Incorrect validation for writeonly image2d uniform declarations in GLSL

[spencerkohan]

I am trying to validate the following shader using Naga:

#version 450

#define WORKGROUP_SIZE 16
layout (local_size_x = WORKGROUP_SIZE, local_size_y = WORKGROUP_SIZE, local_size_z = 1 ) in;

precision highp float;

layout(binding = 2) uniform writeonly image2D outputImage;

void main () {
    ivec2 textureSize = imageSize(outputImage);
    
    if (gl_GlobalInvocationID.x >= textureSize.x || gl_GlobalInvocationID.y >= textureSize.y) {
        return;
    }
    
    ivec2 index = ivec2(gl_GlobalInvocationID.xy);
    vec4 colorOut = vec4(1, 0, 1, 1);
    imageStore(outputImage, index, colorOut);
}

And I get the following validation errors:

image types require a format layout qualifier
Unknown function 'imageStore'

The requirement for a format layout qualifier is incorrect. According to the specification:

mage variables can be declared with a format qualifier; this specifies the format for any read operations done on the image. Therefore, a format qualifier is required if you do not declare the variable with the writeonly memory qualifier. Write-only variables cannot be used as in any reading operations; this includes calling load and atomic (read/modify/write) functions. So if you want to read from an image, you must declare the format.

In other words, the format qualifier should not be required in the presence of writeonly.

[spencerkohan]

I created a PR for this here: gfx-rs/naga#2061