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Move lint level source explanation to the bottom So, uhhhhh r? `@estebank` ## User-facing change "note: `#[warn(...)]` on by default" and such are moved to the bottom of the diagnostic: ```diff - = note: `#[warn(unsupported_calling_conventions)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! = note: for more information, see issue #87678 <https://github.com/rust-lang/rust/issues/87678> + = note: `#[warn(unsupported_calling_conventions)]` on by default ``` Why warning is enabled is the least important thing, so it shouldn't be the first note the user reads, IMO. ## Developer-facing change `struct_span_lint` and similar methods have a different signature. Before: `..., impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>)` After: `..., impl Into<DiagnosticMessage>, impl for<'a, 'b> FnOnce(&'b mut DiagnosticBuilder<'a, ()>) -> &'b mut DiagnosticBuilder<'a, ()>` The reason for this is that `struct_span_lint` needs to edit the diagnostic _after_ `decorate` closure is called. This also makes lint code a little bit nicer in my opinion. Another option is to use `impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>) -> DiagnosticBuilder<'a, ()>` altough I don't _really_ see reasons to do `let lint = lint.build(message)` everywhere. ## Subtle problem By moving the message outside of the closure (that may not be called if the lint is disabled) `format!(...)` is executed earlier, possibly formatting `Ty` which may call a query that trims paths that crashes the compiler if there were no warnings... I don't think it's that big of a deal, considering that we move from `format!(...)` to `fluent` (which is lazy by-default) anyway, however this required adding a workaround which is unfortunate. ## P.S. I'm sorry, I do not how to make this PR smaller/easier to review. Changes to the lint API affect SO MUCH 😢 |
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For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.