@mui/internal-docs-infra/CodeHighlighter/buildStringFallback.mjs

MUI Infra - internal documentation creation tools.

import { buildRootFallback } from "./fallbackFormat.mjs";
import { parsePlainText } from "../pipeline/parseSource/index.mjs";
function isPromiseLike(value) {
  return typeof value === 'object' && value !== null && typeof value.then === 'function';
}

/**
 * Derive a *windowed* fallback for a plain-string source by running the same
 * `sourceEnhancers` the live render uses over a cheap line-guttered HAST
 * (`parsePlainText` — gutters, no syntax highlighting). The inline-string
 * fallback path otherwise wraps the whole source in one un-windowed focus frame,
 * so an oversized / `@focus` / `@highlight` block paints its full text before
 * hydration then snaps to the collapsed window. Running the enhancers here makes
 * the loading frames match the live render, and the resulting `root.data` carries
 * the `totalLines` / `focusedLines` the compact fallback can't preserve.
 *
 * Synchronous by design — it runs at server fallback-prep time inside the
 * (sync) `prepareInitialSource`. An enhancer that returns a promise is skipped
 * (returns `undefined`) so the caller falls back to the naive single-frame wrap
 * rather than blocking; the built-in `enhanceCodeEmphasis` is synchronous, so
 * the common case windows.
 */
export function buildStringFallback(source, comments, fileName, sourceEnhancers) {
  let root = parsePlainText(source);
  for (const enhancer of sourceEnhancers) {
    const result = enhancer(root, comments, fileName);
    if (isPromiseLike(result)) {
      return undefined;
    }
    root = result;
  }
  const data = root.data;
  const totalLines = data?.totalLines ?? 0;
  const focusedLines = data?.focusedLines ?? totalLines;
  const collapsible = data?.collapsible === true;
  return {
    fallback: buildRootFallback(root),
    totalLines,
    focusedLines,
    collapsible
  };
}