mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-11-27 23:20:39 +00:00
100 lines
3.6 KiB
Rust
100 lines
3.6 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_context;
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use clippy_utils::ty::implements_trait;
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{Expr, ExprKind, Pat, PatKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::Ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for pattern matchings that can be expressed using equality.
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///
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/// ### Why is this bad?
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///
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/// * It reads better and has less cognitive load because equality won't cause binding.
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/// * It is a [Yoda condition](https://en.wikipedia.org/wiki/Yoda_conditions). Yoda conditions are widely
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/// criticized for increasing the cognitive load of reading the code.
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/// * Equality is a simple bool expression and can be merged with `&&` and `||` and
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/// reuse if blocks
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///
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/// ### Example
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/// ```rust,ignore
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/// if let Some(2) = x {
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/// do_thing();
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/// }
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/// ```
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/// Should be written
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/// ```rust,ignore
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/// if x == Some(2) {
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/// do_thing();
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/// }
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/// ```
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pub EQUATABLE_IF_LET,
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nursery,
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"using pattern matching instead of equality"
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}
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declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]);
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/// detects if pattern matches just one thing
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fn unary_pattern(pat: &Pat<'_>) -> bool {
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fn array_rec(pats: &[Pat<'_>]) -> bool {
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pats.iter().all(unary_pattern)
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}
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match &pat.kind {
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PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => {
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false
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},
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PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
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PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => !etc.is_some() && array_rec(a),
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PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x),
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PatKind::Path(_) | PatKind::Lit(_) => true,
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}
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}
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fn is_structural_partial_eq(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> bool {
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if let Some(def_id) = cx.tcx.lang_items().eq_trait() {
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implements_trait(cx, ty, def_id, &[other.into()])
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} else {
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false
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}
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}
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impl<'tcx> LateLintPass<'tcx> for PatternEquality {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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if_chain! {
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if let ExprKind::Let(pat, exp, _) = expr.kind;
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if unary_pattern(pat);
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let exp_ty = cx.typeck_results().expr_ty(exp);
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let pat_ty = cx.typeck_results().pat_ty(pat);
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if is_structural_partial_eq(cx, exp_ty, pat_ty);
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then {
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let mut applicability = Applicability::MachineApplicable;
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let pat_str = match pat.kind {
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PatKind::Struct(..) => format!(
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"({})",
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snippet_with_context(cx, pat.span, expr.span.ctxt(), "..", &mut applicability).0,
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),
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_ => snippet_with_context(cx, pat.span, expr.span.ctxt(), "..", &mut applicability).0.to_string(),
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};
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span_lint_and_sugg(
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cx,
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EQUATABLE_IF_LET,
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expr.span,
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"this pattern matching can be expressed using equality",
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"try",
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format!(
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"{} == {}",
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snippet_with_context(cx, exp.span, expr.span.ctxt(), "..", &mut applicability).0,
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pat_str,
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),
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applicability,
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);
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}
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}
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}
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}
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