Write correct producers metadata to generated components

These changes updates fastly-compute-py to inject appropriate
producer metadata to our generated component at the top-level.
Here's what we get with this change:

    $ wasm-tools metadata show build/bottle-app.composed.wasm --json | jq '.component.metadata.producers[]'
    [
      "language",
      {
        "Python": "3.14"
      }
    ]
    [
      "processed-by",
      {
        "componentize-py": "0.22.1",
        "fastly-compute-py": "0.1.0"
      }
    ]
    [
      "sdk",
      {
        "fastly-compute-py": "0.1.0"
      }
    ]

Author: posborne

Cargo.lock

@@ -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/Cargo.toml

@@ -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/build.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;
@@ -166,7 +167,10 @@ 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());
@@ -229,3 +233,56 @@ 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")
+}