`maybe a missing crate` with `workspace` when `edition` is not declared

[bukowa]

Problem

$ cargo build
   Compiling package3 v0.1.0 (\root\package3)
error[E0432]: unresolved import `ignore`                                                                                                                                     
 --> package3\src\tree.rs:4:5
  |
4 | use ignore::{DirEntry, Error, Walk, WalkBuilder};
  |     ^^^^^^ maybe a missing crate `ignore`?
  |
  = help: consider adding `extern crate ignore` to use the `ignore` crate

error[E0432]: unresolved import `serde`

Steps

# /root/Cargo.toml
[workspace]
resolver = "2"
members = [
    "package1", "package2", "package3",
]

# /root/package3
[package]
name = "package3"
version = "0.1.0"

[dependencies]
ignore = "0.4.22"
serde = { version = "1.0.203", features = ["derive"] }

Working Solution(s)

Add edition = "2021"

# /root/package3
[package]
name = "package3"
version = "0.1.0"
edition = "2021"

Notes

Better information would be helpful.

Version

cargo 1.79.0 (ffa9cf99a 2024-06-03)

[bukowa]

#14023

[weihanglo]

   = help: consider adding `extern crate ignore` to use the `ignore` crate

The rust compiler already gave a help message, so people do get a hint for fixing that compile error.

Note that if a package was created by a newer cargo, the package.edition should be set to the latest stable edition (2021 as of now). I would consider missing edition as a deliberate choice and won't bother users with any further warning. See

• feat(toml): Warn on unset Edition #13505 (comment)
• fix(toml): Don't warn on unset Edition if only 2015 is compatible #13533

You'll get a warning if package.rust-version is set as a version greather than 1.30.

[epage]

Is that output complete? In #13505 (1.78), we warn on unset edition.

[epage]

Also, this explicitly calls out that a workspace was used but this should behave the same without it. Can you confirm if there is something different with workspaces?

[epage]

Rustc giving a hint to specify a new edition would be worth considering but that would be for their repo, and their decision to make.

[weihanglo]

I saw what went wrong. rust_version is None here because it doesn't take the current toolchain version into account.

cargo/src/cargo/util/toml/mod.rs

Line 1133 in ac8c6ab

let msrv_edition = if let Some(pkg_msrv) = &rust_version {

There are some ways to fix this:

• Warn if both rust-version and edition are missing
• Make package.rust_version aware of toolchain version during to_real_manifest

@epage which do you like?

[bukowa]

Is that output complete? In #13505 (1.78), we warn on unset edition.

https://github.com/bukowa/rustrover-compilebug/tree/8d684228275dacc9d6a6befc53bcf192c3a27b41

$ cargo build
   Compiling package2 v0.1.0 (C:\Users\buk\RustroverProjects\rustrover-compilebug\package2)
error[E0432]: unresolved import `serde`                                                                                                                                                        
 --> package2\src\lib.rs:1:5
  |
1 | use serde::Serialize;
  |     ^^^^^ maybe a missing crate `serde`?
  |
  = help: consider adding `extern crate serde` to use the `serde` crate

For more information about this error, try `rustc --explain E0432`.                                                                                                                            
error: could not compile `package2` (lib) due to 1 previous error

$ cargo version
cargo 1.79.0 (ffa9cf99a 2024-06-03)

[weihanglo]

I saw what went wrong. rust_version is None here because it doesn't take the current toolchain version into account.

cargo/src/cargo/util/toml/mod.rs

Line 1133 in ac8c6ab

let msrv_edition = if let Some(pkg_msrv) = &rust_version {

There are some ways to fix this:

* Warn if both `rust-version` and `edition` are missing

* Make `package.rust_version` aware of toolchain version during `to_real_manifest`

@epage which do you like?

Probably the first one? People only get the warning on 1.78 or later, so it is sufficent for Cargo to know that they are already on a newer toolchain. They can alwasy set the package.rust-version field to silent it.

[bukowa]

@epage which do you like?

As a new user playing around with rust and workspaces, not understanding how everything fits together, I would expect a message that allows me to track down why this issue arises.