Adding a comment

Author: marco6

interp/interpreter.go

@@ -427,13 +427,20 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 if err != nil {
 return nil, mem, r.errorAt(inst, err)
 }
+// typecodePtr always point to the numMethod field in the type
+// description struct. The methodSet, when present, comes right
+// before the numMethod field (the compiler doesn't generate
+// method sets for concrete types without methods).
+// Considering that the compiler doesn't emit interface type
+// asserts for interfaces with no methods (as the always succeed)
+// then if the offset is zero, this assert must always fail.
 if typecodePtr.offset() == 0 {
 locals[inst.localIndex] = literalValue{uint8(0)}
 break
 }
 typecodePtrOffset, err := typecodePtr.addOffset(-int64(r.pointerSize))
 if err != nil {
-return nil, mem, r.errorAt(inst, err) // unlikely
+return nil, mem, r.errorAt(inst, err)
 }
 methodSetPtr, err := mem.load(typecodePtrOffset, r.pointerSize).asPointer(r)
 if err != nil {