Why nextpnr-ice40 complains about unconstraint signal?

[zapta]

When I try to use an external vector of length 1 I get a IO 'LEDS' is unconstrained error. If I use instead a vector of size 2 and above it does work. Any idea what the problem is? As far as I understand, vectors such as output wire [0:0] LEDS of length 1 are legal in Verilog

Below are the constraint file, the Verilog module with the output wire [0:0] LEDS vector of length 1, and the build log with the error.

pinout.pcf

set_io CLK     49

set_io LEDS[0] 45

#set_io LEDS[1] 44

blinky.v

module blinky (
    input  CLK,   
    output wire [0:0] LEDS
    // output wire [1:0] LEDS
);

  reg [23:0] counter = 0;

  always @(posedge CLK) counter <= counter + 1;

  assign LEDS = counter[23:23];
  // assign LEDS = counter[23:22];

endmodule

Build log

yosys -p "synth_ice40 -top blinky -json _build/default/hardware.json" -q blinky.v
nextpnr-ice40 --hx8k --package tq144:4k --json _build/default/hardware.json --asc _build/default/hardware.asc --report _build/default/hardware.pnr --pcf pinout.pcf -q
Warning: unmatched constraint 'LEDS[0]' (on line 4)
ERROR: IO 'LEDS' is unconstrained in PCF (override this error with --pcf-allow-unconstrained)
ERROR: Loading PCF failed.
1 warning, 2 errors
scons: *** [_build/default/hardware.asc] Error 255

[rowanG077]

I suspect this is a bug. A similar bug existed for ECP5: #1036

[zapta]

@rowanG077, it seems to work on ECP5 and fail on ICE40 and Gowin. Where should I file issues for it?

[zapta]

Created an issue here #1628