Check that the method ObjCMessageExpr references isn't null before

passing it to diagnoseDeclFeatureAvailability

rdar://146139827

Author: ahatanaka

clang/lib/Sema/SemaFeatureAvailability.cpp

@@ -78,7 +78,8 @@ class DiagnoseUnguardedFeatureAvailability
   }
 
   bool VisitObjCMessageExpr(ObjCMessageExpr *OME) {
-    diagnoseDeclFeatureAvailability(OME->getMethodDecl(), OME->getBeginLoc());
+    if (auto *MD = OME->getMethodDecl())
+      diagnoseDeclFeatureAvailability(MD, OME->getBeginLoc());
     return true;
   }
 

clang/test/SemaObjC/feature-availability.m

@@ -62,7 +62,7 @@ @interface Derived3 : Base7<Base0 *> // expected-error {{use of 'Base0' requires
 @end
 
 __attribute__((availability(domain:feature1, AVAIL))) // expected-note {{is incompatible with __attribute__((availability(domain:feature1, 0)))}} expected-note 2 {{feature attribute __attribute__((availability(domain:feature1, 0)))}}
-@interface Derived0 : Base0 {
+@interface Derived0 : Base0 { // expected-note {{receiver is instance of class declared here}}
   struct S1 *ivar4;
 }
 @property struct S1 *p0;
@@ -81,6 +81,7 @@ -(void)m0 {
 }
 -(void)m1 {
   self.p1 = 1;
+  [self nonexistentMethod]; // expected-warning {{instance method '-nonexistentMethod' not found (return type defaults to 'id')}}
 }
 @end