Fix/clarify inert/active attributes, and attribute sequence.

Open
#565 3 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Documentation
Clarity
Needs clarification
Activity status
Stale
Tech stack
rust
Domain
compilers, documentation

Research direction

Start by reviewing the linked pull-request review and issue comment, then trace the relevant attribute-processing behavior in rustc as requested. Establish when attributes are visible, removed, or pruned, and how processing order works. Done means the Rust Reference clearly documents the inert/active distinction, attribute order, macro visibility, and cfg pruning.

Written by the indexing model from the issue text.

Description

A-attributes

The inert/active attribute description is not be correct. The following comment needs to be incorporated: https://github.com/rust-lang-nursery/reference/pull/537#pullrequestreview-218090880

However, I think the inert/active distinction is subtle and should have more clarification. It is possible to "see" an active attribute based on the point in time during compilation (for example, an attribute macro placed before #[test] sees the test attribute, it has not been removed, yet).

Also, to me it seems like like cfg and cfg_attr aren't always active. If the predicate is true, they are clearly visible from attribute macros, so they have not been removed. This comment implies that things are broken.

I would like to know how I can validate this inert/active distinction by reading the rustc code. It is not tracked in any data structure I can see, and I do not know through which mechanism an attribute removes itself. Otherwise I feel like I am shooting in the dark trying to document this.

Also I think the order that attributes are processed and when attributes remove themselves should be documented. For example, do attribute macros see derive macros (yes, the derive has not been removed, yet). What is the significance of the order that attributes are listed? (Presumably they are processed top-down?) Attribute macros seem to be removed only after they are processed (an attribute macro sees the attributes below it, but not above it). When is cfg pruning done (pretty early)? In general I think the order attributes are processed and when attributes remove themselves should be documented.

Dominant language
Rust
Stars
1.6k
Forks
607
Avg merge
1d 1h
Merged PRs (30d)
12

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from rust-lang/reference

All issues in rust-lang/reference

Similar issues

More Rust issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.