src/tools/clippy/clippy_lints/src/manual_retain.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::ty::is_type_diagnostic_item;
   4 use clippy_utils::{get_parent_expr, match_def_path, paths, SpanlessEq};
   5 use clippy_utils::{meets_msrv, msrvs};
   6 use rustc_errors::Applicability;
   7 use rustc_hir as hir;
   8 use rustc_hir::def_id::DefId;
   9 use rustc_hir::ExprKind::Assign;
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_semver::RustcVersion;
  12 use rustc_session::{declare_tool_lint, impl_lint_pass};
  13 use rustc_span::symbol::sym;
  14
  15 const ACCEPTABLE_METHODS: [&[&str]; 4] = [
  16     &paths::HASHSET_ITER,
  17     &paths::BTREESET_ITER,
  18     &paths::SLICE_INTO,
  19     &paths::VEC_DEQUE_ITER,
  20 ];
  21 const ACCEPTABLE_TYPES: [(rustc_span::Symbol, Option<RustcVersion>); 6] = [
  22     (sym::BTreeSet, Some(msrvs::BTREE_SET_RETAIN)),
  23     (sym::BTreeMap, Some(msrvs::BTREE_MAP_RETAIN)),
  24     (sym::HashSet, Some(msrvs::HASH_SET_RETAIN)),
  25     (sym::HashMap, Some(msrvs::HASH_MAP_RETAIN)),
  26     (sym::Vec, None),
  27     (sym::VecDeque, None),
  28 ];
  29
  30 declare_clippy_lint! {
  31     /// ### What it does
  32     /// Checks for code to be replaced by `.retain()`.
  33     /// ### Why is this bad?
  34     /// `.retain()` is simpler and avoids needless allocation.
  35     /// ### Example
  36     /// ```rust
  37     /// let mut vec = vec![0, 1, 2];
  38     /// vec = vec.iter().filter(|&x| x % 2 == 0).copied().collect();
  39     /// vec = vec.into_iter().filter(|x| x % 2 == 0).collect();
  40     /// ```
  41     /// Use instead:
  42     /// ```rust
  43     /// let mut vec = vec![0, 1, 2];
  44     /// vec.retain(|x| x % 2 == 0);
  45     /// ```
  46     #[clippy::version = "1.63.0"]
  47     pub MANUAL_RETAIN,
  48     perf,
  49     "`retain()` is simpler and the same functionalitys"
  50 }
  51
  52 pub struct ManualRetain {
  53     msrv: Option<RustcVersion>,
  54 }
  55
  56 impl ManualRetain {
  57     #[must_use]
  58     pub fn new(msrv: Option<RustcVersion>) -> Self {
  59         Self { msrv }
  60     }
  61 }
  62
  63 impl_lint_pass!(ManualRetain => [MANUAL_RETAIN]);
  64
  65 impl<'tcx> LateLintPass<'tcx> for ManualRetain {
  66     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
  67         if let Some(parent_expr) = get_parent_expr(cx, expr)
  68             && let Assign(left_expr, collect_expr, _) = &parent_expr.kind
  69             && let hir::ExprKind::MethodCall(seg, _, _) = &collect_expr.kind
  70             && seg.args.is_none()
  71             && let hir::ExprKind::MethodCall(_, [target_expr], _) = &collect_expr.kind
  72             && let Some(collect_def_id) = cx.typeck_results().type_dependent_def_id(collect_expr.hir_id)
  73             && match_def_path(cx, collect_def_id, &paths::CORE_ITER_COLLECT) {
  74             check_into_iter(cx, parent_expr, left_expr, target_expr, self.msrv);
  75             check_iter(cx, parent_expr, left_expr, target_expr, self.msrv);
  76             check_to_owned(cx, parent_expr, left_expr, target_expr, self.msrv);
  77         }
  78     }
  79
  80     extract_msrv_attr!(LateContext);
  81 }
  82
  83 fn check_into_iter(
  84     cx: &LateContext<'_>,
  85     parent_expr: &hir::Expr<'_>,
  86     left_expr: &hir::Expr<'_>,
  87     target_expr: &hir::Expr<'_>,
  88     msrv: Option<RustcVersion>,
  89 ) {
  90     if let hir::ExprKind::MethodCall(_, [into_iter_expr, _], _) = &target_expr.kind
  91         && let Some(filter_def_id) = cx.typeck_results().type_dependent_def_id(target_expr.hir_id)
  92         && match_def_path(cx, filter_def_id, &paths::CORE_ITER_FILTER)
  93         && let hir::ExprKind::MethodCall(_, [struct_expr], _) = &into_iter_expr.kind
  94         && let Some(into_iter_def_id) = cx.typeck_results().type_dependent_def_id(into_iter_expr.hir_id)
  95         && match_def_path(cx, into_iter_def_id, &paths::CORE_ITER_INTO_ITER)
  96         && match_acceptable_type(cx, left_expr, msrv)
  97         && SpanlessEq::new(cx).eq_expr(left_expr, struct_expr) {
  98         suggest(cx, parent_expr, left_expr, target_expr);
  99     }
 100 }
 101
 102 fn check_iter(
 103     cx: &LateContext<'_>,
 104     parent_expr: &hir::Expr<'_>,
 105     left_expr: &hir::Expr<'_>,
 106     target_expr: &hir::Expr<'_>,
 107     msrv: Option<RustcVersion>,
 108 ) {
 109     if let hir::ExprKind::MethodCall(_, [filter_expr], _) = &target_expr.kind
 110         && let Some(copied_def_id) = cx.typeck_results().type_dependent_def_id(target_expr.hir_id)
 111         && (match_def_path(cx, copied_def_id, &paths::CORE_ITER_COPIED)
 112             || match_def_path(cx, copied_def_id, &paths::CORE_ITER_CLONED))
 113         && let hir::ExprKind::MethodCall(_, [iter_expr, _], _) = &filter_expr.kind
 114         && let Some(filter_def_id) = cx.typeck_results().type_dependent_def_id(filter_expr.hir_id)
 115         && match_def_path(cx, filter_def_id, &paths::CORE_ITER_FILTER)
 116         && let hir::ExprKind::MethodCall(_, [struct_expr], _) = &iter_expr.kind
 117         && let Some(iter_expr_def_id) = cx.typeck_results().type_dependent_def_id(iter_expr.hir_id)
 118         && match_acceptable_def_path(cx, iter_expr_def_id)
 119         && match_acceptable_type(cx, left_expr, msrv)
 120         && SpanlessEq::new(cx).eq_expr(left_expr, struct_expr) {
 121         suggest(cx, parent_expr, left_expr, filter_expr);
 122     }
 123 }
 124
 125 fn check_to_owned(
 126     cx: &LateContext<'_>,
 127     parent_expr: &hir::Expr<'_>,
 128     left_expr: &hir::Expr<'_>,
 129     target_expr: &hir::Expr<'_>,
 130     msrv: Option<RustcVersion>,
 131 ) {
 132     if meets_msrv(msrv,  msrvs::STRING_RETAIN)
 133         && let hir::ExprKind::MethodCall(_, [filter_expr], _) = &target_expr.kind
 134         && let Some(to_owned_def_id) = cx.typeck_results().type_dependent_def_id(target_expr.hir_id)
 135         && match_def_path(cx, to_owned_def_id, &paths::TO_OWNED_METHOD)
 136         && let hir::ExprKind::MethodCall(_, [chars_expr, _], _) = &filter_expr.kind
 137         && let Some(filter_def_id) = cx.typeck_results().type_dependent_def_id(filter_expr.hir_id)
 138         && match_def_path(cx, filter_def_id, &paths::CORE_ITER_FILTER)
 139         && let hir::ExprKind::MethodCall(_, [str_expr], _) = &chars_expr.kind
 140         && let Some(chars_expr_def_id) = cx.typeck_results().type_dependent_def_id(chars_expr.hir_id)
 141         && match_def_path(cx, chars_expr_def_id, &paths::STR_CHARS)
 142         && let ty = cx.typeck_results().expr_ty(str_expr).peel_refs()
 143         && is_type_diagnostic_item(cx, ty, sym::String)
 144         && SpanlessEq::new(cx).eq_expr(left_expr, str_expr) {
 145         suggest(cx, parent_expr, left_expr, filter_expr);
 146     }
 147 }
 148
 149 fn suggest(cx: &LateContext<'_>, parent_expr: &hir::Expr<'_>, left_expr: &hir::Expr<'_>, filter_expr: &hir::Expr<'_>) {
 150     if let hir::ExprKind::MethodCall(_, [_, closure], _) = filter_expr.kind
 151         && let hir::ExprKind::Closure(&hir::Closure { body, ..}) = closure.kind
 152         && let filter_body = cx.tcx.hir().body(body)
 153         && let [filter_params] = filter_body.params
 154         && let Some(sugg) = match filter_params.pat.kind {
 155             hir::PatKind::Binding(_, _, filter_param_ident, None) => {
 156                 Some(format!("{}.retain(|{}| {})", snippet(cx, left_expr.span, ".."), filter_param_ident, snippet(cx, filter_body.value.span, "..")))
 157             },
 158             hir::PatKind::Tuple([key_pat, value_pat], _) => {
 159                 make_sugg(cx, key_pat, value_pat, left_expr, filter_body)
 160             },
 161             hir::PatKind::Ref(pat, _) => {
 162                 match pat.kind {
 163                     hir::PatKind::Binding(_, _, filter_param_ident, None) => {
 164                         Some(format!("{}.retain(|{}| {})", snippet(cx, left_expr.span, ".."), filter_param_ident, snippet(cx, filter_body.value.span, "..")))
 165                     },
 166                     _ => None
 167                 }
 168             },
 169             _ => None
 170         } {
 171         span_lint_and_sugg(
 172             cx,
 173             MANUAL_RETAIN,
 174             parent_expr.span,
 175             "this expression can be written more simply using `.retain()`",
 176             "consider calling `.retain()` instead",
 177             sugg,
 178             Applicability::MachineApplicable
 179         );
 180     }
 181 }
 182
 183 fn make_sugg(
 184     cx: &LateContext<'_>,
 185     key_pat: &rustc_hir::Pat<'_>,
 186     value_pat: &rustc_hir::Pat<'_>,
 187     left_expr: &hir::Expr<'_>,
 188     filter_body: &hir::Body<'_>,
 189 ) -> Option<String> {
 190     match (&key_pat.kind, &value_pat.kind) {
 191         (hir::PatKind::Binding(_, _, key_param_ident, None), hir::PatKind::Binding(_, _, value_param_ident, None)) => {
 192             Some(format!(
 193                 "{}.retain(|{}, &mut {}| {})",
 194                 snippet(cx, left_expr.span, ".."),
 195                 key_param_ident,
 196                 value_param_ident,
 197                 snippet(cx, filter_body.value.span, "..")
 198             ))
 199         },
 200         (hir::PatKind::Binding(_, _, key_param_ident, None), hir::PatKind::Wild) => Some(format!(
 201             "{}.retain(|{}, _| {})",
 202             snippet(cx, left_expr.span, ".."),
 203             key_param_ident,
 204             snippet(cx, filter_body.value.span, "..")
 205         )),
 206         (hir::PatKind::Wild, hir::PatKind::Binding(_, _, value_param_ident, None)) => Some(format!(
 207             "{}.retain(|_, &mut {}| {})",
 208             snippet(cx, left_expr.span, ".."),
 209             value_param_ident,
 210             snippet(cx, filter_body.value.span, "..")
 211         )),
 212         _ => None,
 213     }
 214 }
 215
 216 fn match_acceptable_def_path(cx: &LateContext<'_>, collect_def_id: DefId) -> bool {
 217     ACCEPTABLE_METHODS
 218         .iter()
 219         .any(|&method| match_def_path(cx, collect_def_id, method))
 220 }
 221
 222 fn match_acceptable_type(cx: &LateContext<'_>, expr: &hir::Expr<'_>, msrv: Option<RustcVersion>) -> bool {
 223     let expr_ty = cx.typeck_results().expr_ty(expr).peel_refs();
 224     ACCEPTABLE_TYPES.iter().any(|(ty, acceptable_msrv)| {
 225         is_type_diagnostic_item(cx, expr_ty, *ty)
 226             && acceptable_msrv.map_or(true, |acceptable_msrv| meets_msrv(msrv, acceptable_msrv))
 227     })
 228 }