Make item loop iterative (vs. recursive) to handle synchronous processing of thousands of items.

lib/markdownlint.js

@@ -445,14 +445,21 @@ function lintInput(options, synchronous, callback) {
   var resultVersion = (options.resultVersion === undefined) ?
     2 : options.resultVersion;
   var results = newResults(ruleList);
-  // Helper to lint the next string or file item
+  // Helper to lint the next string or file
+  function lintNextItem() {
+    var iterating = true;
     var item = null;
-  function lintNextItem(err, result) {
+    function lintNextItemCallback(err, result) {
       if (err) {
+        iterating = false;
         return callback(err);
-    } else if (result) {
-      results[item] = result;
       }
+      results[item] = result;
+      if (!iterating) {
+        lintNextItem();
+      }
+    }
+    while (iterating) {
       if ((item = stringsKeys.shift())) {
         lintContent(
           ruleList,
@@ -461,8 +468,9 @@ function lintInput(options, synchronous, callback) {
           frontMatter,
           noInlineConfig,
           resultVersion,
-        lintNextItem);
+          lintNextItemCallback);
       } else if ((item = files.shift())) {
+        iterating = synchronous;
         lintFile(
           ruleList,
           item,
@@ -471,9 +479,10 @@ function lintInput(options, synchronous, callback) {
           noInlineConfig,
           resultVersion,
           synchronous,
-        lintNextItem);
+          lintNextItemCallback);
       } else {
-      callback(null, results);
+        return callback(null, results);
+      }
     }
   }
   lintNextItem();