hir-ty: emit diagnostic for unused #[must_use] values#22239
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ChayimFriedman2 merged 1 commit intoMay 2, 2026
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| "unstable" => attr_flags.insert(AttrFlags::IS_UNSTABLE), | ||
| "deprecated" => attr_flags.insert(AttrFlags::IS_DEPRECATED), | ||
| "macro_export" => attr_flags.insert(AttrFlags::IS_MACRO_EXPORT), | ||
| "must_use" => attr_flags.insert(AttrFlags::IS_MUST_USE), |
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A possible enhancement (not necessarily in this PR) is to also have a query to fetch the must_use reason, like other queries in this file.
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| if self.validate_lints { | ||
| for stmt in &**statements { | ||
| if let &Statement::Expr { expr: stmt_expr, has_semi: true } = stmt { | ||
| self.check_unused_must_use(stmt_expr); | ||
| } | ||
| } | ||
| } |
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Instead of looping over the expressions twice, please combine them with the run below in this function. It might make sense to extract the existing handling to a function.
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Address review feedback on rust-lang#22239: combine the must-use loop and the non-exhaustive-let loop into a single pass over `statements`, and lift the existing handling into a dedicated `check_non_exhaustive_let` method. `check_unused_must_use` and `check_non_exhaustive_let` now return `Option<BodyValidationDiagnostic>`; the caller pushes the result. This keeps `&self.infcx` (held by `MatchCheckCtx`) compatible with the mutable borrow on `self.diagnostics` via field-level split borrows.
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Addressed the expression looping . . . let me know if adequate |
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Address review feedback on rust-lang#22239: combine the must-use loop and the non-exhaustive-let loop into a single pass over `statements`, and lift the existing handling into a dedicated `check_non_exhaustive_let` method. `check_unused_must_use` and `check_non_exhaustive_let` now return `Option<BodyValidationDiagnostic>`; the caller pushes the result. This keeps `&self.infcx` (held by `MatchCheckCtx`) compatible with the mutable borrow on `self.diagnostics` via field-level split borrows.
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Address review feedback on rust-lang#22239: combine the must-use loop and the non-exhaustive-let loop into a single pass over `statements`, and lift the existing handling into a dedicated `check_non_exhaustive_let` method. `check_unused_must_use` and `check_non_exhaustive_let` now return `Option<BodyValidationDiagnostic>`; the caller pushes the result. This keeps `&self.infcx` (held by `MatchCheckCtx`) compatible with the mutable borrow on `self.diagnostics` via field-level split borrows.
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Address review feedback on rust-lang/rust-analyzer#22239: combine the must-use loop and the non-exhaustive-let loop into a single pass over `statements`, and lift the existing handling into a dedicated `check_non_exhaustive_let` method. `check_unused_must_use` and `check_non_exhaustive_let` now return `Option<BodyValidationDiagnostic>`; the caller pushes the result. This keeps `&self.infcx` (held by `MatchCheckCtx`) compatible with the mutable borrow on `self.diagnostics` via field-level split borrows.
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ExprValidator::check_unused_must_use previously matched only Expr::Call and Expr::MethodCall directly on the expression of a Statement::Expr with semicolon. This left several stmt-with-semi cases unwarned: blocks whose tail is a #[must_use] call, unsafe-blocks, if/else arms, match arms, and const blocks.
Refactors check_unused_must_use to walk into Expr::Block { tail }, Expr::Unsafe { tail }, Expr::If { then_branch, else_branch }, Expr::Match { arms }, and Expr::Const(inner) before applying the existing leaf check (callee or method #[must_use] attribute, or #[must_use] ADT return type). The diagnostic stays at the leaf call so the span points to the actual must_use producer rather than the wrapping block.
Adds ide-diagnostics tests covering each new container case.
Follow-up to rust-lang#22239.
Signed-off-by: Onyeka Obi <softwareengineerasaservant@isurvivable.cv>
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ExprValidator::check_unused_must_use previously matched only Expr::Call and Expr::MethodCall directly on the expression of a Statement::Expr with semicolon. This left several stmt-with-semi cases unwarned: blocks whose tail is a #[must_use] call, unsafe-blocks, if/else arms, match arms, and const blocks.
Refactors check_unused_must_use to walk into Expr::Block { tail }, Expr::Unsafe { tail }, Expr::If { then_branch, else_branch }, Expr::Match { arms }, and Expr::Const(inner) before applying the existing leaf check (callee or method #[must_use] attribute, or #[must_use] ADT return type). The diagnostic stays at the leaf call so the span points to the actual must_use producer rather than the wrapping block.
Adds ide-diagnostics tests covering each new container case.
Follow-up to rust-lang/rust-analyzer#22239.
Signed-off-by: Onyeka Obi <softwareengineerasaservant@isurvivable.cv>
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Adds the unused_must_use lint that warns when the result of a call or method call is dropped despite the callee or its return type carrying #[must_use].
must_usesymbol.#[must_use](PathMeta) and#[must_use = "reason"](KeyValueMeta).