The test program below has type T that embeds type U, which has a go:nointerface method M. When compiled with GOEXPERIMENT=fieldtrack, the type assertion should fail. It correctly fails with -G=0 and GOEXPERIMENT=fieldtrack,unified; but it incorrectly succeeds with -G=3.

package main

func main() {
	var i interface{} = new(T)
	if _, ok := i.(interface{ Bad() }); ok {
		panic("FAIL")
	}
}

type T struct{ U }

type U struct{}

//go:nointerface
func (*U) Bad() {}

Notably, the test passes if func main is moved after the Bad method. Presumably the issue is that we don't call irgen.funcDecl (which currently handles setting types.Field.Nointerface) until after types.ResumeCheckSize. Probably we need to change irgen.typeDecl to set types.Field.Nointerface instead, so that it's already set before any method promotion happens.

Alternatively, maybe we can just get rid of Field.Nointerface in favor of checking Func.Pragma directly. If this works, it seems preferable.

/cc @cuonglm @danscales @randall77