Deprecate --reference-types (#4237)

Author: daxpedda

CHANGELOG.md

@@ -31,6 +31,9 @@
 * Reference type proposal transformations are not applied by default when detecting it in the Wasm module for the bundler target because currently `webpack` doesn't support it.
   [#4235](https://github.com/rustwasm/wasm-bindgen/pull/4235)
 
+* Deprecate `--reference-types` in favor of automatic target feature detection.
+  [#4237](https://github.com/rustwasm/wasm-bindgen/pull/4237)
+
 ### Fixed
 
 * Fixed methods with `self: &Self` consuming the object.
@@ -57,6 +60,9 @@
 * Fixed invalid TypeScript return types for multivalue signatures.
   [#4210](https://github.com/rustwasm/wasm-bindgen/pull/4210)
 
+* Only emit `table.fill` instructions if the bulk-memory proposal is enabled.
+  [#4237](https://github.com/rustwasm/wasm-bindgen/pull/4237)
+
 --------------------------------------------------------------------------------
 
 ## [0.2.95](https://github.com/rustwasm/wasm-bindgen/compare/0.2.94...0.2.95)

crates/cli/src/bin/wasm-bindgen.rs

@@ -40,7 +40,7 @@ Options:
     --web                        Deprecated, use `--target web`
     --no-modules                 Deprecated, use `--target no-modules`
     --weak-refs                  Deprecated, is runtime-detected
-    --reference-types            Enable usage of WebAssembly reference types
+    --reference-types            Deprecated, use `-Ctarget-feature=+reference-types`
     -V --version                 Print the version number of wasm-bindgen
 
 Additional documentation: https://rustwasm.github.io/wasm-bindgen/reference/cli.html

crates/externref-xform/src/lib.rs

@@ -52,6 +52,9 @@ pub struct Context {
 
     // The externref table we'll be using, injected after construction
     table: Option<TableId>,
+
+    // If the bulk memory proposal is enabled.
+    bulk_memory: bool,
 }
 
 pub struct Meta {
@@ -105,6 +108,11 @@ impl Context {
         wasm_bindgen_wasm_conventions::insert_target_feature(module, "reference-types")
             .context("failed to parse `target_features` custom section")?;
 
+        self.bulk_memory = matches!(
+            wasm_bindgen_wasm_conventions::target_feature(module, "bulk-memory"),
+            Ok(true)
+        );
+
         // 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.
@@ -671,11 +679,23 @@ impl Transform<'_> {
         // that the table doesn't accidentally hold a strong reference to items
         // no longer in use by our Wasm instance.
         if externref_stack > 0 {
+            if self.cx.bulk_memory {
+                body.local_get(fp)
+                    .ref_null(RefType::Externref)
+                    .i32_const(externref_stack)
+                    .table_fill(self.table);
+            } else {
+                for i in 0..externref_stack {
+                    body.local_get(fp);
+                    if i > 0 {
+                        body.i32_const(i).binop(BinaryOp::I32Add);
+                    }
+                    body.ref_null(RefType::Externref);
+                    body.table_set(self.table);
+                }
+            }
+
             body.local_get(fp)
-                .ref_null(RefType::Externref)
-                .i32_const(externref_stack)
-                .table_fill(self.table)
-                .local_get(fp)
                 .i32_const(externref_stack)
                 .binop(BinaryOp::I32Add)
                 .global_set(self.stack_pointer);

crates/externref-xform/tests/anyref-param.wat

@@ -25,8 +25,7 @@
     call $foo
     local.get 1
     ref.null extern
-    i32.const 1
-    table.fill 0
+    table.set 0
     local.get 1
     i32.const 1
     i32.add

crates/externref-xform/tests/mixed-export.wat

@@ -34,8 +34,7 @@
     call $a
     local.get 5
     ref.null extern
-    i32.const 1
-    table.fill 0
+    table.set 0
     local.get 5
     i32.const 1
     i32.add

guide/src/reference/cli.md

@@ -84,14 +84,6 @@ When generating bundler-compatible code (see the section on [deployment]) this
 indicates that the bundled code is always intended to go into a browser so a few
 checks for Node.js can be elided.
 
-### `--reference-types`
-
-Enables usage of the [WebAssembly References Types
-proposal](https://github.com/webassembly/reference-types) proposal, meaning that
-the WebAssembly binary will use `externref` when importing and exporting
-functions that work with `JsValue`. For more information see the [documentation
-about reference types](./reference-types.md).
-
 ### `--omit-default-module-path`
 
 Don't add WebAssembly fallback imports in generated JavaScript.

guide/src/reference/reference-types.md

@@ -42,7 +42,8 @@ export function takes_js_value(a) {
 
 We can see here how under the hood the JS is managing a table of JS values which
 are passed to the Wasm binary, so Wasm actually only works in indices. If we
-pass the `--reference-types` flag to the CLI, however, the generated JS looks like:
+compile with `-Ctarget-feature=+reference-types` (by default since Rust v1.82),
+however, the generated JS looks like:
 
 ```js
 export function takes_js_value(a) {