Suggest using Vec::extend() in same_item_push

Using `Vec::extend(std::iter::repeat_n(item, N))` allows to use the more
natural number of elements to add `N`, as is probably done in the original
loop, instead of computing the difference between the existing number of
elements and the wanted one.

Before MSRV 1.82, the older suggestion to use `Vec::resize()` is still
issued.

tests/ui/same_item_push.rs

@@ -21,33 +21,43 @@ fn main() {
     let item = 2;
     for _ in 5..=20 {
         vec.push(item);
-        //~^ ERROR: it looks like the same item is being pushed into this Vec
+        //~^ ERROR: it looks like the same item is being pushed into this `Vec`
     }
 
     let mut vec: Vec<u8> = Vec::new();
     for _ in 0..15 {
         let item = 2;
         vec.push(item);
-        //~^ ERROR: it looks like the same item is being pushed into this Vec
+        //~^ ERROR: it looks like the same item is being pushed into this `Vec`
     }
 
     let mut vec: Vec<u8> = Vec::new();
     for _ in 0..15 {
         vec.push(13);
-        //~^ ERROR: it looks like the same item is being pushed into this Vec
+        //~^ ERROR: it looks like the same item is being pushed into this `Vec`
     }
 
     let mut vec = Vec::new();
     for _ in 0..20 {
         vec.push(VALUE);
-        //~^ ERROR: it looks like the same item is being pushed into this Vec
+        //~^ ERROR: it looks like the same item is being pushed into this `Vec`
     }
 
     let mut vec = Vec::new();
     let item = VALUE;
     for _ in 0..20 {
         vec.push(item);
-        //~^ ERROR: it looks like the same item is being pushed into this Vec
+        //~^ ERROR: it looks like the same item is being pushed into this `Vec`
+    }
+
+    #[clippy::msrv = "1.81"]
+    fn older_msrv() {
+        let mut vec = Vec::new();
+        let item = VALUE;
+        for _ in 0..20 {
+            vec.push(item);
+            //~^ ERROR: it looks like the same item is being pushed into this `Vec`
+        }
     }
 
     // ** non-linted cases **

tests/ui/same_item_push.stderr

@@ -1,44 +1,58 @@
-error: it looks like the same item is being pushed into this Vec
+error: it looks like the same item is being pushed into this `Vec`
   --> tests/ui/same_item_push.rs:23:9
    |
 LL |         vec.push(item);
    |         ^^^
    |
-   = help: consider using vec![item;SIZE] or vec.resize(NEW_SIZE, item)
+   = help: consider using `vec![item;SIZE]`
+   = help: or `vec.extend(std::iter::repeat_n(item, SIZE))`
    = note: `-D clippy::same-item-push` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::same_item_push)]`
 
-error: it looks like the same item is being pushed into this Vec
+error: it looks like the same item is being pushed into this `Vec`
   --> tests/ui/same_item_push.rs:30:9
    |
 LL |         vec.push(item);
    |         ^^^
    |
-   = help: consider using vec![item;SIZE] or vec.resize(NEW_SIZE, item)
+   = help: consider using `vec![item;SIZE]`
+   = help: or `vec.extend(std::iter::repeat_n(item, SIZE))`
 
-error: it looks like the same item is being pushed into this Vec
+error: it looks like the same item is being pushed into this `Vec`
   --> tests/ui/same_item_push.rs:36:9
    |
 LL |         vec.push(13);
    |         ^^^
    |
-   = help: consider using vec![13;SIZE] or vec.resize(NEW_SIZE, 13)
+   = help: consider using `vec![13;SIZE]`
+   = help: or `vec.extend(std::iter::repeat_n(13, SIZE))`
 
-error: it looks like the same item is being pushed into this Vec
+error: it looks like the same item is being pushed into this `Vec`
   --> tests/ui/same_item_push.rs:42:9
    |
 LL |         vec.push(VALUE);
    |         ^^^
    |
-   = help: consider using vec![VALUE;SIZE] or vec.resize(NEW_SIZE, VALUE)
+   = help: consider using `vec![VALUE;SIZE]`
+   = help: or `vec.extend(std::iter::repeat_n(VALUE, SIZE))`
 
-error: it looks like the same item is being pushed into this Vec
+error: it looks like the same item is being pushed into this `Vec`
   --> tests/ui/same_item_push.rs:49:9
    |
 LL |         vec.push(item);
    |         ^^^
    |
-   = help: consider using vec![item;SIZE] or vec.resize(NEW_SIZE, item)
+   = help: consider using `vec![item;SIZE]`
+   = help: or `vec.extend(std::iter::repeat_n(item, SIZE))`
 
-error: aborting due to 5 previous errors
+error: it looks like the same item is being pushed into this `Vec`
+  --> tests/ui/same_item_push.rs:58:13
+   |
+LL |             vec.push(item);
+   |             ^^^
+   |
+   = help: consider using `vec![item;SIZE]`
+   = help: or `vec.resize(NEW_SIZE, item)`
+
+error: aborting due to 6 previous errors