wasmtime-wizer: make rayon optional (#12313)

* wasmtime-wizer: make rayon optional

when compiling wasmtime-wizer to wasm32, rayon detects that and tries to
use wasm-bindgen APIs

the new rayon feature flag allows users to choose if snapshotting should
be parallel or sequential

* add the new wasmtime-wizer rayon feature flag to CI micro_checks

Author: Gentle

.github/workflows/main.yml

@@ -431,6 +431,7 @@ jobs:
               -p wasmtime-wizer --no-default-features --features wasmtime
               -p wasmtime-wizer --no-default-features --features wasmprinter
               -p wasmtime-wizer --no-default-features --features component-model
+              -p wasmtime-wizer --no-default-features --features rayon
               -p wasmtime-wizer --no-default-features --all-features
     runs-on: ubuntu-latest
     steps:

crates/wizer/Cargo.toml

@@ -26,7 +26,7 @@ harness = false
 
 [dependencies]
 log = { workspace = true }
-rayon = { workspace = true }
+rayon = { workspace = true, optional = true }
 clap = { workspace = true, optional = true }
 wasm-encoder = { workspace = true, features = ['wasmparser'] }
 wasmparser = { workspace = true, features = ['validate', 'features'] }
@@ -43,6 +43,10 @@ wasmtime-wasi = { workspace = true, features = ["p1"] }
 tokio = { workspace = true, features = ['macros'] }
 
 [features]
+default = ["rayon"]
+# Enables parallel snapshotting.
+# Needs to be disabled if compiling wizer to single-threaded targets like wasm32-unknown-unknown
+rayon = ["dep:rayon"]
 # Enable this dependency to get messages with WAT disassemblies when certain
 # internal panics occur.
 wasmprinter = ['dep:wasmprinter']

crates/wizer/src/lib.rs

@@ -19,6 +19,8 @@ pub use wasmtime::*;
 mod component;
 #[cfg(feature = "component-model")]
 pub use component::*;
+#[cfg(not(feature = "rayon"))]
+mod rayoff;
 
 pub use crate::info::ModuleContext;
 pub use crate::snapshot::SnapshotVal;

crates/wizer/src/rayoff.rs

@@ -0,0 +1,36 @@
+use std::ops::Range;
+
+pub trait ParallelIterator: Iterator {}
+
+impl<T: Iterator> ParallelIterator for T {}
+
+pub trait IntoParallelIterator {
+    type Item;
+    type Iter: Iterator<Item = Self::Item> + ParallelIterator;
+
+    fn into_par_iter(self) -> Self::Iter;
+}
+
+impl IntoParallelIterator for Range<usize> {
+    type Item = usize;
+    type Iter = Range<usize>;
+
+    fn into_par_iter(self) -> Self::Iter {
+        self
+    }
+}
+
+pub trait ParallelExtend<T> {
+    fn par_extend<I>(&mut self, par_iter: I)
+    where
+        I: IntoIterator<Item = T>;
+}
+
+impl<T> ParallelExtend<T> for Vec<T> {
+    fn par_extend<I>(&mut self, par_iter: I)
+    where
+        I: IntoIterator<Item = T>,
+    {
+        self.extend(par_iter);
+    }
+}

crates/wizer/src/snapshot.rs

@@ -1,5 +1,8 @@
 use crate::InstanceState;
 use crate::info::ModuleContext;
+#[cfg(not(feature = "rayon"))]
+use crate::rayoff::{IntoParallelIterator, ParallelExtend};
+#[cfg(feature = "rayon")]
 use rayon::iter::{IntoParallelIterator, ParallelExtend, ParallelIterator};
 use std::convert::TryFrom;
 use std::ops::Range;