src/tools/clippy/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<'a, 'tcx>(
  56     cx: &'a LateContext<'a, 'tcx>,
  57     arg_id: hir::HirId,
  58     expr: &'tcx hir::Expr<'_>,
  59 ) -> (bool, bool) {
  60     match &expr.kind {
  61         hir::ExprKind::Call(ref func, ref args) => {
  62             if_chain! {
  63                 if let hir::ExprKind::Path(ref path) = func.kind;
  64                 then {
  65                     if match_qpath(path, &paths::OPTION_SOME) {
  66                         if_chain! {
  67                             if let hir::ExprKind::Path(path) = &args[0].kind;
  68                             if let Res::Local(ref local) = cx.tables().qpath_res(path, args[0].hir_id);
  69                             then {
  70                                 if arg_id == *local {
  71                                     return (false, false)
  72                                 }
  73                             }
  74                         }
  75                         return (true, false);
  76                     } else {
  77                         // We don't know. It might do anything.
  78                         return (true, true);
  79                     }
  80                 }
  81             }
  82             (true, true)
  83         },
  84         hir::ExprKind::Block(ref block, _) => {
  85             if let Some(expr) = &block.expr {
  86                 check_expression(cx, arg_id, &expr)
  87             } else {
  88                 (false, false)
  89             }
  90         },
  91         hir::ExprKind::Match(_, arms, _) => {
  92             let mut found_mapping = false;
  93             let mut found_filtering = false;
  94             for arm in *arms {
  95                 let (m, f) = check_expression(cx, arg_id, &arm.body);
  96                 found_mapping |= m;
  97                 found_filtering |= f;
  98             }
  99             (found_mapping, found_filtering)
 100         },
 101         hir::ExprKind::Path(path) if match_qpath(path, &paths::OPTION_NONE) => (false, true),
 102         _ => (true, true),
 103     }
 104 }
 105
 106 struct ReturnVisitor<'a, 'tcx> {
 107     cx: &'a LateContext<'a, 'tcx>,
 108     arg_id: hir::HirId,
 109     // Found a non-None return that isn't Some(input)
 110     found_mapping: bool,
 111     // Found a return that isn't Some
 112     found_filtering: bool,
 113 }
 114
 115 impl<'a, 'tcx> ReturnVisitor<'a, 'tcx> {
 116     fn new(cx: &'a LateContext<'a, 'tcx>, arg_id: hir::HirId) -> ReturnVisitor<'a, 'tcx> {
 117         ReturnVisitor {
 118             cx,
 119             arg_id,
 120             found_mapping: false,
 121             found_filtering: false,
 122         }
 123     }
 124 }
 125
 126 impl<'a, 'tcx> Visitor<'tcx> for ReturnVisitor<'a, 'tcx> {
 127     type Map = Map<'tcx>;
 128
 129     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
 130         if let hir::ExprKind::Ret(Some(expr)) = &expr.kind {
 131             let (found_mapping, found_filtering) = check_expression(self.cx, self.arg_id, expr);
 132             self.found_mapping |= found_mapping;
 133             self.found_filtering |= found_filtering;
 134         } else {
 135             walk_expr(self, expr);
 136         }
 137     }
 138
 139     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 140         NestedVisitorMap::None
 141     }
 142 }