Reduce repo MSRV from 1.85 to 1.84 (#7425)

* Reduce repo MSRV from 1.85 to 1.84

Fixes #7409

* Replace usage of task::Waker::noop()

* Gate waker code to `noop` feature

* Remove unused copied waker function

* Remove doctest from copied code

Author: LegNeato

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ env:
   CI_BINARY_BUILD: "build20"
 
   # This is the MSRV used by `wgpu` itself and all surrounding infrastructure.
-  REPO_MSRV: "1.85"
+  REPO_MSRV: "1.84"
   # This is the MSRV used by the `wgpu-core`, `wgpu-hal`, and `wgpu-types` crates,
   # to ensure that they can be used with firefox.
   CORE_MSRV: "1.82.0"

.github/workflows/docs.yml

@@ -10,7 +10,7 @@ on:
 
 env:
   # This is the MSRV used by `wgpu` itself and all surrounding infrastructure.
-  REPO_MSRV: "1.85"
+  REPO_MSRV: "1.84"
 
   CARGO_INCREMENTAL: false
   CARGO_TERM_COLOR: always

.github/workflows/generate.yml

@@ -13,7 +13,7 @@ env:
   #
 
   # This is the MSRV used by `wgpu` itself and all surrounding infrastructure.
-  REPO_MSRV: "1.85"
+  REPO_MSRV: "1.84"
   RUSTFLAGS: -D warnings
 
 jobs:

Cargo.toml

@@ -50,7 +50,7 @@ ref_as_ptr = "warn"
 
 [workspace.package]
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.84"
 keywords = ["graphics"]
 license = "MIT OR Apache-2.0"
 homepage = "https://wgpu.rs/"

README.md

@@ -149,7 +149,7 @@ On Linux, you can point to them using `LD_LIBRARY_PATH` environment.
 Due to complex dependants, we have two MSRV policies:
 
 - `naga`, `wgpu-core`, `wgpu-hal`, and `wgpu-types`'s MSRV is **1.76**.
-- The rest of the workspace has an MSRV of **1.85**.
+- The rest of the workspace has an MSRV of **1.84**.
 
 It is enforced on CI (in "/.github/workflows/ci.yml") with the `CORE_MSRV` and `REPO_MSRV` variables.
 This version can only be upgraded in breaking releases, though we release a breaking version every three months.

examples/standalone/01_hello_compute/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "wgpu-example-01-hello-compute"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.84"
 publish = false
 
 [dependencies]

examples/standalone/02_hello_window/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "wgpu-example-02-hello-window"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.84"
 publish = false
 
 [dependencies]

examples/standalone/custom_backend/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "wgpu-example-custom-backend"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.84"
 publish = false
 
 [dependencies]

naga/xtask/Cargo.toml

@@ -3,7 +3,7 @@ name = "xtask"
 version = "0.1.0"
 edition = "2021"
 publish = false
-rust-version = "1.85"
+rust-version = "1.84"
 
 [dependencies]
 anyhow = "1"

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "1.85"
+channel = "1.84"
 components = ["rustfmt", "clippy"]
 targets = ["wasm32-unknown-unknown"]

wgpu/src/api/device.rs

@@ -51,7 +51,7 @@ impl Device {
         use core::future::Future as _;
         use core::pin::pin;
         use core::task;
-        let ctx = &mut task::Context::from_waker(task::Waker::noop());
+        let ctx = &mut task::Context::from_waker(waker::noop_waker_ref());
 
         let instance = Instance::new(&InstanceDescriptor {
             backends: Backends::NOOP,
@@ -695,3 +695,36 @@ impl fmt::Display for Error {
         }
     }
 }
+
+// Copied from [`futures::task::noop_waker`].
+// Needed until MSRV is 1.85 with `task::Waker::noop()` available
+#[cfg(feature = "noop")]
+mod waker {
+    use core::ptr::null;
+    use core::task::{RawWaker, RawWakerVTable, Waker};
+
+    unsafe fn noop_clone(_data: *const ()) -> RawWaker {
+        noop_raw_waker()
+    }
+
+    unsafe fn noop(_data: *const ()) {}
+
+    const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+    const fn noop_raw_waker() -> RawWaker {
+        RawWaker::new(null(), &NOOP_WAKER_VTABLE)
+    }
+
+    /// Get a static reference to a [`Waker`] which
+    /// does nothing when `wake()` is called on it.
+    #[inline]
+    pub fn noop_waker_ref() -> &'static Waker {
+        struct SyncRawWaker(RawWaker);
+        unsafe impl Sync for SyncRawWaker {}
+
+        static NOOP_WAKER_INSTANCE: SyncRawWaker = SyncRawWaker(noop_raw_waker());
+
+        // SAFETY: `Waker` is #[repr(transparent)] over its `RawWaker`.
+        unsafe { &*(&NOOP_WAKER_INSTANCE.0 as *const RawWaker as *const Waker) }
+    }
+}

xtask/Cargo.toml

@@ -2,7 +2,7 @@
 name = "xtask"
 version = "0.1.0"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.84"
 publish = false
 
 [lints.rust]