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| 1 | +use crate::utils::{get_trait_def_id, paths, span_lint, span_lint_and_help}; |
| 2 | +use if_chain::if_chain; |
| 3 | +use rustc_hir::def_id::DefId; |
| 4 | +use rustc_hir::{Expr, ExprKind, StmtKind}; |
| 5 | +use rustc_lint::{LateContext, LateLintPass}; |
| 6 | +use rustc_middle::ty; |
| 7 | +use rustc_middle::ty::{GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate}; |
| 8 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 9 | +use rustc_span::{BytePos, Span}; |
| 10 | + |
| 11 | +declare_clippy_lint! { |
| 12 | + /// **What it does:** Checks for functions that expect closures of type |
| 13 | + /// Fn(...) -> Ord where the implemented closure has a semi-colon |
| 14 | + /// at the end of the last statement. |
| 15 | + /// |
| 16 | + /// **Why is this bad?** Likely the semi-colon is unintentional which |
| 17 | + /// returns () instead of the result of last statement. Since () implements Ord |
| 18 | + /// it doesn't cause a compilation error |
| 19 | + /// |
| 20 | + /// **Known problems:** If returning unit is intentional, then there is no |
| 21 | + /// way of specifying this without triggering needless_return lint |
| 22 | + /// |
| 23 | + /// **Example:** |
| 24 | + /// |
| 25 | + /// ```rust |
| 26 | + /// let mut twins = vec!((1,1), (2,2)); |
| 27 | + /// twins.sort_by_key(|x| { x.1; }); |
| 28 | + /// ``` |
| 29 | + pub UNINTENTIONAL_UNIT_RETURN, |
| 30 | + nursery, |
| 31 | + "fn arguments of type Fn(...) -> Once having last statements with a semi-colon, suggesting to remove the semi-colon if it is unintentional." |
| 32 | +} |
| 33 | + |
| 34 | +declare_lint_pass!(UnintentionalUnitReturn => [UNINTENTIONAL_UNIT_RETURN]); |
| 35 | + |
| 36 | +fn get_trait_predicates_for_trait_id<'tcx>( |
| 37 | + cx: &LateContext<'tcx>, |
| 38 | + generics: GenericPredicates<'tcx>, |
| 39 | + trait_id: Option<DefId>, |
| 40 | +) -> Vec<TraitPredicate<'tcx>> { |
| 41 | + let mut preds = Vec::new(); |
| 42 | + for (pred, _) in generics.predicates { |
| 43 | + if_chain! { |
| 44 | + if let PredicateKind::Trait(poly_trait_pred, _) = pred.kind(); |
| 45 | + let trait_pred = cx.tcx.erase_late_bound_regions(&poly_trait_pred); |
| 46 | + if let Some(trait_def_id) = trait_id; |
| 47 | + if trait_def_id == trait_pred.trait_ref.def_id; |
| 48 | + then { |
| 49 | + preds.push(trait_pred); |
| 50 | + } |
| 51 | + } |
| 52 | + } |
| 53 | + preds |
| 54 | +} |
| 55 | + |
| 56 | +fn get_projection_pred<'tcx>( |
| 57 | + cx: &LateContext<'tcx>, |
| 58 | + generics: GenericPredicates<'tcx>, |
| 59 | + pred: TraitPredicate<'tcx>, |
| 60 | +) -> Option<ProjectionPredicate<'tcx>> { |
| 61 | + generics.predicates.iter().find_map(|(proj_pred, _)| { |
| 62 | + if let PredicateKind::Projection(proj_pred) = proj_pred.kind() { |
| 63 | + let projection_pred = cx.tcx.erase_late_bound_regions(proj_pred); |
| 64 | + if projection_pred.projection_ty.substs == pred.trait_ref.substs { |
| 65 | + return Some(projection_pred); |
| 66 | + } |
| 67 | + } |
| 68 | + None |
| 69 | + }) |
| 70 | +} |
| 71 | + |
| 72 | +fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Vec<(usize, String)> { |
| 73 | + let mut args_to_check = Vec::new(); |
| 74 | + if let Some(def_id) = cx.tables().type_dependent_def_id(expr.hir_id) { |
| 75 | + let fn_sig = cx.tcx.fn_sig(def_id); |
| 76 | + let generics = cx.tcx.predicates_of(def_id); |
| 77 | + let fn_mut_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().fn_mut_trait()); |
| 78 | + let ord_preds = get_trait_predicates_for_trait_id(cx, generics, get_trait_def_id(cx, &paths::ORD)); |
| 79 | + let partial_ord_preds = |
| 80 | + get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().partial_ord_trait()); |
| 81 | + // Trying to call erase_late_bound_regions on fn_sig.inputs() gives the following error |
| 82 | + // The trait `rustc::ty::TypeFoldable<'_>` is not implemented for `&[&rustc::ty::TyS<'_>]` |
| 83 | + let inputs_output = cx.tcx.erase_late_bound_regions(&fn_sig.inputs_and_output()); |
| 84 | + inputs_output |
| 85 | + .iter() |
| 86 | + .rev() |
| 87 | + .skip(1) |
| 88 | + .rev() |
| 89 | + .enumerate() |
| 90 | + .for_each(|(i, inp)| { |
| 91 | + for trait_pred in &fn_mut_preds { |
| 92 | + if_chain! { |
| 93 | + if trait_pred.self_ty() == inp; |
| 94 | + if let Some(return_ty_pred) = get_projection_pred(cx, generics, *trait_pred); |
| 95 | + then { |
| 96 | + if ord_preds.iter().any(|ord| ord.self_ty() == return_ty_pred.ty) { |
| 97 | + args_to_check.push((i, "Ord".to_string())); |
| 98 | + } else if partial_ord_preds.iter().any(|pord| pord.self_ty() == return_ty_pred.ty) { |
| 99 | + args_to_check.push((i, "PartialOrd".to_string())); |
| 100 | + } |
| 101 | + } |
| 102 | + } |
| 103 | + } |
| 104 | + }); |
| 105 | + } |
| 106 | + args_to_check |
| 107 | +} |
| 108 | + |
| 109 | +fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Span, Option<Span>)> { |
| 110 | + if_chain! { |
| 111 | + if let ExprKind::Closure(_, _fn_decl, body_id, span, _) = arg.kind; |
| 112 | + if let ty::Closure(_def_id, substs) = &cx.tables().node_type(arg.hir_id).kind; |
| 113 | + let ret_ty = substs.as_closure().sig().output(); |
| 114 | + let ty = cx.tcx.erase_late_bound_regions(&ret_ty); |
| 115 | + if ty.is_unit(); |
| 116 | + then { |
| 117 | + if_chain! { |
| 118 | + let body = cx.tcx.hir().body(body_id); |
| 119 | + if let ExprKind::Block(block, _) = body.value.kind; |
| 120 | + if block.expr.is_none(); |
| 121 | + if let Some(stmt) = block.stmts.last(); |
| 122 | + if let StmtKind::Semi(_) = stmt.kind; |
| 123 | + then { |
| 124 | + let data = stmt.span.data(); |
| 125 | + // Make a span out of the semicolon for the help message |
| 126 | + Some((span, Some(Span::new(data.hi-BytePos(1), data.hi, data.ctxt)))) |
| 127 | + } else { |
| 128 | + Some((span, None)) |
| 129 | + } |
| 130 | + } |
| 131 | + } else { |
| 132 | + None |
| 133 | + } |
| 134 | + } |
| 135 | +} |
| 136 | + |
| 137 | +impl<'tcx> LateLintPass<'tcx> for UnintentionalUnitReturn { |
| 138 | + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { |
| 139 | + if let ExprKind::MethodCall(_, _, ref args, _) = expr.kind { |
| 140 | + let arg_indices = get_args_to_check(cx, expr); |
| 141 | + for (i, trait_name) in arg_indices { |
| 142 | + if i < args.len() { |
| 143 | + match check_arg(cx, &args[i]) { |
| 144 | + Some((span, None)) => { |
| 145 | + span_lint( |
| 146 | + cx, |
| 147 | + UNINTENTIONAL_UNIT_RETURN, |
| 148 | + span, |
| 149 | + &format!( |
| 150 | + "this closure returns \ |
| 151 | + the unit type which also implements {}", |
| 152 | + trait_name |
| 153 | + ), |
| 154 | + ); |
| 155 | + }, |
| 156 | + Some((span, Some(last_semi))) => { |
| 157 | + span_lint_and_help( |
| 158 | + cx, |
| 159 | + UNINTENTIONAL_UNIT_RETURN, |
| 160 | + span, |
| 161 | + &format!( |
| 162 | + "this closure returns \ |
| 163 | + the unit type which also implements {}", |
| 164 | + trait_name |
| 165 | + ), |
| 166 | + Some(last_semi), |
| 167 | + &"probably caused by this trailing semicolon".to_string(), |
| 168 | + ); |
| 169 | + }, |
| 170 | + None => {}, |
| 171 | + } |
| 172 | + } |
| 173 | + } |
| 174 | + } |
| 175 | + } |
| 176 | +} |
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