[clang] Diagnose dangling issues for the "Container<GSLPointer>" case. (llvm#107213)

This pull request enhances the GSL lifetime analysis to detect
situations where a dangling `Container<GSLPointer>` object is
constructed:

```cpp
std::vector<std::string_view> bad = {std::string()}; // dangling
```

The assignment case is not yet supported, but they will be addressed in
a follow-up.

Fixes llvm#100526 (excluding the `push_back` case).

Author: hokein

clang/docs/ReleaseNotes.rst

@@ -298,6 +298,8 @@ Improvements to Clang's diagnostics
 
 - Clang now warns for u8 character literals used in C23 with ``-Wpre-c23-compat`` instead of ``-Wpre-c++17-compat``.
 
+- Clang now diagnoses cases where a dangling ``GSLOwner<GSLPointer>`` object is constructed, e.g. ``std::vector<string_view> v = {std::string()};`` (#GH100526).
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/AttrDocs.td

@@ -6690,6 +6690,20 @@ When the Owner's lifetime ends, it will consider the Pointer to be dangling.
     P.getInt(); // P is dangling
   }
 
+If a template class is annotated with ``[[gsl::Owner]]``, and the first
+instantiated template argument is a pointer type (raw pointer, or ``[[gsl::Pointer]]``),
+the analysis will consider the instantiated class as a container of the pointer.
+When constructing such an object from a GSL owner object, the analysis will
+assume that the container holds a pointer to the owner object. Consequently,
+when the owner object is destroyed, the pointer will be considered dangling.
+
+.. code-block:: c++
+
+   int f() {
+     std::vector<std::string_view> v = {std::string()}; // v holds a dangling pointer.
+     std::optional<std::string_view> o = std::string(); // o holds a dangling pointer.
+   }
+
 }];
 }
 

clang/lib/Sema/CheckExprLifetime.cpp

@@ -267,6 +267,26 @@ static bool isInStlNamespace(const Decl *D) {
   return DC->isStdNamespace();
 }
 
+// Returns true if the given Record decl is a form of `GSLOwner<Pointer>`
+// type, e.g. std::vector<string_view>, std::optional<string_view>.
+static bool isContainerOfPointer(const RecordDecl *Container) {
+  if (const auto *CTSD =
+          dyn_cast_if_present<ClassTemplateSpecializationDecl>(Container)) {
+    if (!CTSD->hasAttr<OwnerAttr>()) // Container must be a GSL owner type.
+      return false;
+    const auto &TAs = CTSD->getTemplateArgs();
+    return TAs.size() > 0 && TAs[0].getKind() == TemplateArgument::Type &&
+           (isRecordWithAttr<PointerAttr>(TAs[0].getAsType()) ||
+            TAs[0].getAsType()->isPointerType());
+  }
+  return false;
+}
+
+static bool isGSLOwner(QualType T) {
+  return isRecordWithAttr<OwnerAttr>(T) &&
+         !isContainerOfPointer(T->getAsRecordDecl());
+}
+
 static bool shouldTrackImplicitObjectArg(const CXXMethodDecl *Callee) {
   if (auto *Conv = dyn_cast_or_null<CXXConversionDecl>(Callee))
     if (isRecordWithAttr<PointerAttr>(Conv->getConversionType()))
@@ -275,7 +295,7 @@ static bool shouldTrackImplicitObjectArg(const CXXMethodDecl *Callee) {
     return false;
   if (!isRecordWithAttr<PointerAttr>(
           Callee->getFunctionObjectParameterType()) &&
-      !isRecordWithAttr<OwnerAttr>(Callee->getFunctionObjectParameterType()))
+      !isGSLOwner(Callee->getFunctionObjectParameterType()))
     return false;
   if (Callee->getReturnType()->isPointerType() ||
       isRecordWithAttr<PointerAttr>(Callee->getReturnType())) {
@@ -413,7 +433,7 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
     // Once we initialized a value with a non gsl-owner reference, it can no
     // longer dangle.
     if (ReturnType->isReferenceType() &&
-        !isRecordWithAttr<OwnerAttr>(ReturnType->getPointeeType())) {
+        !isGSLOwner(ReturnType->getPointeeType())) {
       for (const IndirectLocalPathEntry &PE : llvm::reverse(Path)) {
         if (PE.Kind == IndirectLocalPathEntry::GslReferenceInit ||
             PE.Kind == IndirectLocalPathEntry::LifetimeBoundCall)
@@ -468,12 +488,17 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
     if (CheckCoroCall || Callee->getParamDecl(I)->hasAttr<LifetimeBoundAttr>())
       VisitLifetimeBoundArg(Callee->getParamDecl(I), Args[I]);
     else if (EnableGSLAnalysis && I == 0) {
+      // Perform GSL analysis for the first argument
       if (shouldTrackFirstArgument(Callee)) {
         VisitGSLPointerArg(Callee, Args[0]);
-      } else if (auto *CCE = dyn_cast<CXXConstructExpr>(Call);
-                 CCE &&
-                 CCE->getConstructor()->getParent()->hasAttr<PointerAttr>()) {
-        VisitGSLPointerArg(CCE->getConstructor(), Args[0]);
+      } else if (auto *Ctor = dyn_cast<CXXConstructExpr>(Call)) {
+        const auto *ClassD = Ctor->getConstructor()->getParent();
+        // Two cases:
+        //  a GSL pointer, e.g. std::string_view
+        //  a container of GSL pointer, e.g. std::vector<string_view>
+        if (ClassD->hasAttr<PointerAttr>() ||
+            (isContainerOfPointer(ClassD) && Callee->getNumParams() == 1))
+          VisitGSLPointerArg(Ctor->getConstructor(), Args[0]);
       }
     }
   }
@@ -990,13 +1015,12 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         //   int &p = *localUniquePtr;
         //   someContainer.add(std::move(localUniquePtr));
         //   return p;
-        IsLocalGslOwner = isRecordWithAttr<OwnerAttr>(L->getType());
+        IsLocalGslOwner = isGSLOwner(L->getType());
         if (pathContainsInit(Path) || !IsLocalGslOwner)
           return false;
       } else {
         IsGslPtrValueFromGslTempOwner =
-            MTE && !MTE->getExtendingDecl() &&
-            isRecordWithAttr<OwnerAttr>(MTE->getType());
+            MTE && !MTE->getExtendingDecl() && isGSLOwner(MTE->getType());
         // Skipping a chain of initializing gsl::Pointer annotated objects.
         // We are looking only for the final source to find out if it was
         // a local or temporary owner or the address of a local variable/param.

clang/test/Sema/warn-lifetime-analysis-nocfg.cpp

@@ -158,17 +158,30 @@ auto begin(C &c) -> decltype(c.begin());
 template<typename T, int N>
 T *begin(T (&array)[N]);
 
+using size_t = decltype(sizeof(0));
+
+template<typename T>
+struct initializer_list {
+  const T* ptr; size_t sz;
+};
 template <typename T>
 struct vector {
   typedef __gnu_cxx::basic_iterator<T> iterator;
   iterator begin();
   iterator end();
   const T *data() const;
+  vector();
+  vector(initializer_list<T> __l);
+  
+  template<typename InputIterator>
+	vector(InputIterator first, InputIterator __last);
+
   T &at(int n);
 };
 
 template<typename T>
 struct basic_string_view {
+  basic_string_view();
   basic_string_view(const T *);
   const T *begin() const;
 };
@@ -203,11 +216,21 @@ template<typename T>
 struct optional {
   optional();
   optional(const T&);
+
+  template<typename U = T>
+	optional(U&& t);
+
+  template<typename U>
+	optional(optional<U>&& __t);
+
   T &operator*() &;
   T &&operator*() &&;
   T &value() &;
   T &&value() &&;
 };
+template<typename T>
+optional<__decay(T)> make_optional(T&&);
+
 
 template<typename T>
 struct stack {
@@ -553,3 +576,57 @@ void test() {
   std::string_view svjkk1 = ReturnStringView(StrCat("bar", "x")); // expected-warning {{object backing the pointer will be destroyed at the end of the full-expression}}
 }
 } // namespace GH100549
+
+namespace GH100526 {
+void test() {
+  std::vector<std::string_view> v1({std::string()}); // expected-warning {{object backing the pointer will be destroyed at the end}}
+  std::vector<std::string_view> v2({
+    std::string(), // expected-warning {{object backing the pointer will be destroyed at the end}}
+    std::string_view()
+  });
+  std::vector<std::string_view> v3({
+    std::string_view(),
+    std::string()  // expected-warning {{object backing the pointer will be destroyed at the end}}
+  });
+
+  std::optional<std::string_view> o1 = std::string(); // expected-warning {{object backing the pointer}}
+
+  std::string s;
+  // This is a tricky use-after-free case, what it does:
+  //   1. make_optional creates a temporary "optional<string>"" object
+  //   2. the temporary object owns the underlying string which is copied from s.
+  //   3. the t3 object holds the view to the underlying string of the temporary object.
+  std::optional<std::string_view> o2 = std::make_optional(s); // expected-warning {{object backing the pointer}}
+  std::optional<std::string_view> o3 = std::optional<std::string>(s); // expected-warning {{object backing the pointer}}
+  std::optional<std::string_view> o4 = std::optional<std::string_view>(s); 
+
+  // FIXME: should work for assignment cases
+  v1 = {std::string()};
+  o1 = std::string();
+
+  // no warning on copying pointers.
+  std::vector<std::string_view> n1 = {std::string_view()};
+  std::optional<std::string_view> n2 = {std::string_view()};
+  std::optional<std::string_view> n3 = std::string_view();
+  std::optional<std::string_view> n4 = std::make_optional(std::string_view());
+  const char* b = "";
+  std::optional<std::string_view> n5 = std::make_optional(b);
+  std::optional<std::string_view> n6 = std::make_optional("test");
+}
+
+std::vector<std::string_view> test2(int i) {
+  std::vector<std::string_view> t;
+  if (i)
+    return t; // this is fine, no dangling
+  return std::vector<std::string_view>(t.begin(), t.end());
+}
+
+std::optional<std::string_view> test3(int i) {
+  std::string s;
+  std::string_view sv;
+  if (i)
+   return s; // expected-warning {{address of stack memory associated}}
+  return sv; // fine
+}
+
+} // namespace GH100526