Write correct producers metadata to generated components

crates/fastly-compute-py/Cargo.toml

@@ -23,6 +23,7 @@ wac-graph = "0.8"
 wac-parser = "0.8"
 wit-parser = "0.244"
 wit-component = "0.244"
+wasm-metadata = { version = "0.245", default-features = false }
 tempfile = "3"
 componentize-py = { git = "https://github.com/bytecodealliance/componentize-py" }
 futures = { version = "0.3", default-features = false, features = ["executor"] }
@@ -35,5 +36,6 @@ indexmap = "2"
 
 [build-dependencies]
 anyhow = "1"
+cargo_metadata = "0.23.1"
 wit-parser = "0.219"
 wit-component = "0.219"

crates/fastly-compute-py/build.rs

@@ -8,6 +8,7 @@ fn main() -> Result<()> {
     println!("cargo:rerun-if-changed=../../wit");
     println!("cargo:rerun-if-changed=../../crates/wasiless");
     println!("cargo:rerun-if-changed=../../wrap_app_in_wasiless.wac");
+    println!("cargo:rerun-if-changed=../../Cargo.lock");
 
     let root_dir = PathBuf::from("../../");
     let wit_dir = root_dir.join("wit");
@@ -25,6 +26,20 @@ fn main() -> Result<()> {
         out_dir.join("wrap_app_in_wasiless.wac"),
     )?;
 
+    // Expose the componentize-py version for embedding in Wasm producers metadata.
+    let metadata = cargo_metadata::MetadataCommand::new()
+        .manifest_path(root_dir.join("Cargo.toml"))
+        .exec()
+        .context("Failed to run `cargo metadata`")?;
+    let componentize_py_version = metadata
+        .packages
+        .iter()
+        .find(|p| p.name == "componentize-py")
+        .with_context(|| "componentize-py not found in cargo metadata")?
+        .version
+        .to_string();
+    println!("cargo:rustc-env=COMPONENTIZE_PY_VERSION={componentize_py_version}");
+
     Ok(())
 }
 
@@ -71,7 +86,7 @@ fn build_wasiless_wasm(root_dir: impl AsRef<Path>, out_dir: impl AsRef<Path>) ->
         anyhow::bail!("Failed to build wasiless");
     }
 
-    // Transform wasiless into a component using wasm-tools compnent new
+    // Transform wasiless into a component using wasm-tools component new
     let input_wasm = target_dir.join("wasm32-unknown-unknown/release/wasiless.wasm");
     let output_wasm = out_dir.as_ref().join("wasiless.wasm");
 

crates/fastly-compute-py/src/lib.rs

@@ -10,6 +10,7 @@ use wac_graph::EncodeOptions;
 use wac_parser::Document;
 use wac_types::BorrowedPackageKey;
 use wac_types::Package;
+use wasm_metadata::AddMetadata;
 
 pub mod cli;
 pub mod config;
@@ -168,7 +169,10 @@ pub fn build(output: PathBuf, entry_name: String, virtualenv: Option<PathBuf>) -
     let composed =
         compose_with_wasiless(&temp_component_wasm_path, WASILESS_WASM, WRAP_WAC, &output)?;
 
-    fs::write(&output, composed)
+    log::info!("  Injecting Fastly metadata...");
+    let annotated = inject_fastly_metadata(composed)?;
+
+    fs::write(&output, annotated)
         .with_context(|| format!("Failed to write output: {}", output.display()))?;
 
     log::debug!("Composed output: {}", output.display());
@@ -231,3 +235,56 @@ fn compose_with_wasiless(
 
     Ok(encoded)
 }
+
+/// Inject build tool metadata into the Wasm component's standard `producers`
+/// custom section.
+///
+/// Follows the WebAssembly [Producers Section spec] field conventions:
+///
+/// - `language: Python <version>` — the source language and the CPython
+///   version bundled by componentize-py. Update this when upgrading to a
+///   componentize-py release that bundles a different CPython version.
+/// - `sdk: fastly-compute-py <version>` — the SDK library the user's code is
+///   written against, analogous to `@fastly/js-compute` for the JS SDK.
+/// - `processed-by: componentize-py <version>` — the tool that performed the
+///   core Wasm transformation. `fastly-compute-py` also adds itself here as
+///   the build orchestrator.
+///
+/// Note: the Fastly-proprietary `fastly.manifest.*` custom sections
+/// (language, version, service_id, etc.) are **not** written here. Those are
+/// injected during package ingestion, sourced from the `fastly.toml` manifest
+/// that the CLI bundles alongside the Wasm in the upload package.
+/// Dependency lists, build scripts, and machine info are similarly the CLI's
+/// responsibility via its `fastly_data` producers entry.
+///
+/// [Producers Section spec]: https://github.com/WebAssembly/tool-conventions/blob/main/ProducersSection.md
+fn inject_fastly_metadata(wasm: Vec<u8>) -> Result<Vec<u8>> {
+    let mut add_metadata = AddMetadata::default();
+
+    // Source language. The version is the CPython version bundled by
+    // componentize-py — update this when upgrading to a componentize-py
+    // release that bundles a different CPython version.
+    add_metadata
+        .language
+        .push(("Python".to_owned(), "3.14".to_owned()));
+
+    // The SDK the user's code is written against.
+    add_metadata.sdk.push((
+        "fastly-compute-py".to_owned(),
+        env!("CARGO_PKG_VERSION").to_owned(),
+    ));
+
+    // Tools that performed the Wasm transformation.
+    add_metadata.processed_by.push((
+        "componentize-py".to_owned(),
+        env!("COMPONENTIZE_PY_VERSION").to_owned(),
+    ));
+    add_metadata.processed_by.push((
+        "fastly-compute-py".to_owned(),
+        env!("CARGO_PKG_VERSION").to_owned(),
+    ));
+
+    add_metadata
+        .to_wasm(&wasm)
+        .context("Failed to add producers metadata to Wasm component")
+}

fastly_compute/tests/test_wasm_metadata.py

@@ -0,0 +1,108 @@
+"""Tests for Wasm producers metadata embedded in the built component.
+
+Verifies that all top-level producers section fields written by
+inject_fastly_metadata() are present and correct:
+
+  - language: Python 3.14
+  - sdk: fastly-compute-py 0.1.0
+  - processed-by: componentize-py 0.22.1
+  - processed-by: fastly-compute-py 0.1.0
+
+The language version is also cross-checked against the libpython*.so name
+embedded in the component tree to catch version drift when upgrading
+componentize-py.
+"""
+
+import json
+import re
+import subprocess
+from pathlib import Path
+
+import pytest
+
+WASM_PATH = Path("build/bottle-app.composed.wasm")
+
+# NOTE: these will need to be updated at times but serves as a sanity check
+FASTLY_COMPUTE_PY_VERSION = "0.1.0"
+COMPONENTIZE_PY_VERSION = "0.22.1"
+PYTHON_VERSION = "3.14"
+
+
+@pytest.fixture(scope="module")
+def metadata():
+    """Return the parsed wasm-tools metadata JSON for the built component."""
+    if not WASM_PATH.exists():
+        pytest.fail(f"Built wasm not found at {WASM_PATH}; run `make` first")
+
+    result = subprocess.run(
+        ["wasm-tools", "metadata", "show", "--json", str(WASM_PATH)],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    return json.loads(result.stdout)
+
+
+@pytest.fixture(scope="module")
+def producers(metadata):
+    """Return the top-level producers as a {field: {name: version}} dict."""
+    raw = metadata["component"]["metadata"]["producers"]
+    return dict(raw) if raw else {}
+
+
+def _libpython_version(metadata) -> str | None:
+    """Return the version from the first libpython*.so module name in the tree."""
+    nodes = [metadata]
+    while nodes:
+        node = nodes.pop()
+        kind = next(iter(node))
+        data = node[kind]
+        if kind == "module":
+            name = data.get("name")  # may be None or ""
+            if name:
+                m = re.match(r"libpython(\d+\.\d+)\.so", name)
+                if m:
+                    return m.group(1)
+        else:
+            nodes.extend(data.get("children", []))
+
+
+def test_language_python(producers):
+    assert producers.get("language", {}).get("Python") == PYTHON_VERSION
+
+
+def test_language_python_version_matches_libpython(producers, metadata):
+    """Declared Python version must match the libpython*.so embedded by componentize-py.
+
+    If this fails, update PYTHON_VERSION in this file and the hardcoded version
+    in crates/fastly-compute-py/src/lib.rs.  This is designed to keep us honest
+    and ensure that we don't end up injecting the wrong version as it is
+    not trivial to extract this from compnentize-py directly.
+    """
+    embedded = _libpython_version(metadata)
+    assert embedded is not None, "No libpython*.so module found in component tree"
+    assert producers["language"]["Python"] == embedded, (
+        f"language: Python {producers['language']['Python']!r} does not match "
+        f"embedded libpython{embedded}.so — update PYTHON_VERSION in this file "
+        "and the hardcoded version in crates/fastly-compute-py/src/lib.rs"
+    )
+
+
+def test_sdk_fastly_compute_py(producers):
+    assert (
+        producers.get("sdk", {}).get("fastly-compute-py") == FASTLY_COMPUTE_PY_VERSION
+    )
+
+
+def test_processed_by_componentize_py(producers):
+    assert (
+        producers.get("processed-by", {}).get("componentize-py")
+        == COMPONENTIZE_PY_VERSION
+    )
+
+
+def test_processed_by_fastly_compute_py(producers):
+    assert (
+        producers.get("processed-by", {}).get("fastly-compute-py")
+        == FASTLY_COMPUTE_PY_VERSION
+    )