src/tools/clippy/clippy_lints/src/manual_non_exhaustive.rs

   1 use clippy_utils::diagnostics::{span_lint_and_then, span_lint_hir_and_then};
   2 use clippy_utils::is_doc_hidden;
   3 use clippy_utils::msrvs::{self, Msrv};
   4 use clippy_utils::source::snippet_opt;
   5 use rustc_ast::ast::{self, VisibilityKind};
   6 use rustc_data_structures::fx::FxHashSet;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
   9 use rustc_hir::{self as hir, Expr, ExprKind, QPath};
  10 use rustc_lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  11 use rustc_middle::ty::DefIdTree;
  12 use rustc_session::{declare_tool_lint, impl_lint_pass};
  13 use rustc_span::def_id::{DefId, LocalDefId};
  14 use rustc_span::{sym, Span};
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Checks for manual implementations of the non-exhaustive pattern.
  19     ///
  20     /// ### Why is this bad?
  21     /// Using the #[non_exhaustive] attribute expresses better the intent
  22     /// and allows possible optimizations when applied to enums.
  23     ///
  24     /// ### Example
  25     /// ```rust
  26     /// struct S {
  27     ///     pub a: i32,
  28     ///     pub b: i32,
  29     ///     _c: (),
  30     /// }
  31     ///
  32     /// enum E {
  33     ///     A,
  34     ///     B,
  35     ///     #[doc(hidden)]
  36     ///     _C,
  37     /// }
  38     ///
  39     /// struct T(pub i32, pub i32, ());
  40     /// ```
  41     /// Use instead:
  42     /// ```rust
  43     /// #[non_exhaustive]
  44     /// struct S {
  45     ///     pub a: i32,
  46     ///     pub b: i32,
  47     /// }
  48     ///
  49     /// #[non_exhaustive]
  50     /// enum E {
  51     ///     A,
  52     ///     B,
  53     /// }
  54     ///
  55     /// #[non_exhaustive]
  56     /// struct T(pub i32, pub i32);
  57     /// ```
  58     #[clippy::version = "1.45.0"]
  59     pub MANUAL_NON_EXHAUSTIVE,
  60     style,
  61     "manual implementations of the non-exhaustive pattern can be simplified using #[non_exhaustive]"
  62 }
  63
  64 #[expect(clippy::module_name_repetitions)]
  65 pub struct ManualNonExhaustiveStruct {
  66     msrv: Msrv,
  67 }
  68
  69 impl ManualNonExhaustiveStruct {
  70     #[must_use]
  71     pub fn new(msrv: Msrv) -> Self {
  72         Self { msrv }
  73     }
  74 }
  75
  76 impl_lint_pass!(ManualNonExhaustiveStruct => [MANUAL_NON_EXHAUSTIVE]);
  77
  78 #[expect(clippy::module_name_repetitions)]
  79 pub struct ManualNonExhaustiveEnum {
  80     msrv: Msrv,
  81     constructed_enum_variants: FxHashSet<(DefId, DefId)>,
  82     potential_enums: Vec<(LocalDefId, LocalDefId, Span, Span)>,
  83 }
  84
  85 impl ManualNonExhaustiveEnum {
  86     #[must_use]
  87     pub fn new(msrv: Msrv) -> Self {
  88         Self {
  89             msrv,
  90             constructed_enum_variants: FxHashSet::default(),
  91             potential_enums: Vec::new(),
  92         }
  93     }
  94 }
  95
  96 impl_lint_pass!(ManualNonExhaustiveEnum => [MANUAL_NON_EXHAUSTIVE]);
  97
  98 impl EarlyLintPass for ManualNonExhaustiveStruct {
  99     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
 100         if !self.msrv.meets(msrvs::NON_EXHAUSTIVE) {
 101             return;
 102         }
 103
 104         if let ast::ItemKind::Struct(variant_data, _) = &item.kind {
 105             let (fields, delimiter) = match variant_data {
 106                 ast::VariantData::Struct(fields, _) => (&**fields, '{'),
 107                 ast::VariantData::Tuple(fields, _) => (&**fields, '('),
 108                 ast::VariantData::Unit(_) => return,
 109             };
 110             if fields.len() <= 1 {
 111                 return;
 112             }
 113             let mut iter = fields.iter().filter_map(|f| match f.vis.kind {
 114                 VisibilityKind::Public => None,
 115                 VisibilityKind::Inherited => Some(Ok(f)),
 116                 VisibilityKind::Restricted { .. } => Some(Err(())),
 117             });
 118             if let Some(Ok(field)) = iter.next()
 119                 && iter.next().is_none()
 120                 && field.ty.kind.is_unit()
 121                 && field.ident.map_or(true, |name| name.as_str().starts_with('_'))
 122             {
 123                 span_lint_and_then(
 124                     cx,
 125                     MANUAL_NON_EXHAUSTIVE,
 126                     item.span,
 127                     "this seems like a manual implementation of the non-exhaustive pattern",
 128                     |diag| {
 129                         if !item.attrs.iter().any(|attr| attr.has_name(sym::non_exhaustive))
 130                             && let header_span = cx.sess().source_map().span_until_char(item.span, delimiter)
 131                             && let Some(snippet) = snippet_opt(cx, header_span)
 132                         {
 133                             diag.span_suggestion(
 134                                 header_span,
 135                                 "add the attribute",
 136                                 format!("#[non_exhaustive] {snippet}"),
 137                                 Applicability::Unspecified,
 138                             );
 139                         }
 140                         diag.span_help(field.span, "remove this field");
 141                     }
 142                 );
 143             }
 144         }
 145     }
 146
 147     extract_msrv_attr!(EarlyContext);
 148 }
 149
 150 impl<'tcx> LateLintPass<'tcx> for ManualNonExhaustiveEnum {
 151     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
 152         if !self.msrv.meets(msrvs::NON_EXHAUSTIVE) {
 153             return;
 154         }
 155
 156         if let hir::ItemKind::Enum(def, _) = &item.kind
 157             && def.variants.len() > 1
 158         {
 159             let mut iter = def.variants.iter().filter_map(|v| {
 160                 let id = cx.tcx.hir().local_def_id(v.hir_id);
 161                 (matches!(v.data, hir::VariantData::Unit(..))
 162                     && v.ident.as_str().starts_with('_')
 163                     && is_doc_hidden(cx.tcx.hir().attrs(v.hir_id)))
 164                 .then_some((id, v.span))
 165             });
 166             if let Some((id, span)) = iter.next()
 167                 && iter.next().is_none()
 168             {
 169                 self.potential_enums.push((item.owner_id.def_id, id, item.span, span));
 170             }
 171         }
 172     }
 173
 174     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 175         if let ExprKind::Path(QPath::Resolved(None, p)) = &e.kind
 176             && let [.., name] = p.segments
 177             && let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Const), id) = p.res
 178             && name.ident.as_str().starts_with('_')
 179         {
 180             let variant_id = cx.tcx.parent(id);
 181             let enum_id = cx.tcx.parent(variant_id);
 182
 183             self.constructed_enum_variants.insert((enum_id, variant_id));
 184         }
 185     }
 186
 187     fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
 188         for &(enum_id, _, enum_span, variant_span) in
 189             self.potential_enums.iter().filter(|&&(enum_id, variant_id, _, _)| {
 190                 !self
 191                     .constructed_enum_variants
 192                     .contains(&(enum_id.to_def_id(), variant_id.to_def_id()))
 193             })
 194         {
 195             let hir_id = cx.tcx.hir().local_def_id_to_hir_id(enum_id);
 196             span_lint_hir_and_then(
 197                 cx,
 198                 MANUAL_NON_EXHAUSTIVE,
 199                 hir_id,
 200                 enum_span,
 201                 "this seems like a manual implementation of the non-exhaustive pattern",
 202                 |diag| {
 203                     if !cx.tcx.adt_def(enum_id).is_variant_list_non_exhaustive()
 204                         && let header_span = cx.sess().source_map().span_until_char(enum_span, '{')
 205                         && let Some(snippet) = snippet_opt(cx, header_span)
 206                     {
 207                             diag.span_suggestion(
 208                                 header_span,
 209                                 "add the attribute",
 210                                 format!("#[non_exhaustive] {snippet}"),
 211                                 Applicability::Unspecified,
 212                             );
 213                     }
 214                     diag.span_help(variant_span, "remove this variant");
 215                 },
 216             );
 217         }
 218     }
 219
 220     extract_msrv_attr!(LateContext);
 221 }