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An implementation for the lint described in #11721
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,176 @@ | ||
| use clippy_utils::diagnostics::span_lint_and_then; | ||
| use clippy_utils::sugg::DiagnosticExt; | ||
| use clippy_utils::ty::is_copy; | ||
| use rustc_data_structures::fx::FxIndexMap; | ||
| use rustc_errors::Applicability; | ||
| use rustc_hir::*; | ||
| use rustc_hir_typeck::expr_use_visitor as euv; | ||
| use rustc_infer::infer::TyCtxtInferExt; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_middle::mir::FakeReadCause; | ||
| use rustc_middle::ty::{self, UpvarId}; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// Checks for closures and `async` blocks where the `move` is not necessary. | ||
| /// E.g. all the values are captured by value into the closure / `async` block. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// Pedantry | ||
| /// ### Example | ||
| /// ```no_run | ||
| /// let a = String::new(); | ||
| /// let closure = move || { | ||
| /// drop(a); | ||
| /// }; | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```no_run | ||
| /// let a = String::new(); | ||
| /// let closure = || { | ||
| /// drop(a); | ||
| /// }; | ||
| /// ``` | ||
| #[clippy::version = "1.75.0"] | ||
| pub NEEDLESS_MOVE, | ||
| pedantic, | ||
| "checks for needless `move`s on closures / `async` blocks" | ||
| } | ||
|
|
||
| declare_lint_pass!(NeedlessMove => [NEEDLESS_MOVE]); | ||
|
|
||
| impl NeedlessMove { | ||
| fn check_closure<'tcx>(&self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, closure: &'tcx Closure<'tcx>) { | ||
| let CaptureBy::Value { move_kw } = closure.capture_clause else { | ||
| return; | ||
| }; | ||
|
|
||
| // Collect moved & borrowed variables from the closure, which the closure *actually* needs. | ||
| let MovedVariablesCtxt { | ||
| moved_vars, | ||
| mut captured_vars, | ||
| } = { | ||
| let mut ctx = MovedVariablesCtxt { | ||
| captured_vars: Default::default(), | ||
| moved_vars: Default::default(), | ||
| }; | ||
| let body = cx.tcx.hir().body(closure.body); | ||
| let infcx = cx.tcx.infer_ctxt().build(); | ||
| euv::ExprUseVisitor::new(&mut ctx, &infcx, closure.def_id, cx.param_env, cx.typeck_results()) | ||
| .consume_body(body); | ||
| ctx | ||
| }; | ||
|
|
||
| // Remove the captured vars which were also `move`d. | ||
| // See special case 1. below. | ||
| for (hir_id, _upvars) in moved_vars.iter() { | ||
| let Some(vars) = captured_vars.get_mut(hir_id) else { | ||
| continue; | ||
| }; | ||
|
|
||
| if vars | ||
| .iter() | ||
| .any(|(_, hir_borrow_id, _)| is_copy(cx, cx.typeck_results().node_type(*hir_borrow_id))) | ||
| { | ||
| continue; | ||
| } | ||
|
|
||
| captured_vars.remove(hir_id); | ||
| } | ||
|
|
||
| let lint = |note_msg: &'static str| { | ||
| span_lint_and_then( | ||
| cx, | ||
| NEEDLESS_MOVE, | ||
| expr.span, | ||
| "you seem to use `move`, but the `move` is unnecessary", | ||
| |diag| { | ||
| diag.suggest_remove_item(cx, move_kw, "remove the `move`", Applicability::MachineApplicable); | ||
| diag.note(note_msg); | ||
| }, | ||
| ); | ||
| }; | ||
|
|
||
| match (moved_vars.is_empty(), captured_vars.is_empty()) { | ||
| (true, true) => lint("there were no captured variables, so the `move` is unnecessary"), | ||
| (false, true) => lint("there were consumed variables, but no borrowed variables, so the `move` is unnecessary"), | ||
| (_, false) => { | ||
| // captured_vars is not empty, so `move` actually makes a difference and we | ||
| // should not remove it from this closure. | ||
| }, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for NeedlessMove { | ||
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { | ||
| if expr.span.from_expansion() { | ||
| return; | ||
| } | ||
|
|
||
| let ExprKind::Closure(closure) = &expr.kind else { | ||
| return; | ||
| }; | ||
|
|
||
| self.check_closure(cx, expr, closure); | ||
| } | ||
| } | ||
|
|
||
| struct MovedVariablesCtxt { | ||
| // for each base variable, we remember: | ||
| /// The places where it was captured (and consumed, e.g. moved into the closure). | ||
| moved_vars: FxIndexMap<HirId, Vec<UpvarId>>, | ||
| /// The places where it was captured by reference (and not consumed). | ||
| /// If this vector is not empty, then the `move` keyword makes a difference. | ||
| /// There are a few special cases though, such as: | ||
| /// 1. We also handle the case in which there's both a borrow and a move of the | ||
| /// same value into the closure, e.g.: | ||
| /// | ||
| /// ```no_run | ||
| /// let x = String::new(); | ||
| /// let closure = move || { | ||
| /// let s = x.as_str(); // L1 | ||
| /// println!("{s}"); | ||
| /// drop(x); // L2 | ||
| /// }; | ||
| /// ``` | ||
| /// | ||
| /// In this case, the `x` `String` gets moved into the closure (because of L2), but | ||
| /// it is also borrowed prior to that at L1. | ||
| /// | ||
| /// How we handle this is by removing the entries that point to `x` if it was captured | ||
| /// by value (and therefore moved into the closure). | ||
| captured_vars: FxIndexMap<HirId, Vec<(UpvarId, HirId, ty::BorrowKind)>>, | ||
| } | ||
|
|
||
| impl MovedVariablesCtxt { | ||
| fn move_common(&mut self, cmt: &euv::PlaceWithHirId<'_>, _: HirId) { | ||
| if let euv::PlaceBase::Upvar(vid) = cmt.place.base { | ||
| self.moved_vars.entry(vid.var_path.hir_id).or_default().push(vid); | ||
| } | ||
| } | ||
|
|
||
| fn borrow_common(&mut self, cmt: &euv::PlaceWithHirId<'_>, borrow_hir_id: HirId, bk: ty::BorrowKind) { | ||
| if let euv::PlaceBase::Upvar(vid) = cmt.place.base { | ||
| self.captured_vars | ||
| .entry(vid.var_path.hir_id) | ||
| .or_default() | ||
| .push((vid, borrow_hir_id, bk)); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt { | ||
| fn consume(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, hir_id: HirId) { | ||
| self.move_common(cmt, hir_id); | ||
| } | ||
|
|
||
| fn borrow(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, hir_id: HirId, bk: ty::BorrowKind) { | ||
| self.borrow_common(cmt, hir_id, bk); | ||
| } | ||
|
|
||
| fn mutate(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: HirId) {} | ||
|
|
||
| fn fake_read(&mut self, _: &rustc_hir_typeck::expr_use_visitor::PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {} | ||
| } |
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