[analyzer] Do not try to body-farm bodies for Objective-C properties with custom accessors.

[NoQ]

Summary

If a property is defined with a custom getter, we should not behave as if the getter simply returns an instance variable. We don't support setters, so they aren't affected.

On top of being the right thing to do, this also fixes a crash on the newly added test - in which a property and its getter are defined in two separate categories.

[george.karpenkov]

LG, but it sounds like something which can skew results a lot (?)

[NoQ]

Yeah, i'll be testing this.

[NoQ]

Nope, it doesn't seem to skew results at all. I hope my testing machinery is actually working :/

lib/Analysis/BodyFarm.cpp

 
 Stmt *BodyFarm::getBody(const ObjCMethodDecl *D) {
   // We currently only know how to synthesize property accessors.
   if (!D->isPropertyAccessor())
     return nullptr;
 
   D = D->getCanonicalDecl();
 
+  // We should not try to synthesize explicitly redefined accessors.
+  // We do not know for sure how they behave.
+  if (!D->isImplicit())
+    return nullptr;
+
   Optional<Stmt *> &Val = Bodies[D];
   if (Val.hasValue())
     return Val.getValue();
   Val = nullptr;
 
   const ObjCPropertyDecl *Prop = D->findPropertyDecl();
   if (!Prop)
     return nullptr;

test/Analysis/properties.m

void testNoCrashWhenAccessPropertyAndThereAreNoDirectBindingsAtAll() {
    union {
     Wrapper *wrapper;
    } u = { 0 };
    [u.wrapper value];
 }
 
 #endif // non-ARC
 
+@interface ExplicitAccessorInCategory : NSObject
+@property(readonly) int normal;
+- (int)normal;
+@property(readonly) int no_custom_accessor;
+@end
+
+@interface ExplicitAccessorInCategory ()
+@property(readonly) int in_category;
+
+@property(readonly) int still_no_custom_accessor;
+// This is an ordinary method, not a getter.
+- (int)still_no_custom_accessor;
+@end
+
+@interface ExplicitAccessorInCategory ()
+- (int)in_category;
+
+// This is an ordinary method, not a getter.
+- (int)no_custom_accessor;
+@end
+
+@implementation ExplicitAccessorInCategory
+- (void)foo {
+  // Make sure we don't farm bodies for explicit accessors: in particular,
+  // we're not sure that the accessor always returns the same value.
+  clang_analyzer_eval(self.normal == self.normal); // expected-warning{{UNKNOWN}}
+  // Also this used to crash.
+  clang_analyzer_eval(self.in_category == self.in_category); // expected-warning{{UNKNOWN}}
+
+  // When there is no explicit accessor defined (even if it looks like there is),
+  // farm the getter body and see if it does actually always yield the same value.
+  clang_analyzer_eval(self.no_custom_accessor == self.no_custom_accessor); // expected-warning{{TRUE}}
+  clang_analyzer_eval(self.still_no_custom_accessor == self.still_no_custom_accessor); // expected-warning{{TRUE}}
+}
+@end