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Auto merge of #4823 - Areredify:must_use_res, r=flip1995
Add `let_underscore_must_use` lint changelog: closes #4812 , added a new `let_underscore_must_use` lint, moved `is_must_use_ty` to utils, added `is_must_use_fn` util function
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,62 @@ | ||
| use if_chain::if_chain; | ||
| use rustc::declare_lint_pass; | ||
| use rustc::hir::*; | ||
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; | ||
| use rustc_session::declare_tool_lint; | ||
|
|
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| use crate::utils::{is_must_use_func_call, is_must_use_ty, span_help_and_lint}; | ||
|
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| declare_clippy_lint! { | ||
| /// **What it does:** Checks for `let _ = <expr>` | ||
| /// where expr is #[must_use] | ||
| /// | ||
| /// **Why is this bad?** It's better to explicitly | ||
| /// handle the value of a #[must_use] expr | ||
| /// | ||
| /// **Known problems:** None. | ||
| /// | ||
| /// **Example:** | ||
| /// ```rust | ||
| /// fn f() -> Result<u32, u32> { | ||
| /// Ok(0) | ||
| /// } | ||
| /// | ||
| /// let _ = f(); | ||
| /// // is_ok() is marked #[must_use] | ||
| /// let _ = f().is_ok(); | ||
| /// ``` | ||
| pub LET_UNDERSCORE_MUST_USE, | ||
| restriction, | ||
| "non-binding let on a #[must_use] expression" | ||
| } | ||
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| declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE]); | ||
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| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore { | ||
| fn check_stmt(&mut self, cx: &LateContext<'_, '_>, stmt: &Stmt) { | ||
| if_chain! { | ||
| if let StmtKind::Local(ref local) = stmt.kind; | ||
| if let PatKind::Wild = local.pat.kind; | ||
| if let Some(ref init) = local.init; | ||
| then { | ||
| if is_must_use_ty(cx, cx.tables.expr_ty(init)) { | ||
| span_help_and_lint( | ||
| cx, | ||
| LET_UNDERSCORE_MUST_USE, | ||
| stmt.span, | ||
| "non-binding let on an expression with #[must_use] type", | ||
| "consider explicitly using expression value" | ||
| ) | ||
| } else if is_must_use_func_call(cx, init) { | ||
| span_help_and_lint( | ||
| cx, | ||
| LET_UNDERSCORE_MUST_USE, | ||
| stmt.span, | ||
| "non-binding let on a result of a #[must_use] function", | ||
| "consider explicitly using function result" | ||
| ) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| #![warn(clippy::let_underscore_must_use)] | ||
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| #[must_use] | ||
| fn f() -> u32 { | ||
| 0 | ||
| } | ||
|
|
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| fn g() -> Result<u32, u32> { | ||
| Ok(0) | ||
| } | ||
|
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| #[must_use] | ||
| fn l<T>(x: T) -> T { | ||
| x | ||
| } | ||
|
|
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| fn h() -> u32 { | ||
| 0 | ||
| } | ||
|
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| struct S {} | ||
|
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| impl S { | ||
| #[must_use] | ||
| pub fn f(&self) -> u32 { | ||
| 0 | ||
| } | ||
|
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| pub fn g(&self) -> Result<u32, u32> { | ||
| Ok(0) | ||
| } | ||
|
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| fn k(&self) -> u32 { | ||
| 0 | ||
| } | ||
|
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| #[must_use] | ||
| fn h() -> u32 { | ||
| 0 | ||
| } | ||
|
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| fn p() -> Result<u32, u32> { | ||
| Ok(0) | ||
| } | ||
| } | ||
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| trait Trait { | ||
| #[must_use] | ||
| fn a() -> u32; | ||
| } | ||
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| impl Trait for S { | ||
| fn a() -> u32 { | ||
| 0 | ||
| } | ||
| } | ||
|
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| fn main() { | ||
| let _ = f(); | ||
| let _ = g(); | ||
| let _ = h(); | ||
| let _ = l(0_u32); | ||
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| let s = S {}; | ||
|
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| let _ = s.f(); | ||
| let _ = s.g(); | ||
| let _ = s.k(); | ||
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| let _ = S::h(); | ||
| let _ = S::p(); | ||
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| let _ = S::a(); | ||
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| let _ = if true { Ok(()) } else { Err(()) }; | ||
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| let a = Result::<(), ()>::Ok(()); | ||
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| let _ = a.is_ok(); | ||
|
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| let _ = a.map(|_| ()); | ||
|
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| let _ = a; | ||
| } |
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