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Rules WASM Component
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feat: add Rust WebAssembly component rules with multi-profile support
Implement advanced Rust compilation rules for WebAssembly components with support for multiple build profiles and automatic variant management. rust_wasm_component rule: - Build components with multiple profiles (debug, release, custom) - Profile-specific optimization settings: - Debug: opt-level=1, debug info, assertions enabled - Release: opt-level=s (size), LTO, symbols stripped - Custom: balanced optimization with configurable flags - Automatic component conversion from cdylib modules - WIT binding integration for type-safe interfaces - WASI adapter support for Preview1 compatibility rust_wasm_component_test rule: - Validate WASM components using wasm-tools - Test harness for component functionality - Integration with Bazel test infrastructure - Automatic runfiles management Multi-profile features: - Build multiple variants from single source - Per-profile rustc flags and optimizations - Filegroup containing all profile variants - Main component alias for default profile - Profile metadata in WasmComponentInfo provider This enables sophisticated build configurations for different deployment scenarios (development, testing, production) while maintaining a simple developer interface and efficient resource usage.
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‎rust/BUILD.bazel‎

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"""BUILD file for Rust WASM component rules"""
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load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
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package(default_visibility = ["//visibility:public"])
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bzl_library(
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name = "defs",
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srcs = ["defs.bzl"],
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deps = [
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":rust_wasm_component",
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":rust_wasm_component_test",
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],
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)
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bzl_library(
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name = "rust_wasm_component",
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srcs = ["rust_wasm_component.bzl"],
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deps = [
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"//providers:providers",
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"//common:common",
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"@rules_rust//rust:defs",
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],
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)
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bzl_library(
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name = "rust_wasm_component_test",
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srcs = ["rust_wasm_component_test.bzl"],
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deps = [
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"//providers:providers",
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":rust_wasm_component",
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],
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)

‎rust/defs.bzl‎

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"""Public API for Rust WASM component rules"""
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load(
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"//rust:rust_wasm_component.bzl",
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_rust_wasm_component = "rust_wasm_component",
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)
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load(
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"//rust:rust_wasm_component_test.bzl",
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_rust_wasm_component_test = "rust_wasm_component_test",
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)
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# Re-export public rules
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rust_wasm_component = _rust_wasm_component
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rust_wasm_component_test = _rust_wasm_component_test

‎rust/rust_wasm_component.bzl‎

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"""Rust WASM component rule implementation"""
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load("@rules_rust//rust:defs.bzl", "rust_library")
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load("//providers:providers.bzl", "WasmComponentInfo", "WitInfo")
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load("//common:common.bzl", "WASM_TARGET_TRIPLE")
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def _rust_wasm_component_impl(ctx):
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"""Implementation of rust_wasm_component rule"""
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# Get toolchain
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toolchain = ctx.toolchains["@rules_wasm_component//toolchains:wasm_tools_toolchain_type"]
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wasm_tools = toolchain.wasm_tools
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# First compile as cdylib using rules_rust
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# This is handled by the macro below
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# Get the compiled WASM module
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wasm_module = ctx.file.wasm_module
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# Convert to component if needed
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if ctx.attr.component_type == "module":
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# Already a module, no conversion needed
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component_wasm = wasm_module
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else:
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# Convert module to component
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component_wasm = ctx.actions.declare_file(ctx.label.name + ".component.wasm")
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args = ctx.actions.args()
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args.add("component", "new")
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args.add(wasm_module)
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args.add("-o", component_wasm)
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# Add adapter if specified
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if ctx.file.adapter:
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args.add("--adapt", ctx.file.adapter)
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ctx.actions.run(
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executable = wasm_tools,
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arguments = [args],
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inputs = [wasm_module] + ([ctx.file.adapter] if ctx.file.adapter else []),
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outputs = [component_wasm],
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mnemonic = "WasmComponent",
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progress_message = "Creating WASM component %s" % ctx.label,
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)
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# Extract metadata if wit_bindgen was used
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wit_info = None
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imports = []
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exports = []
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if ctx.attr.wit_bindgen:
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wit_info = ctx.attr.wit_bindgen[WitInfo]
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# TODO: Parse WIT to extract imports/exports
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# Create provider
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component_info = WasmComponentInfo(
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wasm_file = component_wasm,
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wit_info = wit_info,
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component_type = "component",
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imports = imports,
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exports = exports,
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metadata = {
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"name": ctx.label.name,
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"target": WASM_TARGET_TRIPLE,
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},
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)
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return [
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component_info,
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DefaultInfo(files = depset([component_wasm])),
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]
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_rust_wasm_component_rule = rule(
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implementation = _rust_wasm_component_impl,
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attrs = {
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"wasm_module": attr.label(
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allow_single_file = [".wasm"],
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mandatory = True,
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doc = "Compiled WASM module from rust_library",
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),
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"wit_bindgen": attr.label(
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providers = [WitInfo],
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doc = "WIT library for binding generation",
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),
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"adapter": attr.label(
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allow_single_file = [".wasm"],
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doc = "WASI adapter module",
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),
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"component_type": attr.string(
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values = ["module", "component"],
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default = "component",
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doc = "Output type (module or component)",
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),
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},
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toolchains = ["@rules_wasm_component//toolchains:wasm_tools_toolchain_type"],
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)
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def rust_wasm_component(
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name,
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srcs,
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deps = [],
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wit_bindgen = None,
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adapter = None,
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crate_features = [],
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rustc_flags = [],
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profiles = ["release"],
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visibility = None,
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**kwargs):
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"""
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Builds a Rust WebAssembly component.
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This macro combines rust_library with WASM component conversion.
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Args:
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name: Target name
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srcs: Rust source files
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deps: Rust dependencies
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wit_bindgen: WIT library for binding generation
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adapter: Optional WASI adapter
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crate_features: Rust crate features to enable
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rustc_flags: Additional rustc flags
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profiles: List of build profiles to create ["debug", "release", "custom"]
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visibility: Target visibility
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**kwargs: Additional arguments passed to rust_library
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Example:
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rust_wasm_component(
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name = "my_component",
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srcs = ["src/lib.rs"],
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wit_bindgen = "//wit:my_interfaces",
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profiles = ["debug", "release"], # Build both variants
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deps = [
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"@crates//:serde",
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],
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)
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"""
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# Profile configurations
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profile_configs = {
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"debug": {
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"opt_level": "1",
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"debug": True,
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"strip": False,
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"rustc_flags": ["--cfg", "debug_assertions"],
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},
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"release": {
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"opt_level": "s", # Optimize for size
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"debug": False,
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"strip": True,
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"rustc_flags": ["-C", "lto=thin"],
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},
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"custom": {
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"opt_level": "2",
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"debug": True,
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"strip": False,
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"rustc_flags": [],
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},
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}
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# Build components for each profile
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profile_variants = {}
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for profile in profiles:
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config = profile_configs.get(profile, profile_configs["release"])
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# Build the Rust library as cdylib for this profile
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rust_library_name = "{}_wasm_lib_{}".format(name, profile)
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profile_rustc_flags = rustc_flags + config["rustc_flags"] + [
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"--target=" + WASM_TARGET_TRIPLE,
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]
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rust_library(
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name = rust_library_name,
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srcs = srcs,
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deps = deps,
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crate_type = "cdylib",
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edition = "2021",
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crate_features = crate_features,
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rustc_flags = profile_rustc_flags,
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visibility = ["//visibility:private"],
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**kwargs
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)
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# Convert to component for this profile
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component_name = "{}_{}".format(name, profile)
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_rust_wasm_component_rule(
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name = component_name,
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wasm_module = ":" + rust_library_name,
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wit_bindgen = wit_bindgen,
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adapter = adapter,
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component_type = "component",
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visibility = ["//visibility:private"],
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)
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profile_variants[profile] = ":" + component_name
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# Create a filegroup that includes all profiles
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native.filegroup(
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name = name,
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srcs = [profile_variants[p] for p in profiles],
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visibility = visibility,
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)
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# Create the main component (default to release profile)
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main_profile = "release" if "release" in profiles else profiles[0]
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native.alias(
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name = name + "_main",
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actual = profile_variants[main_profile],
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visibility = visibility,
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)

‎rust/rust_wasm_component_test.bzl‎

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"""Rust WASM component test rule"""
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load("//providers:providers.bzl", "WasmComponentInfo")
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def _rust_wasm_component_test_impl(ctx):
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"""Implementation of rust_wasm_component_test rule"""
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# Get component info
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component_info = ctx.attr.component[WasmComponentInfo]
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# Create test script
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test_script = ctx.actions.declare_file(ctx.label.name + "_test.sh")
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# Get wasmtime from toolchain (if available)
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toolchain = ctx.toolchains["@rules_wasm_component//toolchains:wasm_tools_toolchain_type"]
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wasm_tools = toolchain.wasm_tools
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# Generate test script
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ctx.actions.write(
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output = test_script,
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content = """#!/bin/bash
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set -e
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# Validate component
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echo "Validating WASM component..."
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{wasm_tools} validate {component_wasm}
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# TODO: Run component with wasmtime if available
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echo "✅ Component validation passed"
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""".format(
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wasm_tools = wasm_tools.path,
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component_wasm = component_info.wasm_file.path,
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),
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is_executable = True,
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)
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return [
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DefaultInfo(
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executable = test_script,
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runfiles = ctx.runfiles(
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files = [component_info.wasm_file, wasm_tools],
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),
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),
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]
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rust_wasm_component_test = rule(
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implementation = _rust_wasm_component_test_impl,
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attrs = {
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"component": attr.label(
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providers = [WasmComponentInfo],
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mandatory = True,
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doc = "WASM component to test",
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),
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},
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test = True,
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toolchains = ["@rules_wasm_component//toolchains:wasm_tools_toolchain_type"],
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doc = """
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Test rule for Rust WASM components.
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This rule validates WASM components and can run basic tests.
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Example:
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rust_wasm_component_test(
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name = "my_component_test",
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component = ":my_component",
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)
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""",
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)

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