simplify the protocol to reduce the diff and code size

Author: lukesandberg

turbopack/crates/turbopack-ecmascript-runtime/js/src/shared/runtime-utils.ts

@@ -95,10 +95,8 @@ function createModuleObject(id: ModuleId): Module {
   }
 }
 
-type BindingTag = 0 | 1 | 2
-const BindingTag_Getter = 0 as BindingTag
-const BindingTag_GetterSetter = 1 as BindingTag
-const BindingTag_Value = 2 as BindingTag
+type BindingTag = 0
+const BindingTag_Value = 0 as BindingTag
 
 // an arbitrary sequence of bindings as
 // - a prop name
@@ -117,30 +115,32 @@ function esm(exports: Exports, bindings: EsmBindings) {
   let i = 0
   while (i < bindings.length) {
     const propName = bindings[i++] as string
-    const tag = bindings[i++] as BindingTag
-    switch (tag) {
-      case BindingTag_Getter:
+    const tagOrFunction = bindings[i++]
+    if (typeof tagOrFunction === 'number') {
+      if (tagOrFunction === BindingTag_Value) {
         defineProp(exports, propName, {
-          get: bindings[i++] as () => unknown,
+          value: bindings[i++],
           enumerable: true,
+          writable: false,
         })
-        break
-      case BindingTag_GetterSetter:
+      } else {
+        throw new Error(`unexpected tag: ${tagOrFunction}`)
+      }
+    } else {
+      const getterFn = tagOrFunction as () => unknown
+      if (typeof bindings[i] === 'function') {
+        const setterFn = bindings[i++] as (v: unknown) => void
         defineProp(exports, propName, {
-          get: bindings[i++] as () => unknown,
-          set: bindings[i++] as (v: unknown) => void,
+          get: getterFn,
+          set: setterFn,
           enumerable: true,
         })
-        break
-      case BindingTag_Value:
+      } else {
         defineProp(exports, propName, {
-          value: bindings[i++],
+          get: getterFn,
           enumerable: true,
-          writable: false,
         })
-        break
-      default:
-        throw new Error(`unexpected tag: ${tag}`)
+      }
     }
   }
   Object.seal(exports)
@@ -287,9 +287,9 @@ function interopEsm(
     current = getProto(current)
   ) {
     for (const key of Object.getOwnPropertyNames(current)) {
-      bindings.push(key, BindingTag_Getter, createGetter(raw, key))
+      bindings.push(key, createGetter(raw, key))
       if (defaultLocation === -1 && key === 'default') {
-        defaultLocation = bindings.length - 2 // point at the tag
+        defaultLocation = bindings.length - 1
       }
     }
   }
@@ -299,8 +299,8 @@ function interopEsm(
   if (!(allowExportDefault && defaultLocation >= 0)) {
     // Replace the binding with one for the namespace itself in order to preserve iteration order.
     if (defaultLocation >= 0) {
-      bindings[defaultLocation] = BindingTag_Value
-      bindings[defaultLocation + 1] = raw
+      // Replace the getter with the value
+      bindings.splice(defaultLocation, 1, BindingTag_Value, raw)
     } else {
       bindings.push('default', BindingTag_Value, raw)
     }

turbopack/crates/turbopack-ecmascript/src/references/esm/export.rs

@@ -709,6 +709,9 @@ impl EsmExports {
                         .map(|ident| {
                             let expr = ident.as_expr_individual(DUMMY_SP);
                             let read_expr = expr.map_either(Expr::from, Expr::from).into_inner();
+                            // For imported bindings we could simply export the'import' and have the runtime hook the bindings together.
+                            // This would be cute, slightly smaller codegen but efficiency is an open question.  In fact we could even
+                            // perform the 'liveness' check at runtime by querying the property descriptor.
                             match (liveness, export_usage_info.is_circuit_breaker) {
                                 (Liveness::Constant, false) => ExportBinding::Value(quote!(
                                 "$expr" as Expr, expr: Expr = read_expr
@@ -769,16 +772,14 @@ impl EsmExports {
                 ));
                 match exprs {
                     ExportBinding::Getter(getter) => {
-                        getters.push(Some(Expr::Lit(Lit::Num(Number::from(0))).into()));
                         getters.push(Some(getter.into()));
                     }
                     ExportBinding::GetterSetter(getter, setter) => {
-                        getters.push(Some(Expr::Lit(Lit::Num(Number::from(1))).into()));
                         getters.push(Some(getter.into()));
                         getters.push(Some(setter.into()));
                     }
                     ExportBinding::Value(value) => {
-                        getters.push(Some(Expr::Lit(Lit::Num(Number::from(2))).into()));
+                        getters.push(Some(Expr::Lit(Lit::Num(Number::from(0))).into()));
                         getters.push(Some(value.into()));
                     }
                     ExportBinding::None => {}

turbopack/crates/turbopack-ecmascript/src/references/mod.rs

@@ -3367,6 +3367,8 @@ impl VisitAstPath for ModuleReferencesVisitor<'_> {
                     f(ident.sym.as_str().into(), Liveness::Constant);
                 }
                 Decl::Var(var_decl) => {
+                    // TODO: examine whether the value is ever mutated rather than just checking
+                    // 'const'
                     let liveness = match var_decl.kind {
                         VarDeclKind::Var => Liveness::Live,
                         VarDeclKind::Let => Liveness::Live,