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

[Oliver Hunt via cfe-commits]

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@@ -0,0 +1,63 @@
+
+//===----------------------------------------------------------------------===//
+//
+// 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 "clang/AST/ASTTypeTraits.h"
+#include "clang/AST/Stmt.h"
+#include "clang/ASTMatchers/ASTMatchFinder.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;
+
+  const Stmt *const Else = If->getElse();
+  if (const auto *NestedIf = dyn_cast<const IfStmt>(Else))
+    return shouldHaveBraces(NestedIf);
+
+  return isa<CompoundStmt>(Else);
+}
+
+/// Check that all branchs of the \p If statement is are \c CompoundStmt.
+static bool doesHaveBraces(const IfStmt *If) {
+  const Stmt *const Then = If->getThen();
+  if (!isa<CompoundStmt>(Then))
+    return false;
+
+  const Stmt *const Else = If->getElse();
+  if (const auto *NestedIf = dyn_cast<const IfStmt>(Else))
+    return doesHaveBraces(NestedIf);
+
+  return isa<CompoundStmt>(Else);
+}
+
+void InconsistentIfelseBracesCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      traverse(TK_IgnoreUnlessSpelledInSource,
+               ifStmt(hasElse(anything()), unless(hasParent(ifStmt())))
+                   .bind("if_stmt")),
+      this);
+}
+
+void InconsistentIfelseBracesCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *MatchedIf = Result.Nodes.getNodeAs<IfStmt>("if_stmt");
+
+  if (shouldHaveBraces(MatchedIf) && !doesHaveBraces(MatchedIf)) {
----------------
ojhunt wrote:

nit: llvm style is a single statement should not have a brace - hilariously violating this check (different code bases have differing policies so that's not a strike against this check :D)

I realize this is a draft but I saw it while going through open PRs and was wondering what you were diagnosing :)

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