clippy_lints/src/manual_non_exhaustive.rs

   1 use clippy_utils::attrs::is_doc_hidden;
   2 use clippy_utils::diagnostics::span_lint_and_then;
   3 use clippy_utils::source::snippet_opt;
   4 use clippy_utils::{meets_msrv, msrvs};
   5 use if_chain::if_chain;
   6 use rustc_ast::ast::{FieldDef, Item, ItemKind, Variant, VariantData, VisibilityKind};
   7 use rustc_errors::Applicability;
   8 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
   9 use rustc_semver::RustcVersion;
  10 use rustc_session::{declare_tool_lint, impl_lint_pass};
  11 use rustc_span::{sym, Span};
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for manual implementations of the non-exhaustive pattern.
  16     ///
  17     /// ### Why is this bad?
  18     /// Using the #[non_exhaustive] attribute expresses better the intent
  19     /// and allows possible optimizations when applied to enums.
  20     ///
  21     /// ### Example
  22     /// ```rust
  23     /// struct S {
  24     ///     pub a: i32,
  25     ///     pub b: i32,
  26     ///     _c: (),
  27     /// }
  28     ///
  29     /// enum E {
  30     ///     A,
  31     ///     B,
  32     ///     #[doc(hidden)]
  33     ///     _C,
  34     /// }
  35     ///
  36     /// struct T(pub i32, pub i32, ());
  37     /// ```
  38     /// Use instead:
  39     /// ```rust
  40     /// #[non_exhaustive]
  41     /// struct S {
  42     ///     pub a: i32,
  43     ///     pub b: i32,
  44     /// }
  45     ///
  46     /// #[non_exhaustive]
  47     /// enum E {
  48     ///     A,
  49     ///     B,
  50     /// }
  51     ///
  52     /// #[non_exhaustive]
  53     /// struct T(pub i32, pub i32);
  54     /// ```
  55     #[clippy::version = "1.45.0"]
  56     pub MANUAL_NON_EXHAUSTIVE,
  57     style,
  58     "manual implementations of the non-exhaustive pattern can be simplified using #[non_exhaustive]"
  59 }
  60
  61 #[derive(Clone)]
  62 pub struct ManualNonExhaustive {
  63     msrv: Option<RustcVersion>,
  64 }
  65
  66 impl ManualNonExhaustive {
  67     #[must_use]
  68     pub fn new(msrv: Option<RustcVersion>) -> Self {
  69         Self { msrv }
  70     }
  71 }
  72
  73 impl_lint_pass!(ManualNonExhaustive => [MANUAL_NON_EXHAUSTIVE]);
  74
  75 impl EarlyLintPass for ManualNonExhaustive {
  76     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  77         if !meets_msrv(self.msrv.as_ref(), &msrvs::NON_EXHAUSTIVE) {
  78             return;
  79         }
  80
  81         match &item.kind {
  82             ItemKind::Enum(def, _) => {
  83                 check_manual_non_exhaustive_enum(cx, item, &def.variants);
  84             },
  85             ItemKind::Struct(variant_data, _) => {
  86                 if let VariantData::Unit(..) = variant_data {
  87                     return;
  88                 }
  89
  90                 check_manual_non_exhaustive_struct(cx, item, variant_data);
  91             },
  92             _ => {},
  93         }
  94     }
  95
  96     extract_msrv_attr!(EarlyContext);
  97 }
  98
  99 fn check_manual_non_exhaustive_enum(cx: &EarlyContext<'_>, item: &Item, variants: &[Variant]) {
 100     fn is_non_exhaustive_marker(variant: &Variant) -> bool {
 101         matches!(variant.data, VariantData::Unit(_))
 102             && variant.ident.as_str().starts_with('_')
 103             && is_doc_hidden(&variant.attrs)
 104     }
 105
 106     let mut markers = variants.iter().filter(|v| is_non_exhaustive_marker(v));
 107     if_chain! {
 108         if let Some(marker) = markers.next();
 109         if markers.count() == 0 && variants.len() > 1;
 110         then {
 111             span_lint_and_then(
 112                 cx,
 113                 MANUAL_NON_EXHAUSTIVE,
 114                 item.span,
 115                 "this seems like a manual implementation of the non-exhaustive pattern",
 116                 |diag| {
 117                     if_chain! {
 118                         if !item.attrs.iter().any(|attr| attr.has_name(sym::non_exhaustive));
 119                         let header_span = cx.sess().source_map().span_until_char(item.span, '{');
 120                         if let Some(snippet) = snippet_opt(cx, header_span);
 121                         then {
 122                             diag.span_suggestion(
 123                                 header_span,
 124                                 "add the attribute",
 125                                 format!("#[non_exhaustive] {}", snippet),
 126                                 Applicability::Unspecified,
 127                             );
 128                         }
 129                     }
 130                     diag.span_help(marker.span, "remove this variant");
 131                 });
 132         }
 133     }
 134 }
 135
 136 fn check_manual_non_exhaustive_struct(cx: &EarlyContext<'_>, item: &Item, data: &VariantData) {
 137     fn is_private(field: &FieldDef) -> bool {
 138         matches!(field.vis.kind, VisibilityKind::Inherited)
 139     }
 140
 141     fn is_non_exhaustive_marker(field: &FieldDef) -> bool {
 142         is_private(field) && field.ty.kind.is_unit() && field.ident.map_or(true, |n| n.as_str().starts_with('_'))
 143     }
 144
 145     fn find_header_span(cx: &EarlyContext<'_>, item: &Item, data: &VariantData) -> Span {
 146         let delimiter = match data {
 147             VariantData::Struct(..) => '{',
 148             VariantData::Tuple(..) => '(',
 149             VariantData::Unit(_) => unreachable!("`VariantData::Unit` is already handled above"),
 150         };
 151
 152         cx.sess().source_map().span_until_char(item.span, delimiter)
 153     }
 154
 155     let fields = data.fields();
 156     let private_fields = fields.iter().filter(|f| is_private(f)).count();
 157     let public_fields = fields.iter().filter(|f| f.vis.kind.is_pub()).count();
 158
 159     if_chain! {
 160         if private_fields == 1 && public_fields >= 1 && public_fields == fields.len() - 1;
 161         if let Some(marker) = fields.iter().find(|f| is_non_exhaustive_marker(f));
 162         then {
 163             span_lint_and_then(
 164                 cx,
 165                 MANUAL_NON_EXHAUSTIVE,
 166                 item.span,
 167                 "this seems like a manual implementation of the non-exhaustive pattern",
 168                 |diag| {
 169                     if_chain! {
 170                         if !item.attrs.iter().any(|attr| attr.has_name(sym::non_exhaustive));
 171                         let header_span = find_header_span(cx, item, data);
 172                         if let Some(snippet) = snippet_opt(cx, header_span);
 173                         then {
 174                             diag.span_suggestion(
 175                                 header_span,
 176                                 "add the attribute",
 177                                 format!("#[non_exhaustive] {}", snippet),
 178                                 Applicability::Unspecified,
 179                             );
 180                         }
 181                     }
 182                     diag.span_help(marker.span, "remove this field");
 183                 });
 184         }
 185     }
 186 }