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Original file line number | Diff line number | Diff line change |
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use clippy_utils::diagnostics::span_lint_and_sugg; | ||
use clippy_utils::source::snippet_with_applicability; | ||
use clippy_utils::ty::implements_trait; | ||
use if_chain::if_chain; | ||
use rustc_errors::Applicability; | ||
use rustc_hir::{Expr, ExprKind, Pat, PatKind}; | ||
use rustc_lint::{LateContext, LateLintPass}; | ||
use rustc_middle::ty::Ty; | ||
use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
|
||
declare_clippy_lint! { | ||
/// ### What it does | ||
/// Checks for pattern matchings that can be expressed using equality. | ||
/// | ||
/// ### Why is this bad? | ||
/// | ||
/// * It reads better and has less cognitive load because equality won't cause binding. | ||
/// * It is a [Yoda condition](https://en.wikipedia.org/wiki/Yoda_conditions). Yoda conditions are widely | ||
/// criticized for increasing the cognitive load of reading the code. | ||
/// * Equality is a simple bool expression and can be merged with `&&` and `||` and | ||
/// reuse if blocks | ||
/// | ||
/// ### Example | ||
/// ```rust,ignore | ||
/// if let Some(2) = x { | ||
/// do_thing(); | ||
/// } | ||
/// ``` | ||
/// Should be written | ||
/// ```rust,ignore | ||
/// if x == Some(2) { | ||
/// do_thing(); | ||
/// } | ||
/// ``` | ||
pub EQUATABLE_IF_LET, | ||
nursery, | ||
"using pattern matching instead of equality" | ||
} | ||
|
||
declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]); | ||
|
||
/// detects if pattern matches just one thing | ||
fn unary_pattern(pat: &Pat<'_>) -> bool { | ||
fn array_rec(pats: &[Pat<'_>]) -> bool { | ||
pats.iter().all(unary_pattern) | ||
} | ||
match &pat.kind { | ||
PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => { | ||
false | ||
}, | ||
PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)), | ||
PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => !etc.is_some() && array_rec(a), | ||
PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x), | ||
PatKind::Path(_) | PatKind::Lit(_) => true, | ||
} | ||
} | ||
|
||
fn is_structural_partial_eq(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> bool { | ||
if let Some(def_id) = cx.tcx.lang_items().eq_trait() { | ||
implements_trait(cx, ty, def_id, &[other.into()]) | ||
} else { | ||
false | ||
} | ||
} | ||
|
||
impl<'tcx> LateLintPass<'tcx> for PatternEquality { | ||
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { | ||
if_chain! { | ||
if let ExprKind::Let(pat, exp, _) = expr.kind; | ||
if unary_pattern(pat); | ||
let exp_ty = cx.typeck_results().expr_ty(exp); | ||
let pat_ty = cx.typeck_results().pat_ty(pat); | ||
if is_structural_partial_eq(cx, exp_ty, pat_ty); | ||
then { | ||
|
||
let mut applicability = Applicability::MachineApplicable; | ||
let pat_str = match pat.kind { | ||
PatKind::Struct(..) => format!( | ||
"({})", | ||
snippet_with_applicability(cx, pat.span, "..", &mut applicability), | ||
), | ||
_ => snippet_with_applicability(cx, pat.span, "..", &mut applicability).to_string(), | ||
}; | ||
span_lint_and_sugg( | ||
cx, | ||
EQUATABLE_IF_LET, | ||
expr.span, | ||
"this pattern matching can be expressed using equality", | ||
"try", | ||
format!( | ||
"{} == {}", | ||
snippet_with_applicability(cx, exp.span, "..", &mut applicability), | ||
pat_str, | ||
), | ||
applicability, | ||
); | ||
} | ||
} | ||
} | ||
} |
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