Commit 6e8d426

committed

Doc: clarify priority of lint level sources

This updates the rustc book to clearly document how conflicting lint configurations are resolved across different sources, including command-line flags, crate-level attributes, in-line attributes, and `--cap-lints`. It also explains the special behavior of `forbid` and `force_warn`.

1 parent 449c801 commit 6e8d426Copy full SHA for 6e8d426

File tree

1 file changed

+53

-1

lines changed

src/doc/rustc/src/lints
- levels.md

1 file changed

+53

-1

lines changed

`‎src/doc/rustc/src/lints/levels.md`

Lines changed: 53 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -330,4 +330,56 @@ $`
`330`	`330`
`331`	`331`	This feature is used heavily by Cargo; it will pass `--cap-lints allow` when
`332`	`332`	`compiling your dependencies, so that if they have any warnings, they do not`
`333`		`-pollute the output of your build.`
	`333`	+pollute the output of your build. However, note that `--cap-lints allow` does not override lints marked as `force-warn`.
	`334`	`+`
	`335`	`+## Priority of Lint Level Sources`
	`336`	`+`
	`337`	+Rust allows setting lint levels (`allow`, `warn`, `deny`, etc.) through various sources:
	`338`	`+`
	`339`	+- Attributes (`#[allow(...)]`, `#![deny(...)]`, etc.)
	`340`	+- Command-line options (e.g., `--cap-lints`, `-A unused_variables`)
	`341`	`+`
	`342`	`+These mechanisms can interact in subtle ways, the compiler resolves conflicts based on the source’s scope and strength.`
	`343`	`+`
	`344`	+### Priority of sources (`allow`, `warn`, and `deny`)
	`345`	`+`
	`346`	`+For standard lint levels, the most specific scope takes precedence.`
	`347`	`+`
	`348`	+For example, the following allows the `unused-variables` lint, because it has a more specific scope:
	`349`	`+`
	`350`	+```rust
	`351`	`+#![deny(unused_variables)]`
	`352`	`+`
	`353`	`+#[allow(unused_variables)]`
	`354`	`+fn main() {`
	`355`	`+ let x = 42; // Allow wins`
	`356`	`+}`
	`357`	+```
	`358`	`+`
	`359`	+### Priority of sources (`force-warn`and `forbid`)
	`360`	`+`
	`361`	`+Special lint levels take precedence over standard levels. When multiple special levels are in effect, the least specific (outermost) scope takes precedence.`
	`362`	`+`
	`363`	`+For example, consider the following:`
	`364`	`+`
	`365`	+```rust
	`366`	`+#[forbid(unused_variables)]`
	`367`	`+fn main() {`
	`368`	`+ let x = 42; // Allow wins`
	`369`	`+}`
	`370`	+```
	`371`	`+`
	`372`	+If we compile it with `--force-warn unused_variables`:
	`373`	`+`
	`374`	+```bash
	`375`	`+$ rustc --force-warn unused_variables lib.rs`
	`376`	+warning: unused variable: `x`
	`377`	`+ --> lib.rs:3:9`
	`378`	`+ \|`
	`379`	`+40 \| let x = 42;`
	`380`	+ \| ^ help: if this is intentional, prefix it with an underscore: `_x`
	`381`	`+ \|`
	`382`	+ = note: requested on the command line with `--force-warn unused-variables`
	`383`	`+`
	`384`	`+warning: 1 warning emitted`
	`385`	+```

0 commit comments

Comments

(0)

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commit 6e8d426

File tree

1 file changed

1 file changed

`‎src/doc/rustc/src/lints/levels.md`

0 commit comments