cargo feature confusion in workspaces

[dvc94ch]

Problem

here is a minimal repro case: https://github.com/dvc94ch/cargo-bug

fails to build when in an empty workspace but builds when not in a workspace

Steps

[workspace]
members = ["a"]

[package]
name = "a"
version = "0.1.0"
edition = "2021"

[target.'cfg(not(target_family = "wasm"))'.dependencies]
surf = { version = "2.3.2", default-features = false, features = ["h1-client-rustls"] }

[target.'cfg(target_family = "wasm")'.dependencies]
surf = { version = "2.3.2", default-features = false, features = ["wasm-client"] }

Possible Solution(s)

No response

Notes

No response

Version

cargo version --verbose
cargo 1.65.0 (4bc8f24d3 2022-10-20)
release: 1.65.0
commit-hash: 4bc8f24d3e899462e43621aab981f6383a370365
commit-date: 2022-10-20
host: x86_64-unknown-linux-gnu
libgit2: 1.5.0 (sys:0.15.0 vendored)
libcurl: 7.83.1-DEV (sys:0.4.55+curl-7.83.1 vendored ssl:OpenSSL/1.1.1q)
os: Arch Linux [64-bit]

[epage]

Could you fill out more details, for example

• Steps for seeing what you mean by "empty workspace" and "non empty workspace"
• Error output

[dvc94ch]

updated the issue with two Cargo.toml's that cause the issue. the error is that it does not fail to build when the root Cargo.toml is removed, but simply adding the crate to a workspace, even if it's the only crate in the workspace, makes cargo unable to build the crate.

[dvc94ch]

Seems like adding the crate to the workspace causes both the h1-client-rustls and wasm-client features to be enabled, but only one should be enabled for any given build as they're mutually exclusive.

[epage]

So reproduction steps are

1. Clone the repo
2. cargo build --manifest-path a/Cargo.toml, see it fail
3. rm Cargo.toml
4. cargo build --manifest-path a/Cargo.toml, see it succeed?

Is that correct?

And can you copy/paste the error output message?

[dvc94ch]

Yes, your steps reproduce the issue.

The error is a generic build error:

cargo check --manifest-path a/Cargo.toml
    Checking surf v2.3.2
error[E0432]: unresolved import `http_client::wasm`
  --> /home/dvc/.cargo/registry/src/github.com-1ecc6299db9ec823/surf-2.3.2/src/client.rs:15:26
   |
15 |         use http_client::wasm::WasmClient as DefaultClient;
   |                          ^^^^ could not find `wasm` in `http_client`

For more information about this error, try `rustc --explain E0432`.
error: could not compile `surf` due to previous error

[epage]

Likely, the difference between workspace or not is in which resolver is being used.

When you set edition = "2021", you are opting in to resolver v2.

The resolver is determined at the workspace level but defaults to the package's edition when it is present in the root crate. For a virtual workspace (no package in it), we are stuck defaulting to workspace.resolver = "1" to avoid breaking compatibility. Adding workspace.resolver = "2" to the workspace should make it behave like the non-workspace case.

Work has started on trying to steer people towards this in documentation (#10625) and providing warnings (#10910)

[dvc94ch]

ah this does fix the problem. the mentioned PR's would have indeed prevented the issue. thanks