[clang-tools-extra] [clang-tidy] Added bugprone-exception-rethrow check (PR #86448)

[via cfe-commits]

================
@@ -0,0 +1,50 @@
+//===--- ExceptionRethrowCheck.cpp - clang-tidy ---------------------------===//
+//
+// 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 "ExceptionRethrowCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+namespace {
+AST_MATCHER(VarDecl, isExceptionVariable) { return Node.isExceptionVariable(); }
+} // namespace
+
+void ExceptionRethrowCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      cxxThrowExpr(unless(isExpansionInSystemHeader()),
+                   anyOf(unless(has(expr())),
+                         has(declRefExpr(to(varDecl(isExceptionVariable()))))),
+                   optionally(hasAncestor(cxxCatchStmt().bind("catch"))))
+          .bind("throw"),
+      this);
+}
+
+void ExceptionRethrowCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedThrow = Result.Nodes.getNodeAs<CXXThrowExpr>("throw");
+
+  if (const Expr *ThrownObject = MatchedThrow->getSubExpr()) {
+    diag(MatchedThrow->getThrowLoc(),
+         "throwing a copy of the caught %0 exception, remove the argument to "
+         "throw the original exception object")
+        << ThrownObject->getType().getNonReferenceType();
+    return;
+  }
+
+  const bool HasCatchAnsestor =
+      Result.Nodes.getNodeAs<Stmt>("catch") != nullptr;
+  if (!HasCatchAnsestor) {
+    diag(MatchedThrow->getThrowLoc(),
+         "empty 'throw' outside a catch block without an exception can trigger "
+         "'std::terminate'");
----------------
isuckatcs wrote:

```suggestion
         "empty 'throw' outside a catch block with no operand triggers 'std::terminate()'");
```

According to the standard this always happens, and the check is only enabled if exceptions are enabled, so I think the message should reflect this too.
>[N4917 7.6.18 4] If no exception is presently being handled, evaluating a throw-expression with no operand calls std::
terminate() (14.6.2).

https://github.com/llvm/llvm-project/pull/86448