mikronova/draupnir

crates/draupnir-build-thing/src/emit.rs

//! **draupnir's half of the emitter** — `code → toml`, one-directional.
//!
//! The WRITER is `nornir_build_thing::emit` (one writer for every repo's recipe
//! crate, lane AG 2026-08-30); what lives here is this repo's own
//! [`EMITTED_HEADER`] and the three calls. The committed
//! `.nornir/build-variants.toml` is [`emitted_toml`]'s output and nothing else:
//! an edit to it has ZERO effect on what the recipe declares
//! (`tests/toml_parity.rs` measures that), and the only way to change the
//! description is to change the code and re-emit.

use std::path::{Path, PathBuf};

use anyhow::Result;
use nornir_build_thing::emit;
use nornir_build_thing::plugin::BuildThing;

use crate::recipe::DraupnirBuildThing;

/// The header every emission starts with — says what the file is, and what it
/// is not.
pub const EMITTED_HEADER: &str = "\
# draupnir — .nornir/build-variants.toml — EMITTED, NOT SOURCE.
#
# Generated by `cargo run -p draupnir-build-thing -- emit` from
# crates/draupnir-build-thing (the Rust `impl BuildThing`). The code is the one
# source; this file DESCRIBES the build for readers and for the tools that
# discover a repo by this path. Editing it changes NOTHING: re-emit after
# changing the code. Do not edit by hand.
#
# Model: variant → features → settings/sub-settings → typ. draupnir ships NO
# executable — it is one crate, one `[lib]`, and every row below is that same
# library with a different backend compiled in. `linkage = \"not-applicable\"` on
# each is a DECLARATION and not an omission: a library is linked by whoever
# consumes it, so the fat/thin axis has no answer, and an omitted key reads as
# the `fat` default (a self-containment claim nobody checked). See
# .nornir/build-thing-design.md for what is declared and why.";

/// The emission — what `.nornir/build-variants.toml` must contain.
pub fn emitted_toml() -> Result<String> {
    emit::emitted_toml(EMITTED_HEADER, &DraupnirBuildThing)
}

/// Regenerate `<repo_root>/.nornir/build-variants.toml` from the code.
pub fn write_emitted(repo_root: &Path) -> Result<PathBuf> {
    emit::write_emitted(EMITTED_HEADER, &DraupnirBuildThing, repo_root)
}

/// The repo root, from this crate's manifest directory.
#[must_use]
pub fn repo_root() -> PathBuf {
    Path::new(env!("CARGO_MANIFEST_DIR"))
        .parent()
        .and_then(Path::parent)
        .expect("crates/draupnir-build-thing has 2 ancestor(s)")
        .to_path_buf()
}

/// The set this recipe declares.
#[must_use]
pub fn declared() -> nornir_build_thing::variant::BuildVariantSet {
    DraupnirBuildThing.variants()
}