with Claude Code

[dtolnay]

Thanks!