@mui/internal-docs-infra/pipeline/loadIsomorphicCodeVariant/getInitialVisibleSourceLines.mjs

MUI Infra - internal documentation creation tools.

import { COLLAPSED_VISIBLE_FRAME_TYPES } from "../parseSource/frameVisibility.mjs";
import { isFrameSpan } from "../parseSource/isFrameSpan.mjs";

/**
 * Returns the set of 1-indexed source line numbers that are visible when
 * the rendered code block is collapsed (i.e. the user hasn't clicked
 * "expand"). Mirrors the visibility rule applied at runtime by `<Pre>`:
 *
 *   - Frames whose `data-frame-type` is `'highlighted'`, `'focus'`,
 *     `'padding-top'`, or `'padding-bottom'` are visible.
 *   - When no such emphasis frame exists, only the first frame is shown
 *     (this matches `getInitialVisibleFrames` in `<Pre>`).
 *
 * `tree` must be the output of `parseSource` (a `Root` whose top-level
 * children are frame `Element`s with `'line'` `Element` descendants).
 * Returns an empty set for an empty/invalid tree.
 */
export function getInitialVisibleSourceLines(tree) {
  const visible = new Set();
  if (tree.type !== 'root') {
    return visible;
  }
  const root = tree;
  let lineNumber = 0;
  let hasVisibleEmphasisFrame = false;
  // First pass: collect lines under explicitly-visible emphasis frames.
  for (const child of root.children) {
    if (child.type !== 'element' || !isFrameSpan(child)) {
      continue;
    }
    const frame = child;
    const frameType = frame.properties?.dataFrameType;
    const frameVisible = typeof frameType === 'string' && COLLAPSED_VISIBLE_FRAME_TYPES.has(frameType);
    if (frameVisible) {
      hasVisibleEmphasisFrame = true;
    }
    for (const grandChild of frame.children) {
      if (grandChild.type === 'element' && grandChild.properties?.className === 'line') {
        lineNumber += 1;
        if (frameVisible) {
          visible.add(lineNumber);
        }
      }
    }
  }

  // Collapse-to-nothing (oversizedFocus: 'hide'): the source records
  // `focusedLines === 0`, meaning the collapsed window is intentionally empty.
  // Skip the first-frame fallback so nothing is shown when collapsed.
  if (root.data?.focusedLines === 0) {
    return visible;
  }

  // Fallback: no emphasis frame in the source — the first frame is the
  // one shown when collapsed. Add its lines.
  if (!hasVisibleEmphasisFrame && lineNumber > 0) {
    let fallbackLine = 0;
    for (const child of root.children) {
      if (child.type !== 'element' || !isFrameSpan(child)) {
        continue;
      }
      const frame = child;
      for (const grandChild of frame.children) {
        if (grandChild.type === 'element' && grandChild.properties?.className === 'line') {
          fallbackLine += 1;
          visible.add(fallbackLine);
        }
      }
      // Only the first frame.
      break;
    }
  }
  return visible;
}