[clang-tools-extra] [clang-tidy] Add check to diagnose coroutine-hostile RAII objects (PR #68738)

[Sam McCall via cfe-commits]

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@@ -0,0 +1,98 @@
+//===--- CoroutineHostileRAII.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 "CoroutineHostileRAIICheck.h"
+#include "../utils/OptionsUtils.h"
+#include "clang/AST/Attr.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/AST/Stmt.h"
+#include "clang/AST/Type.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchersInternal.h"
+#include "clang/Basic/AttrKinds.h"
+#include "clang/Basic/DiagnosticIDs.h"
+
+using namespace clang::ast_matchers;
+namespace clang::tidy::misc {
+namespace {
+using clang::ast_matchers::internal::BoundNodesTreeBuilder;
+
+AST_MATCHER_P(Stmt, forEachPrevStmt, ast_matchers::internal::Matcher<Stmt>,
----------------
sam-mccall wrote:

even for an locally-defined matcher, it would be helpful to have a comment on what this matcher does (the definition of "before" is non-obvious).

I also don't think its contract makes much sense: the definition of `before` excludes this:
```
{
  ; // this EmptyStmt is surely "before"...
}
; // this one
```

This is not just an implementation limitation but important to correctness, because we're really talking about variable scope (*initialized* before, but destroyed after).

But if that's the case, the matcher should also be named differently, and it should yield only `VarDecls`, because what it does doesn't make sense for anything except variables.

https://github.com/llvm/llvm-project/pull/68738