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new lint: redundant_locals
#10885
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new lint: redundant_locals
#10885
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,103 @@ | ||
| use clippy_utils::diagnostics::span_lint_and_help; | ||
| use clippy_utils::is_from_proc_macro; | ||
| use clippy_utils::ty::needs_ordered_drop; | ||
| use rustc_hir::def::Res; | ||
| use rustc_hir::{BindingAnnotation, ByRef, Expr, ExprKind, HirId, Local, Node, Pat, PatKind, QPath}; | ||
| use rustc_lint::{LateContext, LateLintPass, LintContext}; | ||
| use rustc_middle::lint::in_external_macro; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
| use rustc_span::symbol::Ident; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// Checks for redundant redefinitions of local bindings. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// Redundant redefinitions of local bindings do not change behavior and are likely to be unintended. | ||
| /// | ||
| /// Note that although these bindings do not affect your code's meaning, they _may_ affect `rustc`'s stack allocation. | ||
| /// | ||
| /// ### Example | ||
| /// ```rust | ||
| /// let a = 0; | ||
| /// let a = a; | ||
| /// | ||
| /// fn foo(b: i32) { | ||
| /// let b = b; | ||
| /// } | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// let a = 0; | ||
| /// // no redefinition with the same name | ||
| /// | ||
| /// fn foo(b: i32) { | ||
| /// // no redefinition with the same name | ||
| /// } | ||
| /// ``` | ||
| #[clippy::version = "1.72.0"] | ||
| pub REDUNDANT_LOCALS, | ||
| correctness, | ||
| "redundant redefinition of a local binding" | ||
| } | ||
| declare_lint_pass!(RedundantLocals => [REDUNDANT_LOCALS]); | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for RedundantLocals { | ||
| fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) { | ||
| if_chain! { | ||
| // the pattern is a single by-value binding | ||
| if let PatKind::Binding(BindingAnnotation(ByRef::No, mutability), _, ident, None) = local.pat.kind; | ||
| // the binding is not type-ascribed | ||
| if local.ty.is_none(); | ||
| // the expression is a resolved path | ||
| if let Some(expr) = local.init; | ||
| if let ExprKind::Path(qpath @ QPath::Resolved(None, path)) = expr.kind; | ||
| // the path is a single segment equal to the local's name | ||
| if let [last_segment] = path.segments; | ||
| if last_segment.ident == ident; | ||
| // resolve the path to its defining binding pattern | ||
| if let Res::Local(binding_id) = cx.qpath_res(&qpath, expr.hir_id); | ||
| if let Node::Pat(binding_pat) = cx.tcx.hir().get(binding_id); | ||
| // the previous binding has the same mutability | ||
| if find_binding(binding_pat, ident).unwrap().1 == mutability; | ||
| // the local does not affect the code's drop behavior | ||
| if !affects_drop_behavior(cx, binding_id, local.hir_id, expr); | ||
| // the local is user-controlled | ||
| if !in_external_macro(cx.sess(), local.span); | ||
| if !is_from_proc_macro(cx, expr); | ||
| then { | ||
| span_lint_and_help( | ||
| cx, | ||
| REDUNDANT_LOCALS, | ||
| vec![binding_pat.span, local.span], | ||
| "redundant redefinition of a binding", | ||
| None, | ||
| &format!("remove the redefinition of `{ident}`"), | ||
| ); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Find the annotation of a binding introduced by a pattern, or `None` if it's not introduced. | ||
| fn find_binding(pat: &Pat<'_>, name: Ident) -> Option<BindingAnnotation> { | ||
| let mut ret = None; | ||
|
|
||
| pat.each_binding_or_first(&mut |annotation, _, _, ident| { | ||
| if ident == name { | ||
| ret = Some(annotation); | ||
| } | ||
| }); | ||
|
|
||
| ret | ||
| } | ||
|
|
||
| /// Check if a rebinding of a local affects the code's drop behavior. | ||
| fn affects_drop_behavior<'tcx>(cx: &LateContext<'tcx>, bind: HirId, rebind: HirId, rebind_expr: &Expr<'tcx>) -> bool { | ||
| let hir = cx.tcx.hir(); | ||
|
|
||
| // the rebinding is in a different scope than the original binding | ||
| // and the type of the binding cares about drop order | ||
| hir.get_enclosing_scope(bind) != hir.get_enclosing_scope(rebind) | ||
| && needs_ordered_drop(cx, cx.typeck_results().expr_ty(rebind_expr)) | ||
| } | ||
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