[clang-tools-extra] [clang-tidy] Add new check 'bugprone-inconsistent-ifelse-braces' (PR #162361)

[Davide Cunial via cfe-commits]

================
@@ -0,0 +1,35 @@
+// RUN: %check_clang_tidy  -std=c++20-or-later %s readability-inconsistent-ifelse-braces %t
+
+void do_something(const char *) {}
+
+// Positive tests.
+void f(bool b) {
+  if (b) [[likely]] do_something("if-same-line");
+  else {
+  }
+  // CHECK-MESSAGES: :[[@LINE-3]]:9: warning: <message> [readability-inconsistent-ifelse-braces]
+  // CHECK-FIXES: if (b) { {{[[][[]}}likely{{[]][]]}} do_something("if-same-line");
+  // CHECK-FIXES: } else {
----------------
capitan-davide wrote:

I was adding some tests with likely/unlikely attributes but this fix-it seems wrong to me (which is the same applied by `readability-braces-around-statements`). From:

```c++
if (b) [[likely]] do_something("if-same-line");
else {
}
```

To:

```c++
if (b) { [[likely]] do_something("if-same-line");
} else {
}
```

Also [cppreference](https://en.cppreference.com/w/cpp/language/if.html) is not clear on where these attributes should be placed.

What do you think? Are these semanically equivalent?

```c++
[[likely]] if (b) do_something();      // (A)
if (b) [[likely]] do_something();      // (B)
if (b) { [[likely]] do_something(); }  // (C)
```

https://github.com/llvm/llvm-project/pull/162361