[clang-tools-extra] [clang-tidy] Add new check readability-trailing-comma (PR #173669)

[Victor Chernyakin via cfe-commits]

================
@@ -0,0 +1,40 @@
+// RUN: %check_clang_tidy %s readability-trailing-comma %t -- \
+// RUN:   -config='{CheckOptions: {readability-trailing-comma.InitListThreshold: 1}}'
+
+enum Color { Red, Green, Blue };
+// CHECK-MESSAGES: :[[@LINE-1]]:30: warning: enum should have a trailing comma
+// CHECK-FIXES: enum Color { Red, Green, Blue, };
+
+enum SingleValue { Only };
+// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: enum should have a trailing comma
+// CHECK-FIXES: enum SingleValue { Only, };
+
+int arr[] = {1, 2, 3};
+// CHECK-MESSAGES: :[[@LINE-1]]:21: warning: initializer list should have a trailing comma
+// CHECK-FIXES: int arr[] = {1, 2, 3,};
+
+struct Point {
+  int x;
+  int y;
+};
+
+struct Point p = {10, 20};
+// CHECK-MESSAGES: :[[@LINE-1]]:25: warning: initializer list should have a trailing comma
+// CHECK-FIXES: struct Point p = {10, 20,};
+
+struct Point p2 = {.x = 1, .y = 2};
+// CHECK-MESSAGES: :[[@LINE-1]]:34: warning: initializer list should have a trailing comma
+// CHECK-FIXES: struct Point p2 = {.x = 1, .y = 2,};
+
+struct Point p3 = {.x = 5, 10};
+// CHECK-MESSAGES: :[[@LINE-1]]:30: warning: initializer list should have a trailing comma
+// CHECK-FIXES: struct Point p3 = {.x = 5, 10,};
+
+int arr2[5] = {[0] = 1, [4] = 5};
+// CHECK-MESSAGES: :[[@LINE-1]]:32: warning: initializer list should have a trailing comma
+// CHECK-FIXES: int arr2[5] = {[0] = 1, [4] = 5,};
+
+int matrix[2][2] = {{1, 2}, {3, 4}};
+// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: initializer list should have a trailing comma
+// CHECK-MESSAGES: :[[@LINE-2]]:34: warning: initializer list should have a trailing comma
+// CHECK-MESSAGES: :[[@LINE-3]]:35: warning: initializer list should have a trailing comma
----------------
localspook wrote:

Maybe add a `// CHECK-FIXES`?
```suggestion
// CHECK-MESSAGES: :[[@LINE-3]]:35: warning: initializer list should have a trailing comma
// CHECK-FIXES: int matrix[2][2] = {{1, 2,}, {3, 4,},};
```

https://github.com/llvm/llvm-project/pull/173669