warn on _Nonnull field initialized with null

Author: cs01

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -13021,6 +13021,11 @@ def note_nullable_return_fix : Note<
 def warn_flow_nullable_assignment : Warning<
   "assigning nullable pointer to nonnull variable %0">,
   InGroup<FlowNullableAssignment>;
+def warn_flow_nullable_field_init : Warning<
+  "initializing nonnull member %0 with null">,
+  InGroup<FlowNullableAssignment>;
+def note_nullable_field_init_fix : Note<
+  "remove '_Nonnull' if this member can be null, or remove the null initializer">;
 def note_nullable_assignment_fix : Note<
   "add a null check before assigning, or change the variable type to "
   "'_Nullable'">;

clang/lib/Sema/SemaDeclCXX.cpp

@@ -4225,6 +4225,19 @@ void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D,
   }
 
   FD->setInClassInitializer(InitExpr.get());
+
+  // Warn when a _Nonnull field is initialized with null.
+  if (FD->getType()->isPointerType()) {
+    auto Nullability = FD->getType()->getNullability();
+    if (Nullability && *Nullability == NullabilityKind::NonNull) {
+      Expr *Init = InitExpr.get()->IgnoreParenImpCasts();
+      if (Init->isNullPointerConstant(Context,
+              Expr::NPC_ValueDependentIsNotNull)) {
+        Diag(Init->getExprLoc(), diag::warn_flow_nullable_field_init) << FD;
+        Diag(Init->getExprLoc(), diag::note_nullable_field_init_fix);
+      }
+    }
+  }
 }
 
 /// Find the direct and/or virtual base specifiers that