clippy_lints/src/methods/unnecessary_filter_map.rs

   1 use crate::utils::paths;
   2 use crate::utils::usage::mutated_variables;
   3 use crate::utils::{match_qpath, match_trait_method, span_lint};
   4 use rustc_hir as hir;
   5 use rustc_hir::def::Res;
   6 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::hir::map::Map;
   9
  10 use if_chain::if_chain;
  11
  12 use super::UNNECESSARY_FILTER_MAP;
  13
  14 pub(super) fn lint(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
  15     if !match_trait_method(cx, expr, &paths::ITERATOR) {
  16         return;
  17     }
  18
  19     if let hir::ExprKind::Closure(_, _, body_id, ..) = args[1].kind {
  20         let body = cx.tcx.hir().body(body_id);
  21         let arg_id = body.params[0].pat.hir_id;
  22         let mutates_arg =
  23             mutated_variables(&body.value, cx).map_or(true, |used_mutably| used_mutably.contains(&arg_id));
  24
  25         let (mut found_mapping, mut found_filtering) = check_expression(&cx, arg_id, &body.value);
  26
  27         let mut return_visitor = ReturnVisitor::new(&cx, arg_id);
  28         return_visitor.visit_expr(&body.value);
  29         found_mapping |= return_visitor.found_mapping;
  30         found_filtering |= return_visitor.found_filtering;
  31
  32         if !found_filtering {
  33             span_lint(
  34                 cx,
  35                 UNNECESSARY_FILTER_MAP,
  36                 expr.span,
  37                 "this `.filter_map` can be written more simply using `.map`",
  38             );
  39             return;
  40         }
  41
  42         if !found_mapping && !mutates_arg {
  43             span_lint(
  44                 cx,
  45                 UNNECESSARY_FILTER_MAP,
  46                 expr.span,
  47                 "this `.filter_map` can be written more simply using `.filter`",
  48             );
  49             return;
  50         }
  51     }
  52 }
  53
  54 // returns (found_mapping, found_filtering)
  55 fn check_expression<'tcx>(cx: &LateContext<'tcx>, arg_id: hir::HirId, expr: &'tcx hir::Expr<'_>) -> (bool, bool) {
  56     match &expr.kind {
  57         hir::ExprKind::Call(ref func, ref args) => {
  58             if_chain! {
  59                 if let hir::ExprKind::Path(ref path) = func.kind;
  60                 then {
  61                     if match_qpath(path, &paths::OPTION_SOME) {
  62                         if_chain! {
  63                             if let hir::ExprKind::Path(path) = &args[0].kind;
  64                             if let Res::Local(ref local) = cx.qpath_res(path, args[0].hir_id);
  65                             then {
  66                                 if arg_id == *local {
  67                                     return (false, false)
  68                                 }
  69                             }
  70                         }
  71                         return (true, false);
  72                     } else {
  73                         // We don't know. It might do anything.
  74                         return (true, true);
  75                     }
  76                 }
  77             }
  78             (true, true)
  79         },
  80         hir::ExprKind::Block(ref block, _) => {
  81             if let Some(expr) = &block.expr {
  82                 check_expression(cx, arg_id, &expr)
  83             } else {
  84                 (false, false)
  85             }
  86         },
  87         hir::ExprKind::Match(_, arms, _) => {
  88             let mut found_mapping = false;
  89             let mut found_filtering = false;
  90             for arm in *arms {
  91                 let (m, f) = check_expression(cx, arg_id, &arm.body);
  92                 found_mapping |= m;
  93                 found_filtering |= f;
  94             }
  95             (found_mapping, found_filtering)
  96         },
  97         hir::ExprKind::Path(path) if match_qpath(path, &paths::OPTION_NONE) => (false, true),
  98         _ => (true, true),
  99     }
 100 }
 101
 102 struct ReturnVisitor<'a, 'tcx> {
 103     cx: &'a LateContext<'tcx>,
 104     arg_id: hir::HirId,
 105     // Found a non-None return that isn't Some(input)
 106     found_mapping: bool,
 107     // Found a return that isn't Some
 108     found_filtering: bool,
 109 }
 110
 111 impl<'a, 'tcx> ReturnVisitor<'a, 'tcx> {
 112     fn new(cx: &'a LateContext<'tcx>, arg_id: hir::HirId) -> ReturnVisitor<'a, 'tcx> {
 113         ReturnVisitor {
 114             cx,
 115             arg_id,
 116             found_mapping: false,
 117             found_filtering: false,
 118         }
 119     }
 120 }
 121
 122 impl<'a, 'tcx> Visitor<'tcx> for ReturnVisitor<'a, 'tcx> {
 123     type Map = Map<'tcx>;
 124
 125     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
 126         if let hir::ExprKind::Ret(Some(expr)) = &expr.kind {
 127             let (found_mapping, found_filtering) = check_expression(self.cx, self.arg_id, expr);
 128             self.found_mapping |= found_mapping;
 129             self.found_filtering |= found_filtering;
 130         } else {
 131             walk_expr(self, expr);
 132         }
 133     }
 134
 135     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 136         NestedVisitorMap::None
 137     }
 138 }