61 lines
2.0 KiB
Rust
61 lines
2.0 KiB
Rust
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//! Basic checks for `unit_bindings` lint.
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//!
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//! The `unit_bindings` lint tries to detect cases like `let list = list.sort()`. The lint will
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//! trigger on bindings that have the unit `()` type **except** if:
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//!
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//! - The user wrote `()` on either side, i.e.
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//! - `let () = <expr>;` or `let <expr> = ();`
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//! - `let _ = ();`
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//! - The binding occurs within macro expansions, e.g. `foo!();`.
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//! - The user explicitly provided type annotations, e.g. `let x: () = <expr>`.
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//!
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//! Examples where the lint *should* fire on include:
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//!
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//! - `let _ = <expr>;`
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//! - `let pat = <expr>;`
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//! - `let _pat = <expr>;`
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//@ revisions: default_level deny_level
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//@[default_level] check-pass (`unit_bindings` is currently allow-by-default)
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#![allow(unused)]
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#![cfg_attr(deny_level, deny(unit_bindings))]
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// The `list` binding below should trigger the lint if it's not contained in a macro expansion.
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macro_rules! expands_to_sus {
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() => {
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let mut v = [1, 2, 3];
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let list = v.sort();
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}
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}
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// No warning for `y` and `z` because it is provided as type parameter.
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fn ty_param_check<T: Copy>(x: T) {
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let y = x;
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let z: T = x;
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}
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fn main() {
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// No warning if user explicitly wrote `()` on either side.
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let expr = ();
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let () = expr;
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let _ = ();
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// No warning if user explicitly annotates the unit type on the binding.
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let pat: () = expr;
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// No warning for let bindings with unit type in macro expansions.
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expands_to_sus!();
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// No warning for unit bindings in generic fns.
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ty_param_check(());
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let _ = expr; //[deny_level]~ ERROR binding has unit type
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let pat = expr; //[deny_level]~ ERROR binding has unit type
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let _pat = expr; //[deny_level]~ ERROR binding has unit type
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let mut v = [1, 2, 3];
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let list = v.sort(); //[deny_level]~ ERROR binding has unit type
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// Limitation: the lint currently does not fire on nested unit LHS bindings, i.e.
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// this will not currently trigger the lint.
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let (nested, _) = (expr, 0i32);
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}
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