Added branches_sharing_code fp test and note to lint doc `rust-clip…

…py#7452`

clippy_lints/src/copies.rs

@@ -120,7 +120,10 @@ declare_clippy_lint! {
     ///
     /// **Why is this bad?** Duplicate code is less maintainable.
     ///
-    /// **Known problems:** Hopefully none.
+    /// **Known problems:**
+    /// * The lint doesn't check if the moved expressions modify values that are beeing used in
+    ///   the if condition. The suggestion can in that case modify the behavior of the program.
+    ///   See [rust-clippy#7452](https://github.com/rust-lang/rust-clippy/issues/7452)
     ///
     /// **Example:**
     /// ```ignore

tests/ui/branches_sharing_code/false_positives.rs

@@ -25,4 +25,24 @@ impl FooBar {
     fn baz(&mut self) {}
 }
 
+// #########################
+// # Issue 7452
+// #########################
+fn test() {
+    let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 0];
+    let mut counter = 0;
+    for i in v {
+        if counter == 0 {
+            counter += 1;
+            println!("first");
+        } else if counter == 1 {
+            counter += 1;
+            println!("second");
+        } else {
+            counter += 1;
+            println!("other: {}", i);
+        }
+    }
+}
+
 fn main() {}

tests/ui/branches_sharing_code/false_positives.stderr

@@ -0,0 +1,20 @@
+error: all if blocks contain the same code at the start
+  --> $DIR/false_positives.rs:35:9
+   |
+LL | /         if counter == 0 {
+LL | |             counter += 1;
+   | |_________________________^
+   |
+note: the lint level is defined here
+  --> $DIR/false_positives.rs:2:36
+   |
+LL | #![deny(clippy::if_same_then_else, clippy::branches_sharing_code)]
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider moving the start statements out like this
+   |
+LL |         counter += 1;
+LL |         if counter == 0 {
+   |
+
+error: aborting due to previous error
+