Fix bug where mapped range in WebBuffer is not cloned correctly (#8349)

Co-authored-by: Ryan Kaplan <ryan@Ryans-M2>

CHANGELOG.md

@@ -80,6 +80,8 @@ SamplerDescriptor {
 
 ### Bug Fixes
 
+- Fixed bug where mapping sub-ranges of a buffer on web would fail with `OperationError: GPUBuffer.getMappedRange: GetMappedRange range extends beyond buffer's mapped range`. By @ryankaplan in [#8349](https://github.com/gfx-rs/wgpu/pull/8349)
+
 #### General
 
 - Reject fragment shader output `location`s > `max_color_attachments` limit. By @ErichDonGubler in [#8316](https://github.com/gfx-rs/wgpu/pull/8316).

wgpu/src/api/buffer.rs

@@ -688,6 +688,10 @@ fn range_overlaps(a: &Range<BufferAddress>, b: &Range<BufferAddress>) -> bool {
     a.start < b.end && b.start < a.end
 }
 
+fn range_contains(a: &Range<BufferAddress>, b: &Range<BufferAddress>) -> bool {
+    a.start <= b.start && a.end >= b.end
+}
+
 #[derive(Debug, Copy, Clone)]
 enum RangeMappingKind {
     Mutable,
@@ -786,7 +790,7 @@ impl MapContext {
         if self.mapped_range.is_empty() {
             panic!("tried to call get_mapped_range(_mut) on an unmapped buffer");
         }
-        if !range_overlaps(&self.mapped_range, &new_sub.index) {
+        if !range_contains(&self.mapped_range, &new_sub.index) {
             panic!(
                 "tried to call get_mapped_range(_mut) on a range that is not entirely mapped. \
                  Attempted to get range {}, but the mapped range is {}..{}",

wgpu/src/backend/webgpu.rs

@@ -1221,7 +1221,7 @@ pub struct WebBuffer {
     /// The associated GPU buffer.
     inner: webgpu_sys::GpuBuffer,
     /// The mapped array buffer and mapped range.
-    mapping: RefCell<WebBufferMapState>,
+    mapping: Rc<RefCell<WebBufferMapState>>,
     /// Unique identifier for this Buffer.
     ident: crate::cmp::Identifier,
 }
@@ -1231,10 +1231,10 @@ impl WebBuffer {
     fn new(inner: webgpu_sys::GpuBuffer, desc: &crate::BufferDescriptor<'_>) -> Self {
         Self {
             inner,
-            mapping: RefCell::new(WebBufferMapState {
+            mapping: Rc::new(RefCell::new(WebBufferMapState {
                 mapped_buffer: None,
                 range: 0..desc.size,
-            }),
+            })),
             ident: crate::cmp::Identifier::create(),
         }
     }