Function highlightLine

packages/color-diff-napi/src/index.ts:511–545

(
  state: { lang: string | null; stack: unknown },
  line: string,
  theme: Theme,
)

let loggedEmitterShapeError = false

function highlightLine(
  state: { lang: string | null; stack: unknown },
  line: string,
  theme: Theme,
): Block[] {
  // syntect-parity: feed a trailing \n so line comments terminate, then strip
  const code = line + '\n'
  if (!state.lang) {
    return [[defaultStyle(theme), code]]
  }
  let result
  try {
    result = hljs().highlight(code, {
      language: state.lang,
      ignoreIllegals: true,
    })
  } catch {
    // hljs throws on unknown language despite ignoreIllegals
    return [[defaultStyle(theme), code]]
  }
  if (!hasRootNode(result.emitter)) {
    if (!loggedEmitterShapeError) {
      loggedEmitterShapeError = true
      logError(
        new Error(
          `color-diff: hljs emitter shape mismatch (keys: ${Object.keys(result.emitter).join(',')}). Syntax highlighting disabled.`,
        ),
      )
    }
    return [[defaultStyle(theme), code]]
  }
  const blocks: Block[] = []
  flattenHljs(result.emitter.rootNode, theme, undefined, blocks)
  return blocks
}

// ---------------------------------------------------------------------------
// Word diff