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

[Davide Cunial via cfe-commits]

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@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "InconsistentIfelseBracesCheck.h"
+#include "../utils/BracesAroundStatement.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+/// Check that at least one branch of the \p If statement is a \c CompoundStmt.
+static bool shouldHaveBraces(const IfStmt *If) {
+  const Stmt *const Then = If->getThen();
+  if (isa<CompoundStmt>(Then))
+    return true;
+
+  if (const Stmt *const Else = If->getElse()) {
+    if (const auto *NestedIf = dyn_cast<const IfStmt>(Else))
+      return shouldHaveBraces(NestedIf);
+
+    return isa<CompoundStmt>(Else);
+  }
+
+  return false;
+}
+
+void InconsistentIfelseBracesCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      traverse(TK_IgnoreUnlessSpelledInSource,
+               ifStmt(hasElse(anything()),
+                      unless(isConsteval()), // 'if consteval' always has braces
+                      unless(hasParent(ifStmt())))
+                   .bind("if_stmt")),
----------------
capitan-davide wrote:

There is a test for this [here](https://github.com/llvm/llvm-project/pull/162361/files/40570f986a7bec192db25c1001294ca8f93d4c75#diff-44527a85c21f5dc54a69873c1f9f83cdae752651ea62ae152809059d935110a1R77-R83). Basically, the matcher will match the outer `IfStmt` and if the then-branch is another `IfStmt` is handled recursively by [`InconsistentIfelseBracesCheck::checkIfStmt`](https://github.com/llvm/llvm-project/pull/162361/files#diff-1c1e936a6e93dcab49626522a8166d7bfee991f7410e755cecbb60243aae9fa9R60)

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