Broken unstable lint examples in rustc book

[pitaj]

The examples for the following unstable lints are currently broken, leading to the auto-generated outputs only displaying an "unknown lint" warning:

• fuzzy_provenance_casts
• lossy_provenance_casts
• unqualified_local_imports
• test_unstable_lint

The examples in the lint doc-comments need to be updated to include enabling the respective feature for each lint. See the must_not_suspend lint docs for a correct example.

[Aditya-PS-05]

@jieyouxu , can you assign me this issue? I would love to work on this?

[ehuss]

Hm, we have code to specifically prevent this from happening, but unfortunately it is too loose.

rust/src/tools/lint-docs/src/lib.rs

Lines 485 to 488 in 8247594

	let matches: Vec<_> = msgs.iter().filter(|msg|
	matches!(&msg["rendered"], serde_json::Value::String(s) if s.contains(name)))
	.map(|msg| msg["rendered"].as_str().expect("rendered field should exist").to_string())
	.collect();

Perhaps that could be tightened up somehow to prevent this?