oven-sh/bun · error · Error

build-prefixes.js: could not find the Features bitflags! blo

Error message

build-prefixes.js: could not find the Features bitflags! block in src/css/targets.rs

What it means

build-prefixes.js regenerates the CSS `Features` bitflags block inside src/css/targets.rs. It locates the block by the marker comment `/// Autogenerated by build-prefixes.js` inside a `bitflags::bitflags! {` wrapper; if the regex no longer matches, it refuses to write rather than corrupting the file.

Source

Thrown at src/css/build-prefixes.js:535

    `    /// Autogenerated by build-prefixes.js`,
    `    /// Features to explicitly enable or disable.`,
    `    #[derive(Debug, Clone, Copy, PartialEq, Eq)]`,
    `    pub struct Features: u32 {`,
    ...scalar.map((f, i) => `        const ${f.toUpperCase().padEnd(pad)} = 1 << ${i};`),
    ``,
    ...groups.flatMap(([name, members], i) => {
      const body = members.map(m => `Self::${m.toUpperCase()}.bits()`).join("\n            | ");
      const line = `        const ${name.toUpperCase()} = ${body};`;
      return i > 0 ? [``, line] : [line];
    }),
    `    }`,
    `}`,
  ].join("\n");

  let targets = fs.readFileSync("src/css/targets.rs", "utf8");
  const re = /bitflags::bitflags! \{\n    \/\/\/ Autogenerated by build-prefixes\.js(?:.|\n)+?\n    \}\n\}/;
  if (!re.test(targets)) {
    throw new Error("build-prefixes.js: could not find the Features bitflags! block in src/css/targets.rs");
  }
  targets = targets.replace(re, lines);
  fs.writeFileSync("src/css/targets.rs", targets);
  await rustfmt("src/css/targets.rs");
  console.log("wrote src/css/targets.rs (Features block)");
}

// ─── prefixes.rs ──────────────────────────────────────────────────────────
{
  const variants = [...new Set([...p.keys()].flat().map(enumify))].sort();
  const arms = [];
  for (const [features, versions] of p) {
    const pats = features.map(enumify).join("\n            | ");
    const body = [];
    for (const [name, pfx] of Object.entries(versions)) {
      const inner = [];
      for (const [prefix, [min, max]] of Object.entries(pfx)) {
        if (!prefixConst[prefix]) throw new Error("Missing prefix " + prefix);

View on GitHub (pinned to 8c5296ac45)

Solutions

1. Restore the block structure: start with `bitflags::bitflags! {` followed by ` /// Autogenerated by build-prefixes.js` and close with the matched braces so the regex /bitflags::bitflags! \{\n \/\/\/ Autogenerated by build-prefixes\.js[\s\S]+?\n \}\n\}/ matches.
2. Never edit inside the autogenerated Features region — add new flags to the generator (build-prefixes.js) instead.
3. If targets.rs is too far gone, `git checkout src/css/targets.rs` and rerun the generator.

const re = /bitflags::bitflags! \{\n    \/\/\/ Autogenerated by build-prefixes\.js(?:.|\n)+?\n    \}\n\}/;
const targets = fs.readFileSync("src/css/targets.rs", "utf8");
if (!re.test(targets)) throw new Error("targets.rs: autogenerated Features block marker missing/modified");

When it happens

Trigger: Hand-editing or reformatting the autogenerated Features block in src/css/targets.rs so the marker comment or the `\n }\n}` block structure changed, moved, or was deleted.

Common situations: Running rustfmt with different settings over targets.rs, resolving a merge conflict in the block by rewriting it, or manually adding a feature flag inside the autogenerated region.

Related errors

• Missing prefix ${prefix}
• Virtual CSS module not found: ${path}
• file did not exist after write: ${outputPath}
• Builtin Bundler: do not use import.meta.require() (in ${file
• Errors in ${entrypoint}: ${errors.map(x => x[1]).join("\n")}

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/c09fe0575384b974. Report an issue: GitHub.