Harden proc macro path resolution and add integration tests.

[raldone01]

This pr uses the extern crate self as trick to make proc macros behave the same way inside and outside bevy.

Objective

• Removes noise introduced by crate as in the whole bevy repo.
• Hopefully fixes rust-analyzer autocomplete is broken for some ECS types #17004.
• Hardens proc macro path resolution.

TODO

• BevyManifest needs cleanup.
• External crate dependency cargo-manifest-proc-macros needs discussion.
• Interface of cargo-manifest-proc-macros needs discussion.
• Cleanup remaining crate as.
• Add proper integration tests to the ci.

Open Questions

• What is the policy of adding an external dependency?
• cargo-manifest-proc-macros is written by me and based/inspired by the old BevyManifest implementation and bkchr/proc-macro-crate.
• Any suggestions for the api of the cargo-manifest-proc-macros crate?
• Should I lower the edition of cargo-manifest-proc-macros from 2024 to 2021?
• What do you think about the new integration test machinery I added to the ci?
  More and better integration tests can be added at a later stage.
  The goal of these integration tests is to simulate an actual separate crate that uses bevy. Ideally they would lightly touch all bevy crates.

Testing

• Needs RA test
• Needs testing from other users
• Others need to run at least cargo run -p ci integration-test and verify that they work.

[BenjaminBrienen]

😆

[BenjaminBrienen]

Great idea, just need to fix the errors

[raldone01]

I will make the ci pass coming Thursday or Friday.

[mdickopp]

When I try this branch, rust-analyzer logs this:

2025-01-17T11:44:08.66709452+01:00 ERROR Flycheck failed to run the following command: CommandHandle { program: "/home/martin/.cargo/bin/cargo", arguments: ["check", "--workspace", "--message-format=json-diagnostic-rendered-ansi", "--manifest-path", "/home/martin/tmp/bevy-rs/Cargo.toml", "--keep-going", "--all-targets"], current_dir: Some("/home/martin/tmp/bevy-rs") }, error=Cargo watcher failed, the command produced no valid metadata (exit code: ExitStatus(unix_wait_status(25856))):
error: failed to download `cargo-manifest-proc-macros v0.3.1`

Caused by:
  unable to get packages from source

Caused by:
  failed to parse manifest at `/home/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-manifest-proc-macros-0.3.1/Cargo.toml`

Caused by:
  feature `edition2024` is required

  The package requires the Cargo feature called `edition2024`, but that feature is not stabilized in this version of Cargo (1.84.0 (66221abde 2024-11-19)).
  Consider trying a newer version of Cargo (this may require the nightly release).
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2024 for more information about the status of this feature.

2025-01-17T11:44:30.350601426+01:00 ERROR Flycheck failed to run the following command: CommandHandle { program: "/home/martin/.cargo/bin/cargo", arguments: ["check", "-p", "bevy", "--example", "alien_cake_addict", "--message-format=json-diagnostic-rendered-ansi", "--manifest-path", "/home/martin/tmp/bevy-rs/Cargo.toml", "--keep-going", "--all-targets"], current_dir: Some("/home/martin/tmp/bevy-rs") }, error=Cargo watcher failed, the command produced no valid metadata (exit code: ExitStatus(unix_wait_status(25856))):
error: failed to download `cargo-manifest-proc-macros v0.3.1`

Caused by:
  unable to get packages from source

Caused by:
  failed to parse manifest at `/home/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-manifest-proc-macros-0.3.1/Cargo.toml`

Caused by:
  feature `edition2024` is required

  The package requires the Cargo feature called `edition2024`, but that feature is not stabilized in this version of Cargo (1.84.0 (66221abde 2024-11-19)).
  Consider trying a newer version of Cargo (this may require the nightly release).
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2024 for more information about the status of this feature.

Is it expected to work with stable Rust / edition 2021?

[mdickopp]

The command cargo check does not work either with Rust 1.84.0:

error: failed to download `cargo-manifest-proc-macros v0.3.1`

Caused by:
  unable to get packages from source

Caused by:
  failed to parse manifest at `/home/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-manifest-proc-macros-0.3.1/Cargo.toml`

Caused by:
  feature `edition2024` is required

  The package requires the Cargo feature called `edition2024`, but that feature is not stabilized in this version of Cargo (1.84.0 (66221abde 2024-11-19)).
  Consider trying a newer version of Cargo (this may require the nightly release).
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2024 for more information about the status of this feature.

[raldone01]

I know. Please try it with nightly for now. Clean your project first and restart rust analyzer.

I need to modify cargo-manifest-proc-macros to support older rust versions.