[types] Replace conditional derive(thiserror::Error) with unconditional impl. (#8384)

CHANGELOG.md

@@ -88,6 +88,7 @@ SamplerDescriptor {
 - WebGPU device requests now support the required limits `maxColorAttachments` and `maxColorAttachmentBytesPerSample`. By @evilpie in [#8328](https://github.com/gfx-rs/wgpu/pull/8328)
 - Reject binding indices that exceed `wgpu_types::Limits::max_bindings_per_bind_group` when deriving a bind group layout for a pipeline. By @jimblandy in [#8325](https://github.com/gfx-rs/wgpu/pull/8325).
 - Removed three features from `wgpu-hal` which did nothing useful: `"cargo-clippy"`, `"gpu-allocator"`, and `"rustc-hash"`. By @kpreid in [#8357](https://github.com/gfx-rs/wgpu/pull/8357).
+- `wgpu_types::PollError` now always implements the `Error` trait. By @kpreid in [#8384](https://github.com/gfx-rs/wgpu/pull/8384).
 
 #### DX12
 

Cargo.lock

@@ -5053,7 +5053,6 @@ dependencies = [
  "log",
  "serde",
  "serde_json",
- "thiserror 2.0.17",
  "web-sys",
 ]
 

wgpu-types/Cargo.toml

@@ -37,7 +37,7 @@ alloc_instead_of_core = "warn"
 
 [features]
 default = ["std"]
-std = ["js-sys?/std", "web-sys?/std", "thiserror/std"]
+std = ["js-sys?/std", "web-sys?/std"]
 strict_asserts = []
 fragile-send-sync-non-atomic-wasm = []
 serde = ["dep:serde", "bitflags/serde"]
@@ -52,7 +52,6 @@ web = ["dep:js-sys", "dep:web-sys"]
 bitflags.workspace = true
 bytemuck = { workspace = true, features = ["derive"] }
 log.workspace = true
-thiserror = { workspace = true, optional = true }
 serde = { workspace = true, default-features = false, features = [
     "alloc",
     "derive",

wgpu-types/src/lib.rs

@@ -4564,24 +4564,35 @@ impl<T> PollType<T> {
     }
 }
 
-/// Error states after a device poll
+/// Error states after a device poll.
 #[derive(Debug)]
-#[cfg_attr(feature = "std", derive(thiserror::Error))]
 pub enum PollError {
     /// The requested Wait timed out before the submission was completed.
-    #[cfg_attr(
-        feature = "std",
-        error("The requested Wait timed out before the submission was completed.")
-    )]
     Timeout,
     /// The requested Wait was given a wrong submission index.
-    #[cfg_attr(
-        feature = "std",
-        error("Tried to wait using a submission index ({0}) that has not been returned by a successful submission (last successful submission: {1})")
-    )]
     WrongSubmissionIndex(u64, u64),
 }
 
+// This impl could be derived by `thiserror`, but by not doing so, we can reduce the number of
+// dependencies this early in the dependency graph, which may improve build parallelism.
+impl fmt::Display for PollError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            PollError::Timeout => {
+                f.write_str("The requested Wait timed out before the submission was completed.")
+            }
+            PollError::WrongSubmissionIndex(requested, successful) => write!(
+                f,
+                "Tried to wait using a submission index ({requested}) \
+                that has not been returned by a successful submission \
+                (last successful submission: {successful}"
+            ),
+        }
+    }
+}
+
+impl core::error::Error for PollError {}
+
 /// Status of device poll operation.
 #[derive(Debug, PartialEq, Eq)]
 pub enum PollStatus {