Rollup merge of #83092 - petrochenkov:qspan, r=estebank

[rust.git] / clippy_lints / src / comparison_chain.rs

diff --git a/clippy_lints/src/comparison_chain.rs b/clippy_lints/src/comparison_chain.rs
index 9cbd30542b6bebba37f4bc87066e23be69cd3e28..e309db25995fbfa0f8bf5cbe716765047442e269 100644 (file)
--- a/clippy_lints/src/comparison_chain.rs
+++ b/clippy_lints/src/comparison_chain.rs
@@ -1,10 +1,9 @@
 use crate::utils::{
-    get_trait_def_id, if_sequence, implements_trait, parent_node_is_if_expr, paths, span_help_and_lint, SpanlessEq,
+    get_trait_def_id, if_sequence, implements_trait, parent_node_is_if_expr, paths, span_lint_and_help, SpanlessEq,
 };
-use rustc::declare_lint_pass;
-use rustc::hir::*;
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use rustc_session::declare_tool_lint;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
 
 declare_clippy_lint! {
     /// **What it does:** Checks comparison chains written with `if` that can be
@@ -13,7 +12,8 @@
     /// **Why is this bad?** `if` is not guaranteed to be exhaustive and conditionals can get
     /// repetitive
     ///
-    /// **Known problems:** None.
+    /// **Known problems:** The match statement may be slower due to the compiler
+    /// not inlining the call to cmp. See issue [#5354](https://github.com/rust-lang/rust-clippy/issues/5354)
     ///
     /// **Example:**
     /// ```rust,ignore
@@ -53,8 +53,8 @@
 
 declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ComparisonChain {
-    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
+impl<'tcx> LateLintPass<'tcx> for ComparisonChain {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if expr.span.from_expansion() {
             return;
         }
@@ -82,14 +82,25 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 
                 // Check that both sets of operands are equal
                 let mut spanless_eq = SpanlessEq::new(cx);
-                if (!spanless_eq.eq_expr(lhs1, lhs2) || !spanless_eq.eq_expr(rhs1, rhs2))
-                    && (!spanless_eq.eq_expr(lhs1, rhs2) || !spanless_eq.eq_expr(rhs1, lhs2))
-                {
+                let same_fixed_operands = spanless_eq.eq_expr(lhs1, lhs2) && spanless_eq.eq_expr(rhs1, rhs2);
+                let same_transposed_operands = spanless_eq.eq_expr(lhs1, rhs2) && spanless_eq.eq_expr(rhs1, lhs2);
+
+                if !same_fixed_operands && !same_transposed_operands {
                     return;
                 }
 
+                // Check that if the operation is the same, either it's not `==` or the operands are transposed
+                if kind1.node == kind2.node {
+                    if kind1.node == BinOpKind::Eq {
+                        return;
+                    }
+                    if !same_transposed_operands {
+                        return;
+                    }
+                }
+
                 // Check that the type being compared implements `core::cmp::Ord`
-                let ty = cx.tables.expr_ty(lhs1);
+                let ty = cx.typeck_results().expr_ty(lhs1);
                 let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
 
                 if !is_ord {
@@ -100,19 +111,17 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
                 return;
             }
         }
-        span_help_and_lint(
+        span_lint_and_help(
             cx,
             COMPARISON_CHAIN,
             expr.span,
             "`if` chain can be rewritten with `match`",
-            "Consider rewriting the `if` chain to use `cmp` and `match`.",
+            None,
+            "consider rewriting the `if` chain to use `cmp` and `match`",
         )
     }
 }
 
 fn kind_is_cmp(kind: BinOpKind) -> bool {
-    match kind {
-        BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq => true,
-        _ => false,
-    }
+    matches!(kind, BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq)
 }