Fix missing target features when using xforms

Author: daxpedda

Diff for: CHANGELOG.md

@@ -45,9 +45,12 @@
 * Fix MSRV compilation.
   [#3927](https://github.com/rustwasm/wasm-bindgen/pull/3927)
 
-* Fixed `clippy::empty_docs` lint.
+* Fix `clippy::empty_docs` lint.
   [#3946](https://github.com/rustwasm/wasm-bindgen/pull/3946)
 
+* Fix missing target features in module when enabling reference types or multi-value transformation.
+  [#3967](https://github.com/rustwasm/wasm-bindgen/pull/3967)
+
 --------------------------------------------------------------------------------
 
 ## [0.2.92](https://github.com/rustwasm/wasm-bindgen/compare/0.2.91...0.2.92)

Diff for: crates/externref-xform/Cargo.toml

@@ -15,6 +15,7 @@ rust-version = "1.57"
 [dependencies]
 anyhow = "1.0"
 walrus = "0.20.2"
+wasm-bindgen-wasm-conventions = { path = "../wasm-conventions", version = "=0.2.92" }
 
 [dev-dependencies]
 rayon = "1.0"

Diff for: crates/externref-xform/src/lib.rs

@@ -101,6 +101,9 @@ impl Context {
     /// large the function table is so we know what indexes to hand out when
     /// we're appending entries.
     pub fn prepare(&mut self, module: &mut Module) -> Result<(), Error> {
+        // Insert reference types to the target features section.
+        wasm_bindgen_wasm_conventions::insert_target_feature(module, "reference-types");
+
         // Figure out what the maximum index of functions pointers are. We'll
         // be adding new entries to the function table later (maybe) so
         // precalculate this ahead of time.

Diff for: crates/multi-value-xform/Cargo.toml

@@ -15,6 +15,7 @@ rust-version = "1.57"
 [dependencies]
 anyhow = "1.0"
 walrus = "0.20.2"
+wasm-bindgen-wasm-conventions = { path = "../wasm-conventions", version = "=0.2.92" }
 
 [dev-dependencies]
 rayon = "1.0"

Diff for: crates/multi-value-xform/src/lib.rs

@@ -117,6 +117,9 @@ pub fn run(
     shadow_stack_pointer: walrus::GlobalId,
     to_xform: &[(walrus::FunctionId, usize, Vec<walrus::ValType>)],
 ) -> Result<Vec<walrus::FunctionId>, anyhow::Error> {
+    // Insert multi-value to the target features section.
+    wasm_bindgen_wasm_conventions::insert_target_feature(module, "multivalue");
+
     let mut wrappers = Vec::new();
     for (func, return_pointer_index, results) in to_xform {
         wrappers.push(xform_one(

Diff for: crates/wasm-conventions/src/lib.rs

@@ -6,10 +6,12 @@
 //! * The shadow stack pointer
 //! * The canonical linear memory that contains the shadow stack
 
+use std::cmp::Ordering;
+
 use anyhow::{anyhow, bail, Result};
 use walrus::{
     ir::Value, ElementId, FunctionBuilder, FunctionId, FunctionKind, GlobalId, GlobalKind,
-    InitExpr, MemoryId, Module, ValType,
+    InitExpr, MemoryId, Module, RawCustomSection, ValType,
 };
 
 /// Get a Wasm module's canonical linear memory.
@@ -148,3 +150,45 @@ pub fn get_or_insert_start_builder(module: &mut Module) -> &mut FunctionBuilder
         .unwrap_local_mut()
         .builder_mut()
 }
+
+pub fn insert_target_feature(module: &mut Module, new_feature: &str) {
+    // Insert reference types to the target features section.
+    let (_, section) = module
+        .customs
+        .iter_mut()
+        .find(|(_, custom)| custom.name() == "target_features")
+        .expect("`target_features` section could not be found");
+    let section: &mut RawCustomSection = section.as_any_mut().downcast_mut().unwrap();
+
+    // Try to find if the target feature is already present.
+    let mut bytes = section.data[1..].iter();
+
+    // The first byte contains the target feature count.
+    for _ in 0..section.data[0] {
+        // Skip the prefix.
+        bytes.next().unwrap();
+        // Read the length of the target feature.
+        let length = *bytes.next().unwrap();
+        // Read the feature.
+        let mut feature = bytes.by_ref().take(length.into());
+
+        // If we found the target feature, we are done here.
+        if let Ordering::Equal = feature.by_ref().cmp(new_feature.as_bytes()) {
+            return;
+        }
+
+        // If we couldn't find it, consume it so we can advance.
+        feature.for_each(|_| ());
+    }
+
+    // If we couldn't find the target feature, insert it.
+
+    // The first byte contains the target feature count, which we increase by one.
+    section.data[0] += 1;
+    // Then we insert the "enabled" prefix at the end.
+    section.data.push(b'+');
+    // The next byte contains the length of the target feature string.
+    section.data.push(new_feature.len() as u8);
+    // Lastly the target feature string is inserted.
+    section.data.extend(new_feature.as_bytes());
+}