[clang-tools-extra] [clang-tidy] Unsafe CRTP check (PR #82403)

[via cfe-commits]

================
@@ -0,0 +1,171 @@
+//===--- UnsafeCrtpCheck.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 "UnsafeCrtpCheck.h"
+#include "../utils/LexerUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+namespace {
+// Finds a node if it's already a bound node.
+AST_MATCHER_P(CXXRecordDecl, isBoundNode, std::string, ID) {
+  return Builder->removeBindings(
+      [&](const ast_matchers::internal::BoundNodesMap &Nodes) {
+        const auto *BoundRecord = Nodes.getNodeAs<CXXRecordDecl>(ID);
+        return BoundRecord != &Node;
+      });
+}
+
+bool hasPrivateConstructor(const CXXRecordDecl *RD) {
+  for (auto &&Ctor : RD->ctors()) {
+    if (Ctor->getAccess() == AS_private)
+      return true;
+  }
+
+  return false;
+}
+
+bool isDerivedParameterBefriended(const CXXRecordDecl *CRTP,
+                                  const NamedDecl *Param) {
+  for (auto &&Friend : CRTP->friends()) {
+    const auto *TTPT =
+        dyn_cast<TemplateTypeParmType>(Friend->getFriendType()->getType());
+
+    if (TTPT && TTPT->getDecl() == Param)
+      return true;
+  }
+
+  return false;
+}
+
+bool isDerivedClassBefriended(const CXXRecordDecl *CRTP,
+                              const CXXRecordDecl *Derived) {
+  for (auto &&Friend : CRTP->friends()) {
+    if (Friend->getFriendType()->getType()->getAsCXXRecordDecl() == Derived)
+      return true;
+  }
+
+  return false;
+}
+
+std::optional<const NamedDecl *>
+getDerivedParameter(const ClassTemplateSpecializationDecl *CRTP,
+                    const CXXRecordDecl *Derived) {
+  size_t Idx = 0;
+  bool Found = false;
+  for (auto &&TemplateArg : CRTP->getTemplateArgs().asArray()) {
+    if (TemplateArg.getKind() == TemplateArgument::Type &&
+        TemplateArg.getAsType()->getAsCXXRecordDecl() == Derived) {
+      Found = true;
+      break;
+    }
+    ++Idx;
+  }
+
+  if (!Found)
+    return std::nullopt;
+
+  return CRTP->getSpecializedTemplate()->getTemplateParameters()->getParam(Idx);
+}
+
+std::vector<FixItHint> hintMakeCtorPrivate(const CXXConstructorDecl *Ctor,
+                                           const std::string &OriginalAccess,
+                                           const SourceManager &SM,
+                                           const LangOptions &LangOpts) {
+  std::vector<FixItHint> Hints;
+
+  Hints.emplace_back(FixItHint::CreateInsertion(
+      Ctor->getBeginLoc().getLocWithOffset(-1), "private:\n"));
+
+  const SourceLocation CtorEndLoc =
+      Ctor->isExplicitlyDefaulted()
+          ? utils::lexer::findNextTerminator(Ctor->getEndLoc(), SM, LangOpts)
+          : Ctor->getEndLoc();
+  Hints.emplace_back(FixItHint::CreateInsertion(
+      CtorEndLoc.getLocWithOffset(1), '\n' + OriginalAccess + ':' + '\n'));
+
+  return Hints;
+}
+} // namespace
+
+void UnsafeCrtpCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      classTemplateSpecializationDecl(
+          decl().bind("crtp"),
+          hasAnyTemplateArgument(refersToType(recordType(hasDeclaration(
+              cxxRecordDecl(isDerivedFrom(cxxRecordDecl(isBoundNode("crtp"))))
+                  .bind("derived")))))),
+      this);
+}
+
+void UnsafeCrtpCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *CRTPInstantiation =
+      Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("crtp");
+  const auto *DerivedRecord = Result.Nodes.getNodeAs<CXXRecordDecl>("derived");
+  const CXXRecordDecl *CRTPDeclaration =
+      CRTPInstantiation->getSpecializedTemplate()->getTemplatedDecl();
+
+  if (!CRTPDeclaration->hasUserDeclaredConstructor()) {
+    const bool IsStruct = CRTPDeclaration->isStruct();
+
+    diag(CRTPDeclaration->getLocation(),
+         "the implicit default constructor of the CRTP is publicly accessible")
+        << CRTPDeclaration
+        << FixItHint::CreateInsertion(
+               CRTPDeclaration->getBraceRange().getBegin().getLocWithOffset(1),
+               (IsStruct ? "\nprivate:\n" : "\n") +
+                   CRTPDeclaration->getNameAsString() + "() = default;\n" +
+                   (IsStruct ? "public:\n" : ""));
+    diag(CRTPDeclaration->getLocation(), "consider making it private",
+         DiagnosticIDs::Note);
----------------
isuckatcs wrote:

See the answer in [a previous discussion](https://github.com/llvm/llvm-project/pull/82403#discussion_r1496412033).

https://github.com/llvm/llvm-project/pull/82403