Auto merge of #8862 - Alexendoo:get-last-with-len, r=Jarcho,xFrednet

[rust.git] / clippy_lints / src / methods / mod.rs

diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 5102fa17a67e5ecda6a3866ff24ab6066bce0376..b820b7409304562ce75a4d7045e571eb393b2770 100644 (file)
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -21,6 +21,7 @@
 mod flat_map_identity;
 mod flat_map_option;
 mod from_iter_instead_of_collect;
+mod get_last_with_len;
 mod get_unwrap;
 mod implicit_clone;
 mod inefficient_to_string;
@@ -1210,6 +1211,38 @@
     "replace `.drain(..)` with `.into_iter()`"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for using `x.get(x.len() - 1)` instead of
+    /// `x.last()`.
+    ///
+    /// ### Why is this bad?
+    /// Using `x.last()` is easier to read and has the same
+    /// result.
+    ///
+    /// Note that using `x[x.len() - 1]` is semantically different from
+    /// `x.last()`.  Indexing into the array will panic on out-of-bounds
+    /// accesses, while `x.get()` and `x.last()` will return `None`.
+    ///
+    /// There is another lint (get_unwrap) that covers the case of using
+    /// `x.get(index).unwrap()` instead of `x[index]`.
+    ///
+    /// ### Example
+    /// ```rust
+    /// // Bad
+    /// let x = vec![2, 3, 5];
+    /// let last_element = x.get(x.len() - 1);
+    ///
+    /// // Good
+    /// let x = vec![2, 3, 5];
+    /// let last_element = x.last();
+    /// ```
+    #[clippy::version = "1.37.0"]
+    pub GET_LAST_WITH_LEN,
+    complexity,
+    "Using `x.get(x.len() - 1)` when `x.last()` is correct and simpler"
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for use of `.get().unwrap()` (or
@@ -1564,7 +1597,7 @@
     #[clippy::version = "1.39.0"]
     pub MANUAL_SATURATING_ARITHMETIC,
     style,
-    "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
+    "`.checked_add/sub(x).unwrap_or(MAX/MIN)`"
 }
 
 declare_clippy_lint! {
@@ -1777,8 +1810,6 @@
     ///
     /// ### Example
     /// ```rust
-    /// use std::iter::FromIterator;
-    ///
     /// let five_fives = std::iter::repeat(5).take(5);
     ///
     /// let v = Vec::from_iter(five_fives);
@@ -2285,6 +2316,7 @@ pub fn new(
     BYTES_NTH,
     ITER_SKIP_NEXT,
     GET_UNWRAP,
+    GET_LAST_WITH_LEN,
     STRING_EXTEND_CHARS,
     ITER_CLONED_COLLECT,
     ITER_WITH_DRAIN,
@@ -2612,6 +2644,7 @@ fn check_methods<'tcx>(&self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
                         inspect_for_each::check(cx, expr, span2);
                     }
                 },
+                ("get", [arg]) => get_last_with_len::check(cx, expr, recv, arg),
                 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
                 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
                 ("is_digit", [radix]) => is_digit_ascii_radix::check(cx, expr, recv, radix, self.msrv),