Add "sublist" style to MD004 (fixes #21).

doc/Rules.md

@@ -98,7 +98,8 @@ Tags: bullet, ul
 
 Aliases: ul-style
 
-Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")
+Parameters: style ("consistent", "asterisk", "plus", "dash", "sublist"; default
+"consistent")
 
 This rule is triggered when the symbols used in the document for unordered
 list items do not match the configured unordered list style:
@@ -114,9 +115,19 @@ document:
     * Item 2
     * Item 3
 
-Note: the configured list style can be a specific symbol to use (asterisk,
-plus, dash), or simply require that the usage be consistent within the
-document.
+The configured list style can be a specific symbol to use (asterisk, plus, dash),
+can require that usage be consistent within the document, or can require that each
+sublist have a consistent symbol that is different from its parent list.
+
+For example, the following is valid for the `sublist` style because the outer-most
+indent uses asterisk, the middle indent uses plus, and the inner-most indent uses dash:
+
+    * Item 1
+      + Item 2
+        - Item 3
+      + Item 4
+    * Item 4
+      + Item 5
 
 ## MD005 - Inconsistent indentation for list items at the same level
 

lib/rules.js

@@ -224,13 +224,24 @@ module.exports = [
     "aliases": [ "ul-style" ],
     "func": function MD004(params, errors) {
       var style = params.options.style || "consistent";
+      var expectedStyle = style;
+      var nestingStyles = [];
       flattenLists(params).forEach(function forList(list) {
         if (list.unordered) {
-          if (style === "consistent") {
-            style = unorderedListStyleFor(list.items[0]);
+          if (expectedStyle === "consistent") {
+            expectedStyle = unorderedListStyleFor(list.items[0]);
           }
           list.items.forEach(function forItem(item) {
-            if (unorderedListStyleFor(item) !== style) {
+            var itemStyle = unorderedListStyleFor(item);
+            if (style === "sublist") {
+              var nesting = list.nesting;
+              if (!nestingStyles[nesting] &&
+                (itemStyle !== nestingStyles[nesting - 1])) {
+                nestingStyles[nesting] = itemStyle;
+              } else if (itemStyle !== nestingStyles[nesting]) {
+                errors.push(item.lineNumber);
+              }
+            } else if (itemStyle !== expectedStyle) {
               errors.push(item.lineNumber);
             }
           });

test/sublist-bullet-style.json

@@ -0,0 +1,6 @@
+{
+  "default": true,
+  "MD004": {
+    "style": "sublist"
+  }
+}

test/sublist-bullet-style.md

@@ -0,0 +1,56 @@
+1. item
+   1. item
+      + item
+   1. item
+      - item {MD004}
+
+- item
+  * item
+    + item
+      - item
+    + item
+  * item
+- item
+  * item
+    + item
+      - item
+
++ item {MD004}
+  + item {MD004}
+    + item
+      + item {MD004}
+
+- item
+  * item
+    * item {MD004}
+      - item
+        * item
+
++ item {MD004}
+  - item {MD004}
+    * item {MD004}
+
+- item
+  1. item
+     + item
+       1. item
+          * item
+
+1. item
+   * item
+
+- item
+  * item
+    + item
+      - item
+        * item
+          * item {MD004}
+          + item
+
+- item
+  * item
+    + item
+      - item
+        * item
+          - item {MD004}
+          + item