interfaced object nil leak

Interfaced object set to nil (interfaced-object-nil-leak)

An OBJECT reference to a TInterfacedObject descendant is set to nil while it holds a fresh instance. Only an interface reference counts; an object reference holds no count, so nil releases nothing and the instance leaks. OFF by default.

function Build: TThing;      // TThing = class(TInterfacedObject, IThing)
begin
  try
    Result := TThing.Create;
    Result.Load;
  except
    Result := nil;           // finding: the instance leaks. Return IThing, or Free it.
  end;
end;

Running it

drag-lint lint <file> --rule interfaced-object-nil-leak
drag-lint lint-all --db <project.sqlite> --rule interfaced-object-nil-leak

What stays silent

• Result := nil with no instance created before it (the find idiom).
• A reference that may have reached an interface holder first: a bare use (I := T, Sink(T)) or a method call on it (T.Subscribe can hand over Self). In those cases the nil only clears an alias.
• A variable typed as an interface.
• T.Free before the nil.
• if C then X := T.Create else X := nil: the two are on different branches.
• A class whose chain to TInterfacedObject is unknown. The rule reads the same file, then the index.
• A plain class. That is a different leak, and not what this rule is about.