rust/clippy_lints/src/excessive_bools.rs

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use crate::utils::{attr_by_name, in_macro, match_path_ast};
use clippy_utils::diagnostics::span_lint_and_help;
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use rustc_ast::ast::{AssocItemKind, Extern, FnKind, FnSig, ImplKind, Item, ItemKind, TraitKind, Ty, TyKind};
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use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::Span;
use std::convert::TryInto;
declare_clippy_lint! {
/// **What it does:** Checks for excessive
/// use of bools in structs.
///
/// **Why is this bad?** Excessive bools in a struct
/// is often a sign that it's used as a state machine,
/// which is much better implemented as an enum.
/// If it's not the case, excessive bools usually benefit
/// from refactoring into two-variant enums for better
/// readability and API.
///
/// **Known problems:** None.
///
/// **Example:**
/// Bad:
/// ```rust
/// struct S {
/// is_pending: bool,
/// is_processing: bool,
/// is_finished: bool,
/// }
/// ```
///
/// Good:
/// ```rust
/// enum S {
/// Pending,
/// Processing,
/// Finished,
/// }
/// ```
pub STRUCT_EXCESSIVE_BOOLS,
pedantic,
"using too many bools in a struct"
}
declare_clippy_lint! {
/// **What it does:** Checks for excessive use of
/// bools in function definitions.
///
/// **Why is this bad?** Calls to such functions
/// are confusing and error prone, because it's
/// hard to remember argument order and you have
/// no type system support to back you up. Using
/// two-variant enums instead of bools often makes
/// API easier to use.
///
/// **Known problems:** None.
///
/// **Example:**
/// Bad:
/// ```rust,ignore
/// fn f(is_round: bool, is_hot: bool) { ... }
/// ```
///
/// Good:
/// ```rust,ignore
/// enum Shape {
/// Round,
/// Spiky,
/// }
///
/// enum Temperature {
/// Hot,
/// IceCold,
/// }
///
/// fn f(shape: Shape, temperature: Temperature) { ... }
/// ```
pub FN_PARAMS_EXCESSIVE_BOOLS,
pedantic,
"using too many bools in function parameters"
}
pub struct ExcessiveBools {
max_struct_bools: u64,
max_fn_params_bools: u64,
}
impl ExcessiveBools {
#[must_use]
pub fn new(max_struct_bools: u64, max_fn_params_bools: u64) -> Self {
Self {
max_struct_bools,
max_fn_params_bools,
}
}
fn check_fn_sig(&self, cx: &EarlyContext<'_>, fn_sig: &FnSig, span: Span) {
match fn_sig.header.ext {
Extern::Implicit | Extern::Explicit(_) => return,
Extern::None => (),
}
let fn_sig_bools = fn_sig
.decl
.inputs
.iter()
.filter(|param| is_bool_ty(&param.ty))
.count()
.try_into()
.unwrap();
if self.max_fn_params_bools < fn_sig_bools {
span_lint_and_help(
cx,
FN_PARAMS_EXCESSIVE_BOOLS,
span,
&format!("more than {} bools in function parameters", self.max_fn_params_bools),
None,
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"consider refactoring bools into two-variant enums",
);
}
}
}
impl_lint_pass!(ExcessiveBools => [STRUCT_EXCESSIVE_BOOLS, FN_PARAMS_EXCESSIVE_BOOLS]);
fn is_bool_ty(ty: &Ty) -> bool {
if let TyKind::Path(None, path) = &ty.kind {
return match_path_ast(path, &["bool"]);
}
false
}
impl EarlyLintPass for ExcessiveBools {
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
if in_macro(item.span) {
return;
}
match &item.kind {
ItemKind::Struct(variant_data, _) => {
if attr_by_name(&item.attrs, "repr").is_some() {
return;
}
let struct_bools = variant_data
.fields()
.iter()
.filter(|field| is_bool_ty(&field.ty))
.count()
.try_into()
.unwrap();
if self.max_struct_bools < struct_bools {
span_lint_and_help(
cx,
STRUCT_EXCESSIVE_BOOLS,
item.span,
&format!("more than {} bools in a struct", self.max_struct_bools),
None,
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"consider using a state machine or refactoring bools into two-variant enums",
);
}
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},
ItemKind::Impl(box ImplKind {
of_trait: None, items, ..
})
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| ItemKind::Trait(box TraitKind(.., items)) => {
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for item in items {
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if let AssocItemKind::Fn(box FnKind(_, fn_sig, _, _)) = &item.kind {
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self.check_fn_sig(cx, fn_sig, item.span);
}
}
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},
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ItemKind::Fn(box FnKind(_, fn_sig, _, _)) => self.check_fn_sig(cx, fn_sig, item.span),
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_ => (),
}
}
}