[clang-tools-extra] [clang-tidy] Add new check 'misc-scope-reduction' (PR #175429)

[via cfe-commits]

================
@@ -0,0 +1,181 @@
+// RUN: %check_clang_tidy %s misc-scope-reduction %t -- --
+
+// Test case 1: Variable can be moved to smaller scope (if-block)
+void test_if_scope() {
+  int x = 42; // CHECK-MESSAGES: :[[@LINE]]:7: warning: variable 'x' can be declared in a smaller scope
----------------
zeyi2 wrote:

Can we put the `// CHECK-MESSAGES` on a new line? 

```suggestion
  int x = 42;
  // CHECK-MESSAGES: :[[@LINE]]:7: warning: variable 'x' can be declared in a smaller scope
```

Same as below.

https://github.com/llvm/llvm-project/pull/175429