clippy_lints/src/inherent_impl.rs

   1 //! lint on inherent implementations
   2
   3 use crate::rustc::hir::*;
   4 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use crate::rustc::{declare_tool_lint, lint_array};
   6 use crate::rustc_data_structures::fx::FxHashMap;
   7 use std::default::Default;
   8 use crate::syntax_pos::Span;
   9 use crate::utils::span_lint_and_then;
  10
  11 /// **What it does:** Checks for multiple inherent implementations of a struct
  12 ///
  13 /// **Why is this bad?** Splitting the implementation of a type makes the code harder to navigate.
  14 ///
  15 /// **Known problems:** None.
  16 ///
  17 /// **Example:**
  18 /// ```rust
  19 /// struct X;
  20 /// impl X {
  21 ///     fn one() {}
  22 /// }
  23 /// impl X {
  24 ///     fn other() {}
  25 /// }
  26 /// ```
  27 ///
  28 /// Could be written:
  29 ///
  30 /// ```rust
  31 /// struct X;
  32 /// impl X {
  33 ///     fn one() {}
  34 ///     fn other() {}
  35 /// }
  36 /// ```
  37 declare_clippy_lint! {
  38     pub MULTIPLE_INHERENT_IMPL,
  39     restriction,
  40     "Multiple inherent impl that could be grouped"
  41 }
  42
  43 pub struct Pass {
  44     impls: FxHashMap<def_id::DefId, (Span, Generics)>,
  45 }
  46
  47 impl Default for Pass {
  48     fn default() -> Self {
  49         Self { impls: FxHashMap::default() }
  50     }
  51 }
  52
  53 impl LintPass for Pass {
  54     fn get_lints(&self) -> LintArray {
  55         lint_array!(MULTIPLE_INHERENT_IMPL)
  56     }
  57 }
  58
  59 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  60     fn check_item(&mut self, _: &LateContext<'a, 'tcx>, item: &'tcx Item) {
  61         if let ItemKind::Impl(_, _, _, ref generics, None, _, _) = item.node {
  62             // Remember for each inherent implementation encoutered its span and generics
  63             self.impls
  64                 .insert(item.hir_id.owner_def_id(), (item.span, generics.clone()));
  65         }
  66     }
  67
  68     fn check_crate_post(&mut self, cx: &LateContext<'a, 'tcx>, krate: &'tcx Crate) {
  69         if let Some(item) = krate.items.values().nth(0) {
  70             // Retrieve all inherent implementations from the crate, grouped by type
  71             for impls in cx
  72                 .tcx
  73                 .crate_inherent_impls(item.hir_id.owner_def_id().krate)
  74                 .inherent_impls
  75                 .values()
  76             {
  77                 // Filter out implementations that have generic params (type or lifetime)
  78                 let mut impl_spans = impls
  79                     .iter()
  80                     .filter_map(|impl_def| self.impls.get(impl_def))
  81                     .filter_map(|(span, generics)| if generics.params.len() == 0 {
  82                         Some(span)
  83                     } else {
  84                         None
  85                     });
  86                 if let Some(initial_span) = impl_spans.nth(0) {
  87                     impl_spans.for_each(|additional_span| {
  88                         span_lint_and_then(
  89                             cx,
  90                             MULTIPLE_INHERENT_IMPL,
  91                             *additional_span,
  92                             "Multiple implementations of this structure",
  93                             |db| {
  94                                 db.span_note(
  95                                     *initial_span,
  96                                     "First implementation here",
  97                                 );
  98                             },
  99                         )
 100                     })
 101                 }
 102             }
 103         }
 104     }
 105 }