Improve the `match_same_arms` doc

[rust.git] / src / copies.rs

diff --git a/src/copies.rs b/src/copies.rs
index 691acad6e9202a96ddebbba3f25c7545be657c0b..b8eb97cbeed59a043d6899fff0e75484d18fa07c 100644 (file)
--- a/src/copies.rs
+++ b/src/copies.rs
@@ -1,5 +1,5 @@
 use rustc::lint::*;
-use rustc::middle::ty;
+use rustc::ty;
 use rustc_front::hir::*;
 use std::collections::HashMap;
 use std::collections::hash_map::Entry;
@@ -38,7 +38,9 @@
 
 /// **What it does:** This lint checks for `match` with identical arm bodies.
 ///
-/// **Why is this bad?** This is probably a copy & paste error.
+/// **Why is this bad?** This is probably a copy & paste error. If arm bodies are the same on
+/// purpose, you can factor them
+/// [using `|`](https://doc.rust-lang.org/book/patterns.html#multiple-patterns).
 ///
 /// **Known problems:** Hopefully none.
 ///
@@ -47,7 +49,7 @@
 /// match foo {
 ///     Bar => bar(),
 ///     Quz => quz(),
-///     Baz => bar(), // <= oups
+///     Baz => bar(), // <= oops
 /// }
 /// ```
 declare_lint! {
@@ -132,13 +134,15 @@ fn lint_match_arms(cx: &LateContext, expr: &Expr) {
     };
 
     let eq = |lhs: &Arm, rhs: &Arm| -> bool {
-        SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
+        // Arms with a guard are ignored, those can’t always be merged together
+        lhs.guard.is_none() && rhs.guard.is_none() &&
+            SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
             // all patterns should have the same bindings
             bindings(cx, &lhs.pats[0]) == bindings(cx, &rhs.pats[0])
     };
 
     if let ExprMatch(_, ref arms, MatchSource::Normal) = expr.node {
-        if let Some((i, j)) = search_same(&**arms, hash, eq) {
+        if let Some((i, j)) = search_same(&arms, hash, eq) {
             span_note_and_lint(cx,
                                MATCH_SAME_ARMS,
                                j.body.span,