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Author: serenity4

Compiler/src/abstractinterpretation.jl

@@ -2675,6 +2675,8 @@ function abstract_call_known(interp::AbstractInterpreter, @nospecialize(f),
                     end
                 end
             elseif f === setfield! && length(argtypes) == 4 && isa(argtypes[3], Const)
+                # from there on we know that the struct field will never be undefined,
+                # so we try to encode that information with a `PartialStruct`
                 farg2 = ssa_def_slot(fargs[2], sv)
                 if farg2 isa SlotNumber
                     refined = form_partially_defined_struct(argtypes[2], argtypes[3])