So happy to see that timestamp_period going away.

I am sadly still getting "map callback was leaked" errors, plus "failed to get surface texture: Timeout" on my Windows 10, AMD 5700 XT system. That may be some kind of problem with my setup, though it did work with wgpu 0.16 as I recall.

Further, it is breaking Metal.

Caused by:
    In Device::create_compute_pipeline
      note: label = `fine`
    Internal error: Metal: program_source:454:16: error: use of undeclared identifier '_e7'
    float fb = _e7;

Doing a little bit of digging, that's this this fragment of blend.wgsl:

// Apply general compositing operation.
// Inputs are separated colors and alpha, output is premultiplied.
fn blend_compose(
    cb: vec3<f32>,
    cs: vec3<f32>,
    ab: f32,
    as_: f32,
    mode: u32
) -> vec4<f32> {
    var fa = 0.0;
    var fb = 0.0;
    switch mode {

being compiled to this:

metal::float4 blend_compose(
    metal::float3 cb_6,
    metal::float3 cs_6,
    float ab,
    float as,
    uint mode_1
) {
    float fa = 0.0;
    float fb = _e7;

Seems like some kind of constant folding gone wrong. So I don't think we should merge this until we have a workaround.

I verified that this is working on mac with naga 0.14.1. I didn't try to resolve the merge conflicts myself, just ran the branch. Hopefully those won't be too difficult.

It'll be nice to be on wgpu 0.18, as there are a number of things we want to investigate, including slow shader compilation on D3D12.