Function resolveVars

packages/css-data/src/parse-css.ts:111–206

(
  value: string,
  customProperties: Map<string, string>,
  cssVars: Map<string, string> | undefined,
  depth = 0
)

 * recursion depth limit is exceeded.
 */
const resolveVars = (
  value: string,
  customProperties: Map<string, string>,
  cssVars: Map<string, string> | undefined,
  depth = 0
):
  | { resolved: string; dropped: string[]; usedCssVarsSubstitution: boolean }
  | undefined => {
  if (!value.includes("var(") || depth > 8) {
    return;
  }

  let ast: csstree.CssNode;
  try {
    ast = csstree.parse(value, { context: "value", positions: true });
  } catch {
    return;
  }

  const subs: Array<{ start: number; end: number; text: string }> = [];
  const dropped: string[] = [];
  let usedCssVarsSubstitution = false;

  csstree.walk(ast, {
    visit: "Function",
    enter(node) {
      const fnNode = node as csstree.FunctionNode;
      if (fnNode.name !== "var" || !fnNode.loc) {
        return;
      }
      const varRef = parseCssVar(fnNode);
      if (!varRef) {
        return walkSkip;
      }

      const direct =
        customProperties.get(`--${varRef.value}`) ??
        cssVars?.get(`--${varRef.value}`);

      if (direct !== undefined) {
        if (!customProperties.has(`--${varRef.value}`)) {
          usedCssVarsSubstitution = true;
        }
        subs.push({
          start: fnNode.loc.start.offset,
          end: fnNode.loc.end.offset,
          text: direct,
        });
        return walkSkip;
      }

      // Try inline fallback — may itself contain var() references.
      if (varRef.fallback?.type === "unparsed") {
        const fbValue = varRef.fallback.value;
        // If the fallback itself has no var(), use it directly.
        // Otherwise recursively resolve any nested vars inside it.
        const fallbackResult = fbValue.includes("var(")
          ? resolveVars(fbValue, customProperties, cssVars, depth + 1)