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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_context;
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, LintContext};
use rustc_middle::lint::in_external_macro;
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();
/// }
/// ```
/// Use instead:
/// ```rust,ignore
/// if x == Some(2) {
/// do_thing();
/// }
/// ```
#[clippy::version = "1.57.0"]
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<'tcx>(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 !in_external_macro(cx.sess(), expr.span);
if let ExprKind::Let(let_expr) = expr.kind;
if unary_pattern(let_expr.pat);
let exp_ty = cx.typeck_results().expr_ty(let_expr.init);
let pat_ty = cx.typeck_results().pat_ty(let_expr.pat);
if is_structural_partial_eq(cx, exp_ty, pat_ty);
then {
let mut applicability = Applicability::MachineApplicable;
let pat_str = match let_expr.pat.kind {
PatKind::Struct(..) => format!(
"({})",
snippet_with_context(cx, let_expr.pat.span, expr.span.ctxt(), "..", &mut applicability).0,
),
_ => snippet_with_context(cx, let_expr.pat.span, expr.span.ctxt(), "..", &mut applicability).0.to_string(),
};
span_lint_and_sugg(
cx,
EQUATABLE_IF_LET,
expr.span,
"this pattern matching can be expressed using equality",
"try",
format!(
"{} == {}",
snippet_with_context(cx, let_expr.init.span, expr.span.ctxt(), "..", &mut applicability).0,
pat_str,
),
applicability,
);
}
}
}
}
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