src/tools/clippy/clippy_lints/src/methods/unnecessary_filter_map.rs

   1 use crate::utils::usage::mutated_variables;
   2 use crate::utils::{match_qpath, match_trait_method, path_to_local_id, paths, span_lint};
   3 use rustc_hir as hir;
   4 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   5 use rustc_lint::LateContext;
   6 use rustc_middle::hir::map::Map;
   7
   8 use if_chain::if_chain;
   9
  10 use super::UNNECESSARY_FILTER_MAP;
  11
  12 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
  13     if !match_trait_method(cx, expr, &paths::ITERATOR) {
  14         return;
  15     }
  16
  17     if let hir::ExprKind::Closure(_, _, body_id, ..) = args[1].kind {
  18         let body = cx.tcx.hir().body(body_id);
  19         let arg_id = body.params[0].pat.hir_id;
  20         let mutates_arg =
  21             mutated_variables(&body.value, cx).map_or(true, |used_mutably| used_mutably.contains(&arg_id));
  22
  23         let (mut found_mapping, mut found_filtering) = check_expression(&cx, arg_id, &body.value);
  24
  25         let mut return_visitor = ReturnVisitor::new(&cx, arg_id);
  26         return_visitor.visit_expr(&body.value);
  27         found_mapping |= return_visitor.found_mapping;
  28         found_filtering |= return_visitor.found_filtering;
  29
  30         if !found_filtering {
  31             span_lint(
  32                 cx,
  33                 UNNECESSARY_FILTER_MAP,
  34                 expr.span,
  35                 "this `.filter_map` can be written more simply using `.map`",
  36             );
  37             return;
  38         }
  39
  40         if !found_mapping && !mutates_arg {
  41             span_lint(
  42                 cx,
  43                 UNNECESSARY_FILTER_MAP,
  44                 expr.span,
  45                 "this `.filter_map` can be written more simply using `.filter`",
  46             );
  47             return;
  48         }
  49     }
  50 }
  51
  52 // returns (found_mapping, found_filtering)
  53 fn check_expression<'tcx>(cx: &LateContext<'tcx>, arg_id: hir::HirId, expr: &'tcx hir::Expr<'_>) -> (bool, bool) {
  54     match &expr.kind {
  55         hir::ExprKind::Call(ref func, ref args) => {
  56             if_chain! {
  57                 if let hir::ExprKind::Path(ref path) = func.kind;
  58                 then {
  59                     if match_qpath(path, &paths::OPTION_SOME) {
  60                         if path_to_local_id(&args[0], arg_id) {
  61                             return (false, false)
  62                         }
  63                         return (true, false);
  64                     }
  65                     // We don't know. It might do anything.
  66                     return (true, true);
  67                 }
  68             }
  69             (true, true)
  70         },
  71         hir::ExprKind::Block(ref block, _) => block
  72             .expr
  73             .as_ref()
  74             .map_or((false, false), |expr| check_expression(cx, arg_id, &expr)),
  75         hir::ExprKind::Match(_, arms, _) => {
  76             let mut found_mapping = false;
  77             let mut found_filtering = false;
  78             for arm in *arms {
  79                 let (m, f) = check_expression(cx, arg_id, &arm.body);
  80                 found_mapping |= m;
  81                 found_filtering |= f;
  82             }
  83             (found_mapping, found_filtering)
  84         },
  85         // There must be an else_arm or there will be a type error
  86         hir::ExprKind::If(_, ref if_arm, Some(ref else_arm)) => {
  87             let if_check = check_expression(cx, arg_id, if_arm);
  88             let else_check = check_expression(cx, arg_id, else_arm);
  89             (if_check.0 | else_check.0, if_check.1 | else_check.1)
  90         },
  91         hir::ExprKind::Path(path) if match_qpath(path, &paths::OPTION_NONE) => (false, true),
  92         _ => (true, true),
  93     }
  94 }
  95
  96 struct ReturnVisitor<'a, 'tcx> {
  97     cx: &'a LateContext<'tcx>,
  98     arg_id: hir::HirId,
  99     // Found a non-None return that isn't Some(input)
 100     found_mapping: bool,
 101     // Found a return that isn't Some
 102     found_filtering: bool,
 103 }
 104
 105 impl<'a, 'tcx> ReturnVisitor<'a, 'tcx> {
 106     fn new(cx: &'a LateContext<'tcx>, arg_id: hir::HirId) -> ReturnVisitor<'a, 'tcx> {
 107         ReturnVisitor {
 108             cx,
 109             arg_id,
 110             found_mapping: false,
 111             found_filtering: false,
 112         }
 113     }
 114 }
 115
 116 impl<'a, 'tcx> Visitor<'tcx> for ReturnVisitor<'a, 'tcx> {
 117     type Map = Map<'tcx>;
 118
 119     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
 120         if let hir::ExprKind::Ret(Some(expr)) = &expr.kind {
 121             let (found_mapping, found_filtering) = check_expression(self.cx, self.arg_id, expr);
 122             self.found_mapping |= found_mapping;
 123             self.found_filtering |= found_filtering;
 124         } else {
 125             walk_expr(self, expr);
 126         }
 127     }
 128
 129     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 130         NestedVisitorMap::None
 131     }
 132 }