yosys/tests/verilog/hidden_decl.ys

logger -expect error 'Identifier `\\y. is implicitly declared and `default_nettype is set to none' 1
read_verilog <<EOT
`default_nettype none
module top1;
    wire x;
    generate
        if (1) wire y;
    endgenerate
    assign x = y;
endmodule
EOT