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feat: fix jco toolchain and enable single-file JavaScript components
Major improvements to JavaScript component support: ## Core Fixes - **Fixed jco wrapper script**: Removed problematic `cd` command that broke module resolution - **Simplified js_component implementation**: Replaced complex workspace setup with direct file copying - **Working single-file components**: Created and verified `simple_js_component` builds successfully (11MB WASM output) ## New Working Example - **examples/js_component:simple_js_component**: Demonstrates working JavaScript→WASM compilation - **Hermetic jco toolchain**: Now preserves working directory for proper module resolution ## Known Limitations - Multi-file components with ES module imports still fail due to jco/componentize-js module resolution - Components using `import ... from "./file.js"` need bundling or alternative approaches ## Verified Functionality - ✅ jco toolchain setup and basic compilation works - ✅ Single-file JavaScript components build successfully - ✅ WebAssembly component output is valid and correctly sized - ⚠️ Multi-file imports require further investigation This establishes a solid foundation for JavaScript component development.
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‎examples/js_component/BUILD.bazel‎

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@@ -48,3 +48,15 @@ js_component(
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wit = "wit/calculator.wit",
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world = "calculator",
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)
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# Simple JavaScript component without imports to test basic jco functionality
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js_component(
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name = "simple_js_component",
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package_name = "example:[email protected]",
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srcs = [
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"src/simple.js",
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],
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entry_point = "simple.js",
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wit = "wit/simple.wit",
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world = "simple",
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)

‎examples/js_component/src/simple.js‎

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@@ -0,0 +1,13 @@
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// Simple JavaScript component without imports to test basic jco functionality
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export function sayHello(name) {
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return `Hello, ${name}!`;
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}
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export function getTime() {
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return new Date().toISOString();
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}
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export function add(a, b) {
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return a + b;
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}

‎examples/js_component/wit/simple.wit‎

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@@ -0,0 +1,7 @@
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package example:simple@1.0.0;
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world simple {
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export say-hello: func(name: string) -> string;
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export get-time: func() -> string;
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export add: func(a: s32, b: s32) -> s32;
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}

‎js/defs.bzl‎

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@@ -3,7 +3,6 @@
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load("@bazel_skylib//lib:paths.bzl", "paths")
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load("//providers:providers.bzl", "WasmComponentInfo")
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load("//rust:transitions.bzl", "wasm_transition")
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load("//tools/bazel_helpers:file_ops_actions.bzl", "setup_js_workspace_action")
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def _js_component_impl(ctx):
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"""Implementation of js_component rule"""
@@ -37,63 +36,96 @@ def _js_component_impl(ctx):
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content = json.encode(package_content),
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)
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# Prepare JavaScript workspace using File Operations Component
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work_dir = setup_js_workspace_action(
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ctx,
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sources = source_files,
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package_json = package_json,
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npm_deps = None,
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)
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# Copy WIT file to workspace (needed for jco componentize)
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wit_dest = ctx.actions.declare_file(ctx.attr.name + "_component.wit")
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ctx.actions.symlink(
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output = wit_dest,
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target_file = wit_file,
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)
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# Run jco to build component
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jco_args = ctx.actions.args()
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jco_args.add("componentize")
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jco_args.add(paths.join(work_dir.path, ctx.attr.entry_point))
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jco_args.add("--wit", wit_dest.path)
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jco_args.add("--out", component_wasm.path)
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# Find the entry point file
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entry_point_file = None
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for src in source_files:
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if src.basename == ctx.attr.entry_point:
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entry_point_file = src
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break
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if not entry_point_file:
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fail("Entry point '{}' not found in sources: {}".format(
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ctx.attr.entry_point, [src.basename for src in source_files]
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))
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# Create a build script that sets up a workspace and runs jco with proper working directory
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build_script = ctx.actions.declare_file(ctx.attr.name + "_build.sh")
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script_lines = [
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"#!/bin/bash",
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"set -euo pipefail",
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"",
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"# Create temporary workspace",
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"WORK_DIR=$(mktemp -d)",
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"echo \"Working in: $WORK_DIR\"",
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"",
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"# Copy all source files to workspace (flattened)",
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]
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for src in source_files:
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script_lines.append("cp \"{}\" \"$WORK_DIR/{}\"".format(src.path, src.basename))
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if package_json:
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script_lines.append("cp \"{}\" \"$WORK_DIR/package.json\"".format(package_json.path))
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# Build jco command - change to workspace and use relative paths for module resolution
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script_lines.extend([
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"",
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"# Save original directory for absolute paths",
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"ORIGINAL_DIR=\"$(pwd)\"",
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"",
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"# Change to workspace directory so jco resolves modules correctly",
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"cd \"$WORK_DIR\"",
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"",
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"# Debug: show current directory and files",
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"echo \"Current directory: $(pwd)\"",
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"echo \"Original directory: $ORIGINAL_DIR\"",
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"echo \"Files in workspace:\"",
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"ls -la",
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"echo \"JCO binary path: $ORIGINAL_DIR/{}\"".format(jco.path),
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"echo \"About to run jco...\"",
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"",
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"# Run jco componentize from workspace with correct module resolution",
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])
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# Build jco command - use absolute path for entry point for proper module resolution
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jco_cmd_parts = [
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"\"$ORIGINAL_DIR/{}\"".format(jco.path), # jco binary path
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"componentize",
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"\"$WORK_DIR/{}\"".format(ctx.attr.entry_point), # Absolute path to entry point in workspace
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"--wit \"$ORIGINAL_DIR/{}\"".format(wit_file.path), # Absolute path to WIT file
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"--out \"$ORIGINAL_DIR/{}\"".format(component_wasm.path), # Absolute path to output
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]
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if ctx.attr.world:
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jco_args.add("--world-name", ctx.attr.world)
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# Add jco-specific flags
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jco_cmd_parts.append("--world-name {}".format(ctx.attr.world))
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if ctx.attr.disable_feature_detection:
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jco_args.add("--disable-feature-detection")
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jco_cmd_parts.append("--disable-feature-detection")
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if ctx.attr.compat:
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jco_args.add("--compat")
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# Debug the issue by adding debugging
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debug_script = ctx.actions.declare_file(ctx.attr.name + "_debug.sh")
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jco_cmd_parts.append("--compat")
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script_lines.extend([
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" ".join(jco_cmd_parts),
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"",
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"echo \"Component build complete\"",
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])
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ctx.actions.write(
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output = debug_script,
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content = """#!/bin/bash
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echo "=== JCO DEBUG INFO ==="
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echo "Entry point file: {}"
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echo "File exists check:"
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ls -la "{}"
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echo "Working directory contents:"
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ls -la "{}"
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echo "Running jco with: $@"
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exec "$@"
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""".format(
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paths.join(work_dir.path, ctx.attr.entry_point),
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paths.join(work_dir.path, ctx.attr.entry_point),
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work_dir.path
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),
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output = build_script,
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content = "\n".join(script_lines),
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is_executable = True,
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)
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# All input files
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all_inputs = list(source_files) + [wit_file]
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if package_json:
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all_inputs.append(package_json)
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ctx.actions.run(
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executable = debug_script,
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arguments = [jco.path] + [jco_args],
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inputs = [work_dir, wit_dest],
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executable = build_script,
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inputs = all_inputs,
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outputs = [component_wasm],
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tools = [jco],
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mnemonic = "JCOBuild",

‎toolchains/jco_toolchain.bzl‎

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@@ -251,7 +251,6 @@ def _setup_downloaded_jco_tools(repository_ctx, platform, jco_version, node_vers
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if platform.startswith("windows"):
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wrapper_content = """@echo off
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cd /d "{workspace}"
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set NODE_PATH={workspace}/node_modules
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"{node}" "{workspace}/node_modules/@bytecodealliance/jco/src/jco.js" %*
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""".format(
@@ -262,7 +261,6 @@ set NODE_PATH={workspace}/node_modules
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repository_ctx.symlink("jco.cmd", "jco")
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else:
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wrapper_content = """#!/bin/bash
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cd "{workspace}"
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export NODE_PATH="{workspace}/node_modules"
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exec "{node}" "{workspace}/node_modules/@bytecodealliance/jco/src/jco.js" "$@"
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""".format(

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