128 lines
4.1 KiB
Rust
128 lines
4.1 KiB
Rust
use crate::utils::{
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get_trait_def_id, if_sequence, implements_trait, parent_node_is_if_expr, paths, span_lint_and_help, SpanlessEq,
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};
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use rustc_hir::{BinOpKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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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:** Checks comparison chains written with `if` that can be
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/// rewritten with `match` and `cmp`.
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///
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/// **Why is this bad?** `if` is not guaranteed to be exhaustive and conditionals can get
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/// repetitive
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///
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/// **Known problems:** The match statement may be slower due to the compiler
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/// not inlining the call to cmp. See issue [#5354](https://github.com/rust-lang/rust-clippy/issues/5354)
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///
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/// **Example:**
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/// ```rust,ignore
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/// # fn a() {}
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/// # fn b() {}
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/// # fn c() {}
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/// fn f(x: u8, y: u8) {
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/// if x > y {
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/// a()
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/// } else if x < y {
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/// b()
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/// } else {
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/// c()
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/// }
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/// }
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/// ```
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///
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/// Could be written:
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///
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/// ```rust,ignore
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/// use std::cmp::Ordering;
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/// # fn a() {}
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/// # fn b() {}
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/// # fn c() {}
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/// fn f(x: u8, y: u8) {
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/// match x.cmp(&y) {
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/// Ordering::Greater => a(),
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/// Ordering::Less => b(),
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/// Ordering::Equal => c()
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/// }
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/// }
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/// ```
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pub COMPARISON_CHAIN,
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style,
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"`if`s that can be rewritten with `match` and `cmp`"
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}
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declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
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impl<'tcx> LateLintPass<'tcx> for ComparisonChain {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if expr.span.from_expansion() {
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return;
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}
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// We only care about the top-most `if` in the chain
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if parent_node_is_if_expr(expr, cx) {
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return;
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}
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// Check that there exists at least one explicit else condition
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let (conds, _) = if_sequence(expr);
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if conds.len() < 2 {
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return;
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}
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for cond in conds.windows(2) {
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if let (
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&ExprKind::Binary(ref kind1, ref lhs1, ref rhs1),
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&ExprKind::Binary(ref kind2, ref lhs2, ref rhs2),
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) = (&cond[0].kind, &cond[1].kind)
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{
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if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
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return;
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}
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// Check that both sets of operands are equal
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let mut spanless_eq = SpanlessEq::new(cx);
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let same_fixed_operands = spanless_eq.eq_expr(lhs1, lhs2) && spanless_eq.eq_expr(rhs1, rhs2);
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let same_transposed_operands = spanless_eq.eq_expr(lhs1, rhs2) && spanless_eq.eq_expr(rhs1, lhs2);
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if !same_fixed_operands && !same_transposed_operands {
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return;
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}
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// Check that if the operation is the same, either it's not `==` or the operands are transposed
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if kind1.node == kind2.node {
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if kind1.node == BinOpKind::Eq {
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return;
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}
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if !same_transposed_operands {
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return;
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}
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}
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// Check that the type being compared implements `core::cmp::Ord`
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let ty = cx.typeck_results().expr_ty(lhs1);
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let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
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if !is_ord {
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return;
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}
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} else {
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// We only care about comparison chains
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return;
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}
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}
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span_lint_and_help(
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cx,
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COMPARISON_CHAIN,
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expr.span,
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"`if` chain can be rewritten with `match`",
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None,
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"Consider rewriting the `if` chain to use `cmp` and `match`.",
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)
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}
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}
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fn kind_is_cmp(kind: BinOpKind) -> bool {
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matches!(kind, BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq)
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}
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