Panic on use of libraries with proc-macro examples

[OliverKillane]

Problem

Cargo is panicking on valid examples targets.

• examples crate-type field

Minimised example is here

thread 'main' panicked at src/cargo/core/resolver/features.rs:323:14:
activated_features for invalid package: features did not find PackageId { name: "library", version: "0.1.0", source: "/home/oliverkillane/files/bug-reports/cargo-proc-macro-examples/library" } NormalOrDev
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Discovered in the wild when using @CraftSpider 's chumsky-proc

Steps

git clone git@github.com:OliverKillane/bug-reports.git
cd bug-reports/cargo-proc-macro-examples/application/
cargo check

Possible Solution(s)

No response

Notes

Similar error to #10593 but different cause.

Version

cargo 1.77.1 (e52e36006 2024-03-26)
release: 1.77.1
commit-hash: e52e360061cacbbeac79f7f1215a7a90b6f08442
commit-date: 2024-03-26
host: x86_64-unknown-linux-gnu
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.5.0-DEV (sys:0.4.70+curl-8.5.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Ubuntu 22.04 (jammy) [64-bit]

[ehuss]

The linked repository is 404. Is it perhaps private?

What is the output you are seeing?

[OliverKillane]

The linked repository is 404. Is it perhaps private?

Fixed!

[heisen-li]

@rustbot label A-features2 A-crate-types

[torhovland]

Reproduced on master.

@rustbot label +Command-check, +S-needs-mentor, -S-triage

[torhovland]

Here's a minimal test case:

use cargo_test_support::project;

#[cargo_test]
fn issue_13726() {
    let p = project()
        .file(
            "Cargo.toml",
            r#"
                [package]
                name = "application"
                edition = "2021"
                
                [dependencies]
                library = { path = "library" }
            "#,
        )
        .file("src/main.rs", "fn main() {}")
        .file(
            "library/Cargo.toml",
            r#"
                [package]
                name = "library"
                
                [[example]]
                name = "foo"
                proc-macro = true
                crate-type = ["proc-macro"]
            "#,
        )
        .file("library/src/lib.rs", "")
        .file("library/examples/foo.rs", "")
        .build();

    p.cargo("check").run();
}

[weihanglo]

Thanks for the minimal test case. I went ahead and edited it a bit. According to The Cargo Book, only [lib] can have proc-macro set. However, there is no warning if set. This discrepancy should belong to another issue though. I honestly don't know why it was designed like that.

Anyway, the updated version aligns to the original reproduction from the issue author, and they have the same bad behavior.

[weihanglo]

Hmm… I am seeing odd behavior. Maybe we should add both proc-macro = true and crate-type = ["proc-macro"] for the minimal reproduction for completeness.