[analyzer] Check for return of nil in ObjC methods with nonnull return type.

Update NullabilityChecker so that it checks return statements in ObjC methods.
Previously it was returning early because methods do not have a function type.

Also update detection of violated parameter _Nonnull preconditions to handle
ObjC methods.

rdar://problem/24200560

llvm-svn: 257938

clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp

@@ -366,27 +366,23 @@ static bool checkPreconditionViolation(ProgramStateRef State, ExplodedNode *N,
   if (!D)
     return false;
 
-  if (const auto *BlockD = dyn_cast<BlockDecl>(D)) {
-    if (checkParamsForPreconditionViolation(BlockD->parameters(), State,
-                                            LocCtxt)) {
-      if (!N->isSink())
-        C.addTransition(State->set<PreconditionViolated>(true), N);
-      return true;
-    }
+  ArrayRef<ParmVarDecl*> Params;
+  if (const auto *BD = dyn_cast<BlockDecl>(D))
+    Params = BD->parameters();
+  else if (const auto *FD = dyn_cast<FunctionDecl>(D))
+    Params = FD->parameters();
+  else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
+    Params = MD->parameters();
+  else
     return false;
-  }
 
-  if (const auto *FuncDecl = dyn_cast<FunctionDecl>(D)) {
-    if (checkParamsForPreconditionViolation(FuncDecl->parameters(), State,
-                                            LocCtxt)) {
+  if (checkParamsForPreconditionViolation(Params, State, LocCtxt)) {
     if (!N->isSink())
       C.addTransition(State->set<PreconditionViolated>(true), N);
     return true;
   }
   return false;
 }
-  return false;
-}
 
 void NullabilityChecker::reportBugIfPreconditionHolds(
     ErrorKind Error, ExplodedNode *N, const MemRegion *Region,
@@ -484,16 +480,20 @@ void NullabilityChecker::checkPreStmt(const ReturnStmt *S,
   if (!RetSVal)
     return;
 
+  QualType RequiredRetType;
   AnalysisDeclContext *DeclCtxt =
       C.getLocationContext()->getAnalysisDeclContext();
-  const FunctionType *FuncType = DeclCtxt->getDecl()->getFunctionType();
-  if (!FuncType)
+  const Decl *D = DeclCtxt->getDecl();
+  if (auto *MD = dyn_cast<ObjCMethodDecl>(D))
+    RequiredRetType = MD->getReturnType();
+  else if (auto *FD = dyn_cast<FunctionDecl>(D))
+    RequiredRetType = FD->getReturnType();
+  else
     return;
 
   NullConstraint Nullness = getNullConstraint(*RetSVal, State);
 
-  Nullability RequiredNullability =
-      getNullabilityAnnotation(FuncType->getReturnType());
+  Nullability RequiredNullability = getNullabilityAnnotation(RequiredRetType);
 
   // If the returned value is null but the type of the expression
   // generating it is nonnull then we will suppress the diagnostic.

clang/test/Analysis/nullability_nullonly.mm

@@ -1,5 +1,21 @@
 // RUN: %clang_cc1 -analyze -analyzer-checker=core,nullability.NullPassedToNonnull,nullability.NullReturnedFromNonnull -verify %s
 
+#define nil 0
+#define BOOL int
+
+@protocol NSObject
++ (id)alloc;
+- (id)init;
+@end
+
+@protocol NSCopying
+@end
+
+__attribute__((objc_root_class))
+@interface
+NSObject<NSObject>
+@end
+
 int getRandom();
 
 typedef struct Dummy { int val; } Dummy;
@@ -85,3 +101,27 @@ Dummy *_Nonnull testDefensiveInlineChecks(Dummy * p) {
     takesNonnull(p);
   return p;
 }
+
+
+@interface SomeClass : NSObject
+@end
+
+@implementation SomeClass (MethodReturn)
+- (SomeClass * _Nonnull)testReturnsNilInNonnull {
+  SomeClass *local = nil;
+  return local; // expected-warning {{Null is returned from a function that is expected to return a non-null value}}
+}
+
+- (SomeClass * _Nonnull)testReturnsCastSuppressedNilInNonnull {
+  SomeClass *local = nil;
+  return (SomeClass * _Nonnull)local; // no-warning
+}
+
+- (SomeClass * _Nonnull)testReturnsNilInNonnullWhenPreconditionViolated:(SomeClass * _Nonnull) p {
+  SomeClass *local = nil;
+  if (!p) // Pre-condition violated here.
+    return local; // no-warning
+  else
+    return p; // no-warning
+}
+@end