// TODO(adonovan): think about generics, and also generic aliases.
	under := aliases.Unalias(typ)
	// Don't call Underlying unconditionally: although it removes
	// Named and Alias, it also removes TypeParam.
	if n, ok := under.(*types.Named); ok {
		under = n.Underlying()
	}
	switch under := under.(type) {
	case *types.Basic:
		switch {
		case under.Info()&types.IsNumeric != 0:
			return &ast.BasicLit{Kind: token.INT, Value: "0"}

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