src/tools/clippy/clippy_lints/src/excessive_bools.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::{get_parent_as_impl, has_repr_attr, is_bool};
   3 use rustc_hir::intravisit::FnKind;
   4 use rustc_hir::{Body, FnDecl, Item, ItemKind, TraitFn, TraitItem, TraitItemKind, Ty};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_tool_lint, impl_lint_pass};
   7 use rustc_span::def_id::LocalDefId;
   8 use rustc_span::Span;
   9 use rustc_target::spec::abi::Abi;
  10
  11 declare_clippy_lint! {
  12     /// ### What it does
  13     /// Checks for excessive
  14     /// use of bools in structs.
  15     ///
  16     /// ### Why is this bad?
  17     /// Excessive bools in a struct
  18     /// is often a sign that it's used as a state machine,
  19     /// which is much better implemented as an enum.
  20     /// If it's not the case, excessive bools usually benefit
  21     /// from refactoring into two-variant enums for better
  22     /// readability and API.
  23     ///
  24     /// ### Example
  25     /// ```no_run
  26     /// struct S {
  27     ///     is_pending: bool,
  28     ///     is_processing: bool,
  29     ///     is_finished: bool,
  30     /// }
  31     /// ```
  32     ///
  33     /// Use instead:
  34     /// ```no_run
  35     /// enum S {
  36     ///     Pending,
  37     ///     Processing,
  38     ///     Finished,
  39     /// }
  40     /// ```
  41     #[clippy::version = "1.43.0"]
  42     pub STRUCT_EXCESSIVE_BOOLS,
  43     pedantic,
  44     "using too many bools in a struct"
  45 }
  46
  47 declare_clippy_lint! {
  48     /// ### What it does
  49     /// Checks for excessive use of
  50     /// bools in function definitions.
  51     ///
  52     /// ### Why is this bad?
  53     /// Calls to such functions
  54     /// are confusing and error prone, because it's
  55     /// hard to remember argument order and you have
  56     /// no type system support to back you up. Using
  57     /// two-variant enums instead of bools often makes
  58     /// API easier to use.
  59     ///
  60     /// ### Example
  61     /// ```rust,ignore
  62     /// fn f(is_round: bool, is_hot: bool) { ... }
  63     /// ```
  64     ///
  65     /// Use instead:
  66     /// ```rust,ignore
  67     /// enum Shape {
  68     ///     Round,
  69     ///     Spiky,
  70     /// }
  71     ///
  72     /// enum Temperature {
  73     ///     Hot,
  74     ///     IceCold,
  75     /// }
  76     ///
  77     /// fn f(shape: Shape, temperature: Temperature) { ... }
  78     /// ```
  79     #[clippy::version = "1.43.0"]
  80     pub FN_PARAMS_EXCESSIVE_BOOLS,
  81     pedantic,
  82     "using too many bools in function parameters"
  83 }
  84
  85 pub struct ExcessiveBools {
  86     max_struct_bools: u64,
  87     max_fn_params_bools: u64,
  88 }
  89
  90 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
  91 enum Kind {
  92     Struct,
  93     Fn,
  94 }
  95
  96 impl ExcessiveBools {
  97     #[must_use]
  98     pub fn new(max_struct_bools: u64, max_fn_params_bools: u64) -> Self {
  99         Self {
 100             max_struct_bools,
 101             max_fn_params_bools,
 102         }
 103     }
 104
 105     fn too_many_bools<'tcx>(&self, tys: impl Iterator<Item = &'tcx Ty<'tcx>>, kind: Kind) -> bool {
 106         if let Ok(bools) = tys.filter(|ty| is_bool(ty)).count().try_into() {
 107             (if Kind::Fn == kind {
 108                 self.max_fn_params_bools
 109             } else {
 110                 self.max_struct_bools
 111             }) < bools
 112         } else {
 113             false
 114         }
 115     }
 116
 117     fn check_fn_sig(&self, cx: &LateContext<'_>, fn_decl: &FnDecl<'_>, span: Span) {
 118         if !span.from_expansion() && self.too_many_bools(fn_decl.inputs.iter(), Kind::Fn) {
 119             span_lint_and_help(
 120                 cx,
 121                 FN_PARAMS_EXCESSIVE_BOOLS,
 122                 span,
 123                 &format!("more than {} bools in function parameters", self.max_fn_params_bools),
 124                 None,
 125                 "consider refactoring bools into two-variant enums",
 126             );
 127         }
 128     }
 129 }
 130
 131 impl_lint_pass!(ExcessiveBools => [STRUCT_EXCESSIVE_BOOLS, FN_PARAMS_EXCESSIVE_BOOLS]);
 132
 133 impl<'tcx> LateLintPass<'tcx> for ExcessiveBools {
 134     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
 135         if item.span.from_expansion() {
 136             return;
 137         }
 138         if let ItemKind::Struct(variant_data, _) = &item.kind {
 139             if has_repr_attr(cx, item.hir_id()) {
 140                 return;
 141             }
 142
 143             if self.too_many_bools(variant_data.fields().iter().map(|field| field.ty), Kind::Struct) {
 144                 span_lint_and_help(
 145                     cx,
 146                     STRUCT_EXCESSIVE_BOOLS,
 147                     item.span,
 148                     &format!("more than {} bools in a struct", self.max_struct_bools),
 149                     None,
 150                     "consider using a state machine or refactoring bools into two-variant enums",
 151                 );
 152             }
 153         }
 154     }
 155
 156     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, trait_item: &'tcx TraitItem<'tcx>) {
 157         // functions with a body are already checked by `check_fn`
 158         if let TraitItemKind::Fn(fn_sig, TraitFn::Required(_)) = &trait_item.kind
 159             && fn_sig.header.abi == Abi::Rust
 160         {
 161             self.check_fn_sig(cx, fn_sig.decl, fn_sig.span);
 162         }
 163     }
 164
 165     fn check_fn(
 166         &mut self,
 167         cx: &LateContext<'tcx>,
 168         fn_kind: FnKind<'tcx>,
 169         fn_decl: &'tcx FnDecl<'tcx>,
 170         _: &'tcx Body<'tcx>,
 171         span: Span,
 172         def_id: LocalDefId,
 173     ) {
 174         let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
 175         if let Some(fn_header) = fn_kind.header()
 176             && fn_header.abi == Abi::Rust
 177             && get_parent_as_impl(cx.tcx, hir_id).map_or(true, |impl_item| impl_item.of_trait.is_none())
 178         {
 179             self.check_fn_sig(cx, fn_decl, span);
 180         }
 181     }
 182 }