[webkit.RefCntblBaseVirtualDtor] Allow CRTP classes without a virtual destructor.

Exempt CRTP (Curiously Recurring Template Pattern) classes with a delete operation
acting on "this" pointer with an appropriate cast from the requirement that
a ref-countable superclass must have a virtual destructor.

To do this, this PR introduces new DerefAnalysisVisitor, which looks for a delete
operation with an explicit cast to the derived class in a base class.

This PR also changes the checker so that we only check a given class's immediate
base class instead of all ancestor base classes in the class hierarchy. This is
sufficient because the checker will eventually see the definition for every class
in the class hierarchy and transitively proves every ref-counted base class has
a virtual destructor or deref function which casts this pointer back to the derived
class before deleting. Without this change, we would keep traversing the same list
of base classes whenever we encounter a new subclass, which is wholly unnecessary.

It's possible for DerefAnalysisVisitor to come to a conclusoin that there isn't
enough information to determine whether a given templated superclass invokes delete
operation on a subclass when the template isn't fully specialized for the subclass.
In this case, we return std::nullopt in HasSpecializedDelete, and visitCXXRecordDecl
will skip this declaration. This is okay because the checker will eventually see
a concreate fully specialized class definition if it ever gets instantiated.

Author: Ryosuke Niwa

clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp

@@ -11,16 +11,134 @@
 #include "PtrTypesSemantics.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/StmtVisitor.h"
 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetVector.h"
 #include <optional>
 
 using namespace clang;
 using namespace ento;
 
 namespace {
+
+class DerefAnalysisVisitor
+    : public ConstStmtVisitor<DerefAnalysisVisitor, bool> {
+  // Returns true if any of child statements return true.
+  bool VisitChildren(const Stmt *S) {
+    for (const Stmt *Child : S->children()) {
+      if (Child && Visit(Child))
+        return true;
+    }
+    return false;
+  }
+
+  bool VisitBody(const Stmt *Body) {
+    if (!Body)
+      return false;
+
+    auto [It, IsNew] = VisitedBody.insert(Body);
+    if (!IsNew) // This body is recursive
+      return false;
+
+    return Visit(Body);
+  }
+
+public:
+  DerefAnalysisVisitor(const TemplateArgumentList &ArgList,
+                       const CXXRecordDecl *ClassDecl)
+      : ArgList(&ArgList), ClassDecl(ClassDecl) {}
+
+  DerefAnalysisVisitor(const CXXRecordDecl *ClassDecl) : ClassDecl(ClassDecl) {}
+
+  std::optional<bool> HasSpecializedDelete(CXXMethodDecl *Decl) {
+    if (auto *Body = Decl->getBody())
+      return VisitBody(Body);
+    if (auto *Tmpl = Decl->getTemplateInstantiationPattern())
+      return std::nullopt; // Indeterminate. There was no concrete instance.
+    return false;
+  }
+
+  bool VisitCallExpr(const CallExpr *CE) {
+    auto *Callee = CE->getCallee();
+    while (auto *Expr = dyn_cast<CastExpr>(Callee))
+      Callee = Expr->getSubExpr();
+    if (auto *DeclRef = dyn_cast<DeclRefExpr>(Callee)) {
+      auto *Decl = DeclRef->getDecl();
+      if (auto *VD = dyn_cast<VarDecl>(Decl)) {
+        if (auto *Init = VD->getInit()) {
+          if (auto *Lambda = dyn_cast<LambdaExpr>(Init))
+            return VisitBody(Lambda->getBody());
+        }
+      } else if (auto *FD = dyn_cast<FunctionDecl>(Decl))
+        return VisitBody(FD->getBody());
+    }
+    return false;
+  }
+
+  bool VisitCXXMemberCallExpr(const CXXMemberCallExpr *MCE) {
+    auto *Callee = MCE->getMethodDecl();
+    if (!Callee)
+      return false;
+    return VisitBody(Callee->getBody());
+  }
+
+  bool VisitCXXDeleteExpr(const CXXDeleteExpr *E) {
+    auto *Arg = E->getArgument();
+    while (Arg) {
+      if (auto *Paren = dyn_cast<ParenExpr>(Arg))
+        Arg = Paren->getSubExpr();
+      else if (auto *Cast = dyn_cast<CastExpr>(Arg)) {
+        Arg = Cast->getSubExpr();
+        auto CastType = Cast->getType();
+        if (auto *PtrType = dyn_cast<PointerType>(CastType)) {
+          auto PointeeType = PtrType->getPointeeType();
+          while (auto *ET = dyn_cast<ElaboratedType>(PointeeType)) {
+            if (ET->isSugared())
+              PointeeType = ET->desugar();
+          }
+          if (auto *ParmType = dyn_cast<TemplateTypeParmType>(PointeeType)) {
+            if (ArgList) {
+              auto ParmIndex = ParmType->getIndex();
+              auto Type = ArgList->get(ParmIndex).getAsType();
+              if (auto *RD = dyn_cast<RecordType>(Type)) {
+                if (RD->getDecl() == ClassDecl)
+                  return true;
+              }
+            }
+          } else if (auto *RD = dyn_cast<RecordType>(PointeeType)) {
+            if (RD->getDecl() == ClassDecl)
+              return true;
+          } else if (auto *ST =
+                         dyn_cast<SubstTemplateTypeParmType>(PointeeType)) {
+            auto Type = ST->getReplacementType();
+            if (auto *RD = dyn_cast<RecordType>(Type)) {
+              if (RD->getDecl() == ClassDecl)
+                return true;
+            }
+          }
+        }
+      } else
+        break;
+    }
+    return false;
+  }
+
+  bool VisitStmt(const Stmt *S) { return VisitChildren(S); }
+
+  // Return false since the contents of lambda isn't necessarily executed.
+  // If it is executed, VisitCallExpr above will visit its body.
+  bool VisitLambdaExpr(const LambdaExpr *) { return false; }
+
+private:
+  const TemplateArgumentList *ArgList{nullptr};
+  const CXXRecordDecl *ClassDecl;
+  llvm::DenseSet<const Stmt *> VisitedBody;
+};
+
 class RefCntblBaseVirtualDtorChecker
     : public Checker<check::ASTDecl<TranslationUnitDecl>> {
 private:
@@ -51,92 +169,137 @@ class RefCntblBaseVirtualDtorChecker
       bool shouldVisitImplicitCode() const { return false; }
 
       bool VisitCXXRecordDecl(const CXXRecordDecl *RD) {
-        Checker->visitCXXRecordDecl(RD);
+        if (!RD->hasDefinition())
+          return true;
+
+        Decls.insert(RD);
+
+        for (auto &Base : RD->bases()) {
+          const auto AccSpec = Base.getAccessSpecifier();
+          if (AccSpec == AS_protected || AccSpec == AS_private ||
+              (AccSpec == AS_none && RD->isClass()))
+            continue;
+
+          QualType T = Base.getType();
+          if (T.isNull())
+            continue;
+
+          const CXXRecordDecl *C = T->getAsCXXRecordDecl();
+          if (!C)
+            continue;
+
+          if (auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(C)) {
+            auto &Args = CTSD->getTemplateArgs();
+            for (unsigned i = 0; i < Args.size(); ++i) {
+              if (Args[i].getKind() != TemplateArgument::Type)
+                continue;
+              auto TemplT = Args[i].getAsType();
+              if (TemplT.isNull())
+                continue;
+
+              bool IsCRTP = TemplT->getAsCXXRecordDecl() == RD;
+              if (!IsCRTP)
+                continue;
+              CRTPs.insert(C);
+            }
+          }
+        }
+
         return true;
       }
+
+      llvm::SetVector<const CXXRecordDecl *> Decls;
+      llvm::DenseSet<const CXXRecordDecl *> CRTPs;
     };
 
     LocalVisitor visitor(this);
     visitor.TraverseDecl(const_cast<TranslationUnitDecl *>(TUD));
+    for (auto *RD : visitor.Decls) {
+      if (visitor.CRTPs.contains(RD))
+        continue;
+      visitCXXRecordDecl(RD);
+    }
   }
 
   void visitCXXRecordDecl(const CXXRecordDecl *RD) const {
     if (shouldSkipDecl(RD))
       return;
 
-    CXXBasePaths Paths;
-    Paths.setOrigin(RD);
-
-    const CXXBaseSpecifier *ProblematicBaseSpecifier = nullptr;
-    const CXXRecordDecl *ProblematicBaseClass = nullptr;
+    for (auto &Base : RD->bases()) {
+      const auto AccSpec = Base.getAccessSpecifier();
+      if (AccSpec == AS_protected || AccSpec == AS_private ||
+          (AccSpec == AS_none && RD->isClass()))
+        continue;
 
-    const auto IsPublicBaseRefCntblWOVirtualDtor =
-        [RD, &ProblematicBaseSpecifier,
-         &ProblematicBaseClass](const CXXBaseSpecifier *Base, CXXBasePath &) {
-          const auto AccSpec = Base->getAccessSpecifier();
-          if (AccSpec == AS_protected || AccSpec == AS_private ||
-              (AccSpec == AS_none && RD->isClass()))
-            return false;
+      auto hasRefInBase = clang::hasPublicMethodInBase(&Base, "ref");
+      auto hasDerefInBase = clang::hasPublicMethodInBase(&Base, "deref");
 
-          auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
-          auto hasDerefInBase = clang::hasPublicMethodInBase(Base, "deref");
+      bool hasRef = hasRefInBase && *hasRefInBase != nullptr;
+      bool hasDeref = hasDerefInBase && *hasDerefInBase != nullptr;
 
-          bool hasRef = hasRefInBase && *hasRefInBase != nullptr;
-          bool hasDeref = hasDerefInBase && *hasDerefInBase != nullptr;
+      QualType T = Base.getType();
+      if (T.isNull())
+        continue;
 
-          QualType T = Base->getType();
-          if (T.isNull())
-            return false;
+      const CXXRecordDecl *C = T->getAsCXXRecordDecl();
+      if (!C)
+        continue;
 
-          const CXXRecordDecl *C = T->getAsCXXRecordDecl();
-          if (!C)
-            return false;
-          if (isRefCountedClass(C))
-            return false;
-
-          bool AnyInconclusiveBase = false;
-          const auto hasPublicRefInBase =
-              [&AnyInconclusiveBase](const CXXBaseSpecifier *Base,
-                                     CXXBasePath &) {
-                auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
-                if (!hasRefInBase) {
-                  AnyInconclusiveBase = true;
-                  return false;
-                }
-                return (*hasRefInBase) != nullptr;
-              };
-          const auto hasPublicDerefInBase = [&AnyInconclusiveBase](
-                                                const CXXBaseSpecifier *Base,
-                                                CXXBasePath &) {
+      bool AnyInconclusiveBase = false;
+      const auto hasPublicRefInBase =
+          [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
+            auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
+            if (!hasRefInBase) {
+              AnyInconclusiveBase = true;
+              return false;
+            }
+            return (*hasRefInBase) != nullptr;
+          };
+      const auto hasPublicDerefInBase =
+          [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
             auto hasDerefInBase = clang::hasPublicMethodInBase(Base, "deref");
             if (!hasDerefInBase) {
               AnyInconclusiveBase = true;
               return false;
             }
             return (*hasDerefInBase) != nullptr;
           };
-          CXXBasePaths Paths;
-          Paths.setOrigin(C);
-          hasRef = hasRef || C->lookupInBases(hasPublicRefInBase, Paths,
+      CXXBasePaths Paths;
+      Paths.setOrigin(C);
+      hasRef = hasRef || C->lookupInBases(hasPublicRefInBase, Paths,
+                                          /*LookupInDependent =*/true);
+      hasDeref = hasDeref || C->lookupInBases(hasPublicDerefInBase, Paths,
                                               /*LookupInDependent =*/true);
-          hasDeref = hasDeref || C->lookupInBases(hasPublicDerefInBase, Paths,
-                                                  /*LookupInDependent =*/true);
-          if (AnyInconclusiveBase || !hasRef || !hasDeref)
-            return false;
-
-          const auto *Dtor = C->getDestructor();
-          if (!Dtor || !Dtor->isVirtual()) {
-            ProblematicBaseSpecifier = Base;
-            ProblematicBaseClass = C;
-            return true;
-          }
-
-          return false;
-        };
-
-    if (RD->lookupInBases(IsPublicBaseRefCntblWOVirtualDtor, Paths,
-                          /*LookupInDependent =*/true)) {
-      reportBug(RD, ProblematicBaseSpecifier, ProblematicBaseClass);
+      if (AnyInconclusiveBase || !hasRef || !hasDeref)
+        continue;
+
+      auto HasSpecializedDelete = isClassWithSpecializedDelete(C, RD);
+      if (!HasSpecializedDelete || *HasSpecializedDelete)
+        continue;
+      if (C->lookupInBases(
+              [&](const CXXBaseSpecifier *Base, CXXBasePath &) {
+                auto *T = Base->getType().getTypePtrOrNull();
+                if (!T)
+                  return false;
+                auto *R = T->getAsCXXRecordDecl();
+                if (!R)
+                  return false;
+                auto Result = isClassWithSpecializedDelete(R, RD);
+                if (!Result)
+                  AnyInconclusiveBase = true;
+                return Result && *Result;
+              },
+              Paths, /*LookupInDependent =*/true))
+        continue;
+      if (AnyInconclusiveBase)
+        continue;
+
+      const auto *Dtor = C->getDestructor();
+      if (!Dtor || !Dtor->isVirtual()) {
+        auto *ProblematicBaseSpecifier = &Base;
+        auto *ProblematicBaseClass = C;
+        reportBug(RD, ProblematicBaseSpecifier, ProblematicBaseClass);
+      }
     }
   }
 
@@ -182,6 +345,32 @@ class RefCntblBaseVirtualDtorChecker
             ClsName == "ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr");
   }
 
+  static std::optional<bool>
+  isClassWithSpecializedDelete(const CXXRecordDecl *C,
+                               const CXXRecordDecl *DerivedClass) {
+    if (auto *ClsTmplSpDecl = dyn_cast<ClassTemplateSpecializationDecl>(C)) {
+      for (auto *MethodDecl : C->methods()) {
+        if (safeGetName(MethodDecl) == "deref") {
+          DerefAnalysisVisitor DerefAnalysis(ClsTmplSpDecl->getTemplateArgs(),
+                                             DerivedClass);
+          auto Result = DerefAnalysis.HasSpecializedDelete(MethodDecl);
+          if (!Result || *Result)
+            return Result;
+        }
+      }
+      return false;
+    }
+    for (auto *MethodDecl : C->methods()) {
+      if (safeGetName(MethodDecl) == "deref") {
+        DerefAnalysisVisitor DerefAnalysis(DerivedClass);
+        auto Result = DerefAnalysis.HasSpecializedDelete(MethodDecl);
+        if (!Result || *Result)
+          return Result;
+      }
+    }
+    return false;
+  }
+
   void reportBug(const CXXRecordDecl *DerivedClass,
                  const CXXBaseSpecifier *BaseSpec,
                  const CXXRecordDecl *ProblematicBaseClass) const {

clang/test/Analysis/Checkers/WebKit/ref-cntbl-base-virtual-dtor-ref-deref-on-diff-classes.cpp

@@ -19,4 +19,5 @@ struct Derived : Base { };
 
 void foo () {
   Derived d;
+  d.deref();
 }