code: private void reportUnrecognizedRequires() {
      for (UnrecognizedRequire unrecognizedRequire : unrecognizedRequires) {
        String legacyNamespace = unrecognizedRequire.legacyNamespace;
  
        Node requireNode = unrecognizedRequire.requireNode;
        boolean targetGoogModuleExists = rewriteState.containsModule(legacyNamespace);
        boolean targetLegacyScriptExists =
            rewriteState.legacyScriptNamespaces.contains(legacyNamespace);
  
        if (!targetGoogModuleExists && !targetLegacyScriptExists) {
          // The required thing was free to be either a goog.module() or a legacy script but neither
          // flavor of file provided the required namespace, so report a vague error.
          compiler.report(
              JSError.make(
                  requireNode,
                  MISSING_MODULE_OR_PROVIDE,
                  legacyNamespace));
          // Remove the require node so this problem isn't reported again in ProcessClosurePrimitives.
          if (!preserveSugar) {
            Node changeScope = NodeUtil.getEnclosingChangeScopeRoot(requireNode);
            if (changeScope == null) {
              // It's already been removed; nothing to do.
            } else {
              compiler.reportChangeToChangeScope(changeScope);
              NodeUtil.getEnclosingStatement(requireNode).detach();
            }
          }
          continue;
        }
  
        // The required thing actually was available somewhere in the program but just wasn't
        // available as early as the require statement would have liked.
        if (unrecognizedRequire.mustBeOrdered) {
          compiler.report(JSError.make(requireNode, LATE_PROVIDE_ERROR, legacyNamespace));
        }
      }
  
      // Clear the queue so that repeated reportUnrecognizedRequires() invocations in hotswap compiles
      // only report new problems.
      unrecognizedRequires.clear();
    }
docs: Examines queue'ed unrecognizedRequires to categorize and report them as either missing module,
  missing namespace or late provide.