bun-src/scripts/build/features-json.ts

/**
 * Host-side `features.json` generation for cross-compiled binaries.
 *
 * `features.json` ships next to every CI artifact and is consumed by the
 * release tooling (packages/bun-release/scripts/upload-s3.ts) and by the
 * crash-report decoder: a crash-report URL carries the enabled-feature set as
 * a VLQ-encoded bitset, and the `features` array here maps bit index → name.
 * Native builds generate it by running the freshly built binary with
 * `scripts/features.mjs` (→ `crash_handler.getFeatureData()`); a
 * cross-compiled binary can't run on the build host, but every field is a
 * build-time constant we already know:
 *
 *   - `features`     — `PACKED_FEATURES_LIST`, a const generated by the
 *                      `define_features!` macro in src/analytics/lib.rs.
 *                      Parsed out of the source below; indices must match
 *                      the binary exactly or crash reports decode wrong.
 *   - `version`      — package.json version (cfg.version)
 *   - `is_canary`    — cfg.canary
 *   - `revision`     — git sha (cfg.revision)
 *   - `generated_at` — wall clock, same as the runtime path
 *
 * test/internal/macos-cross-config.test.ts pins the parser against the real
 * `crash_handler.getFeatureData()` output of a debug build from the same
 * source tree, so a refactor of the macro that breaks the parser fails CI
 * rather than silently shipping a wrong feature table.
 */

import { readFileSync } from "node:fs";
import { resolve } from "node:path";
import { BuildError } from "./error.ts";

/**
 * Extract `PACKED_FEATURES_LIST` from the `define_features! { ... }`
 * invocation in src/analytics/lib.rs without compiling or running anything.
 *
 * Each entry has the shape `<index> => (<rust_ident>, "<feature name>")`.
 * The macro asserts at compile time that the indices are dense 0..N; the
 * same check is repeated here so a parse that silently drops an entry (or a
 * macro reshape the regex doesn't understand) fails the build instead of
 * producing a misaligned feature table.
 */
export function parsePackedFeaturesList(cwd: string): string[] {
  const sourcePath = resolve(cwd, "src", "analytics", "lib.rs");
  const source = readFileSync(sourcePath, "utf8");

  // The macro now recurses internally (`define_features! { @storage ... }`),
  // so several invocation-shaped blocks exist; the entry list is the one whose
  // body contains `<index> => (...)` arms. Scan every block and keep the
  // entries we find — the density check below still rejects partial parses.
  const invocations = [...source.matchAll(/define_features!\s*\{([\s\S]*?)\n\s*\}/g)];
  if (invocations.length === 0) {
    throw new BuildError(`Could not find the define_features! invocation in ${sourcePath}`, {
      hint: "parsePackedFeaturesList() in scripts/build/features-json.ts needs updating to match the new shape.",
    });
  }

  const entries: { index: number; name: string }[] = [];
  // `<index> => (<rust_ident>, "<feature name>")` with an optional
  // `, core = IDENT` alias of the bun_core feature static.
  const entryRe = /(\d+)\s*=>\s*\(\s*\w+\s*,\s*"((?:[^"\\]|\\.)*)"\s*(?:,\s*core\s*=\s*\w+\s*)?\)/g;
  for (const invocation of invocations) {
    for (const m of invocation[1]!.matchAll(entryRe)) {
      entries.push({ index: Number(m[1]), name: m[2]! });
    }
  }
  if (entries.length === 0) {
    throw new BuildError(`Parsed zero entries from define_features! in ${sourcePath}`, {
      hint: "parsePackedFeaturesList() in scripts/build/features-json.ts needs updating to match the new shape.",
    });
  }

  // The bit index is the entry's position in PACKED_FEATURES_LIST. Sort by
  // it and require density, mirroring the macro's own const assert.
  entries.sort((a, b) => a.index - b.index);
  entries.forEach((e, i) => {
    if (e.index !== i) {
      throw new BuildError(
        `define_features! indices are not dense at ${i} (got ${e.index}, feature "${e.name}") — ` +
          `either the source is wrong (the macro's const assert would also fail) or the parser ` +
          `in scripts/build/features-json.ts missed an entry.`,
      );
    }
  });

  return entries.map(e => e.name);
}

/**
 * Build the features.json payload for a binary that can't be executed on
 * the build host. Field set and meaning match `crash_handler.getFeatureData()`
 * (src/runtime/api/crash_handler_jsc.rs) / scripts/features.mjs.
 */
export function crossFeaturesJson(cfg: { cwd: string; version: string; canary: boolean; revision: string }): string {
  return JSON.stringify({
    features: parsePackedFeaturesList(cfg.cwd),
    version: cfg.version,
    is_canary: cfg.canary,
    revision: cfg.revision,
    generated_at: Date.now(),
  });
}