feat(wasm): wasm_component_import — adopt a prebuilt .wasm component (#489)

examples/component_import_example/BUILD.bazel

@@ -0,0 +1,33 @@
+"""Example: adopt a prebuilt .wasm component, then validate it.
+
+`wasm_component_import` brings an already-built component (fetched release
+asset, vendored artifact, or — here — another target's output) into the build
+graph as a `WasmComponentInfo`, so the downstream rules can consume it without
+rebuilding from source. See rules_wasm_component#489.
+
+To keep the example hermetic (no binary committed to the repo), `wasm` points
+at an existing built component (`//examples/basic:hello_component`) as a
+stand-in for a prebuilt artifact. In a real pipeline `wasm` would point at an
+`http_file`-fetched release asset (e.g. a flight-control component).
+"""
+
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
+load("@rules_wasm_component//wasm:defs.bzl", "wasm_component_import", "wasm_validate")
+
+wasm_component_import(
+    name = "adopted_component",
+    wasm = "//examples/basic:hello_component",
+)
+
+wasm_validate(
+    name = "adopted_validate",
+    component = ":adopted_component",
+)
+
+build_test(
+    name = "component_import_test",
+    targets = [
+        ":adopted_component",
+        ":adopted_validate",
+    ],
+)

wasm/defs.bzl

@@ -94,6 +94,10 @@ load(
     _wasm_embed_aot = "wasm_embed_aot",
     _wasm_extract_aot = "wasm_extract_aot",
 )
+load(
+    "//wasm/private:wasm_component_import.bzl",
+    _wasm_component_import = "wasm_component_import",
+)
 load(
     "//wasm/private:wasm_optimize.bzl",
     _wasm_optimize = "wasm_optimize",
@@ -157,6 +161,7 @@ wasm_extract_aot = _wasm_extract_aot
 ssh_keygen = _ssh_keygen
 
 # WebAssembly optimization rules
+wasm_component_import = _wasm_component_import
 wasm_optimize = _wasm_optimize
 binaryen_optimize = _binaryen_optimize
 

wasm/private/BUILD.bazel

@@ -139,6 +139,16 @@ bzl_library(
     ],
 )
 
+bzl_library(
+    name = "wasm_component_import",
+    srcs = ["wasm_component_import.bzl"],
+    visibility = [
+        "//docs:__pkg__",
+        "//wasm:__pkg__",
+    ],
+    deps = ["//providers"],
+)
+
 bzl_library(
     name = "wasm_optimize",
     srcs = ["wasm_optimize.bzl"],

wasm/private/wasm_component_import.bzl

@@ -0,0 +1,88 @@
+"""wasm_component_import rule — adopt a prebuilt .wasm component into the graph.
+
+Wraps an already-built (fetched, vendored, or released) WebAssembly component
+file in a `WasmComponentInfo` so the downstream rules (`wasm_validate`,
+`wasm_optimize`, `meld_fuse`, `synth_compile`, signing) can consume it without
+rebuilding it from source.
+
+Motivating use case (rules_wasm_component#489): a consumer adopts a released
+component artifact — e.g. a flight-control `.wasm` fetched via `http_file` — and
+runs validate / optimize / fuse / compile over it. Before this rule that
+required a hand-rolled shim in every consuming repo.
+"""
+
+load("//providers:providers.bzl", "WasmComponentInfo")
+
+def _wasm_component_import_impl(ctx):
+    wasm_file = ctx.file.wasm
+
+    metadata = dict(ctx.attr.metadata)
+    metadata.setdefault("imported", "true")
+    metadata.setdefault("name", ctx.label.name)
+
+    return [
+        DefaultInfo(files = depset([wasm_file])),
+        WasmComponentInfo(
+            wasm_file = wasm_file,
+            # No WIT is recovered from a prebuilt binary here; consumers that
+            # need typed bindings can supply it out of band. None is the
+            # documented "no WIT available" value.
+            wit_info = None,
+            component_type = "component",
+            # Optional, caller-declared interface surface. Left empty when the
+            # caller does not know it — downstream rules must not hard-fail on a
+            # stripped/opaque adopted component.
+            imports = ctx.attr.imports,
+            exports = ctx.attr.exports,
+            metadata = metadata,
+            profile = "release",
+            profile_variants = {},
+        ),
+    ]
+
+wasm_component_import = rule(
+    implementation = _wasm_component_import_impl,
+    doc = """Adopt a prebuilt `.wasm` component as a `WasmComponentInfo` target.
+
+Use this to bring an external/released component into a rules_wasm_component
+build so `wasm_validate`, `wasm_optimize`, `meld_fuse`, `synth_compile`, and the
+signing rules can consume it:
+
+```starlark
+load("@rules_wasm_component//wasm:defs.bzl", "wasm_component_import", "wasm_validate")
+
+wasm_component_import(
+    name = "falcon_flight",
+    wasm = "@falcon_flight_wasm//file",   # e.g. an http_file-fetched release asset
+)
+
+wasm_validate(
+    name = "falcon_validate",
+    component = ":falcon_flight",
+)
+```
+
+`imports`/`exports` are optional and caller-declared; omit them for an opaque
+component (downstream rules tolerate empty lists). `wit_info` is always `None`
+for an imported binary — supply typed bindings out of band if needed.
+""",
+    attrs = {
+        "wasm": attr.label(
+            allow_single_file = [".wasm"],
+            mandatory = True,
+            doc = "The prebuilt WebAssembly component file to adopt.",
+        ),
+        "imports": attr.string_list(
+            default = [],
+            doc = "Optional, caller-declared import interface names. Empty if unknown.",
+        ),
+        "exports": attr.string_list(
+            default = [],
+            doc = "Optional, caller-declared export interface names. Empty if unknown.",
+        ),
+        "metadata": attr.string_dict(
+            default = {},
+            doc = "Optional extra metadata to attach to the WasmComponentInfo.",
+        ),
+    },
+)