Wasmtime toplevel module: re-export wasmparser.

crates/wasmtime/Cargo.toml

@@ -278,3 +278,19 @@ call-hook = []
 # Enables support for "memory protection keys" which can be used in conjunction
 # with the pooling allocator on x64 to compact linear memory allocations.
 memory-protection-keys = ["pooling-allocator"]
+
+# Enables a re-export of wasmparser, so that an embedder of Wasmtime can use
+# exactly the version of the parser library that Wasmtime does. Sometimes this
+# is necessary, e.g. to guarantee that there will not be any mismatches in
+# which modules are accepted due to Wasm feature configuration or support
+# levels.
+#
+# Note that when this feature is enabled, the version of wasmparser that is
+# re-exported is *not subject to semver*: we reserve the right to make patch
+# releases of Wasmtime that bump the version of wasmparser used, and hence the
+# version re-exported, in semver-incompatible ways. This is the tradeoff that
+# the embedder needs to opt into: in order to stay exactly in sync with an
+# internal detail of Wasmtime, the cost is visibility into potential internal
+# version changes. This is why the re-export is guarded by a feature flag which
+# is off by default.
+reexport-wasmparser = []

crates/wasmtime/src/lib.rs

@@ -393,6 +393,24 @@ use sync_nostd as sync;
 #[doc(no_inline)]
 pub use anyhow::{Error, Result};
 
+/// A re-exported instance of Wasmtime's `wasmparser` dependency.
+///
+/// This may be useful for embedders that also use `wasmparser`
+/// directly: it allows embedders to ensure that they are using the same
+/// version as Wasmtime, both to eliminate redundant dependencies on
+/// multiple versions of the library, and to ensure compatibility in
+/// validation and feature support.
+///
+/// Note that this re-export is *not subject to semver*: we reserve the
+/// right to make patch releases of Wasmtime that bump the version of
+/// wasmparser used, and hence the version re-exported, in
+/// semver-incompatible ways. This is the tradeoff that the embedder
+/// needs to opt into: in order to stay exactly in sync with an internal
+/// detail of Wasmtime, the cost is visibility into potential internal
+/// version changes.
+#[cfg(feature = "reexport-wasmparser")]
+pub use wasmparser;
+
 fn _assert_send_and_sync<T: Send + Sync>() {}
 
 fn _assertions_lib() {