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[rustc.git] / src / tools / clippy / clippy_lints / src / inherent_impl.rs
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1//! lint on inherent implementations
2
17df50a5 3use clippy_utils::diagnostics::span_lint_and_note;
a2a8927a 4use clippy_utils::is_lint_allowed;
17df50a5 5use rustc_data_structures::fx::FxHashMap;
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6use rustc_hir::def_id::LocalDefId;
7use rustc_hir::{Item, ItemKind, Node};
f20569fa 8use rustc_lint::{LateContext, LateLintPass};
4b012472 9use rustc_session::declare_lint_pass;
f20569fa 10use rustc_span::Span;
17df50a5 11use std::collections::hash_map::Entry;
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12
13declare_clippy_lint! {
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14 /// ### What it does
15 /// Checks for multiple inherent implementations of a struct
f20569fa 16 ///
31ef2f64 17 /// ### Why restrict this?
94222f64 18 /// Splitting the implementation of a type makes the code harder to navigate.
f20569fa 19 ///
94222f64 20 /// ### Example
ed00b5ec 21 /// ```no_run
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22 /// struct X;
23 /// impl X {
24 /// fn one() {}
25 /// }
26 /// impl X {
27 /// fn other() {}
28 /// }
29 /// ```
30 ///
31 /// Could be written:
32 ///
ed00b5ec 33 /// ```no_run
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34 /// struct X;
35 /// impl X {
36 /// fn one() {}
37 /// fn other() {}
38 /// }
39 /// ```
a2a8927a 40 #[clippy::version = "pre 1.29.0"]
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41 pub MULTIPLE_INHERENT_IMPL,
42 restriction,
43 "Multiple inherent impl that could be grouped"
44}
45
17df50a5 46declare_lint_pass!(MultipleInherentImpl => [MULTIPLE_INHERENT_IMPL]);
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47
48impl<'tcx> LateLintPass<'tcx> for MultipleInherentImpl {
c295e0f8 49 fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
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50 // Map from a type to it's first impl block. Needed to distinguish generic arguments.
51 // e.g. `Foo<Bar>` and `Foo<Baz>`
52 let mut type_map = FxHashMap::default();
53 // List of spans to lint. (lint_span, first_span)
54 let mut lint_spans = Vec::new();
55
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56 let Ok(impls) = cx.tcx.crate_inherent_impls(()) else {
57 return;
58 };
9c376795 59 let inherent_impls = cx
17df50a5 60 .tcx
c0240ec0 61 .with_stable_hashing_context(|hcx| impls.inherent_impls.to_sorted(&hcx, true));
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62
63 for (_, impl_ids) in inherent_impls.into_iter().filter(|(&id, impls)| {
64 impls.len() > 1
65 // Check for `#[allow]` on the type definition
66 && !is_lint_allowed(
67 cx,
68 MULTIPLE_INHERENT_IMPL,
4b012472 69 cx.tcx.local_def_id_to_hir_id(id),
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70 )
71 }) {
17df50a5 72 for impl_id in impl_ids.iter().map(|id| id.expect_local()) {
add651ee 73 let impl_ty = cx.tcx.type_of(impl_id).instantiate_identity();
9ffffee4 74 match type_map.entry(impl_ty) {
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75 Entry::Vacant(e) => {
76 // Store the id for the first impl block of this type. The span is retrieved lazily.
77 e.insert(IdOrSpan::Id(impl_id));
78 },
79 Entry::Occupied(mut e) => {
80 if let Some(span) = get_impl_span(cx, impl_id) {
81 let first_span = match *e.get() {
82 IdOrSpan::Span(s) => s,
83 IdOrSpan::Id(id) => {
84 if let Some(s) = get_impl_span(cx, id) {
85 // Remember the span of the first block.
86 *e.get_mut() = IdOrSpan::Span(s);
87 s
88 } else {
89 // The first impl block isn't considered by the lint. Replace it with the
90 // current one.
91 *e.get_mut() = IdOrSpan::Span(span);
92 continue;
93 }
94 },
95 };
96 lint_spans.push((span, first_span));
97 }
98 },
99 }
f20569fa 100 }
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101
102 // Switching to the next type definition, no need to keep the current entries around.
103 type_map.clear();
f20569fa 104 }
f20569fa 105
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106 // `TyCtxt::crate_inherent_impls` doesn't have a defined order. Sort the lint output first.
107 lint_spans.sort_by_key(|x| x.0.lo());
108 for (span, first_span) in lint_spans {
109 span_lint_and_note(
110 cx,
111 MULTIPLE_INHERENT_IMPL,
112 span,
113 "multiple implementations of this structure",
114 Some(first_span),
115 "first implementation here",
116 );
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117 }
118 }
119}
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120
121/// Gets the span for the given impl block unless it's not being considered by the lint.
122fn get_impl_span(cx: &LateContext<'_>, id: LocalDefId) -> Option<Span> {
4b012472 123 let id = cx.tcx.local_def_id_to_hir_id(id);
17df50a5 124 if let Node::Item(&Item {
04454e1e 125 kind: ItemKind::Impl(impl_item),
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126 span,
127 ..
4b012472 128 }) = cx.tcx.hir_node(id)
17df50a5 129 {
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130 (!span.from_expansion()
131 && impl_item.generics.params.is_empty()
132 && !is_lint_allowed(cx, MULTIPLE_INHERENT_IMPL, id))
064997fb 133 .then_some(span)
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134 } else {
135 None
136 }
137}
138
139enum IdOrSpan {
140 Id(LocalDefId),
141 Span(Span),
142}