fix(core): use BufferMapState::Active for any BufferUsages::MAP_* flags

For cases where a buffer is `mapped_at_creation`, our current
implementation of `Buffer::create` initializes the buffer's internal
state with `BufferMapState::Init` (which contains a staging buffer
underneath the hood) for a descriptor requesting `MAP_READ` that is
copied to a host-backed buffer . `MAP_WRITE` works a little differently,
starting from the beginning with a host-backed buffer.

`Init` does a buffer copy between the staging buffer and the host-backed
buffer in the device's queue when the buffer is `unmap`ped. However,
`Buffer::map_async` (correctly) assumes that a host-backed buffer need
not wait for anything in the queue. This results in a bug where
`map_async` doesn't actually wait long enough for the device queue to
complete its operations before resolving. Oops!

Up to the point where a buffer is unmapped after being mapped at
creation, `MAP_READ`, `MAP_WRITE`, and even _non_-`MAP_*` buffers'
capabilities are the same. That is, we should be able to get mutable
slices for mapped ranges, no matter what. So, make `MAP_READ` just
initialize its internal state in the same way as with `MAP_WRITE`.

Author: ErichDonGubler

cts_runner/test.lst

@@ -4,7 +4,7 @@
 // ```
 unittests:*
 webgpu:api,operation,buffers,createBindGroup:buffer_binding_resource:*
-fails-if(vulkan,dx12,metal): webgpu:api,operation,buffers,map:mapAsync,read:*
+webgpu:api,operation,buffers,map:mapAsync,read:*
 webgpu:api,operation,command_buffer,basic:*
 webgpu:api,operation,command_buffer,copyBufferToBuffer:*
 fails-if(vulkan) webgpu:api,operation,command_buffer,copyTextureToTexture:copy_depth_stencil:format="depth24plus"

wgpu-core/src/device/resource.rs

@@ -990,7 +990,10 @@ impl Device {
 
         let buffer_use = if !desc.mapped_at_creation {
             wgt::BufferUses::empty()
-        } else if desc.usage.contains(wgt::BufferUsages::MAP_WRITE) {
+        } else if desc
+            .usage
+            .intersects(wgt::BufferUsages::MAP_WRITE | wgt::BufferUsages::MAP_READ)
+        {
             // buffer is mappable, so we are just doing that at start
             let map_size = buffer.size;
             let mapping = if map_size == 0 {