[markdown mode] Fix indentation rules to match CommonMark

See http://spec.commonmark.org/0.24/#list-items

Closes codemirror#3833

Author: 0b10011

mode/markdown/markdown.js

@@ -149,10 +149,8 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
         state.list = null;
       } else if (state.indentation > 0) {
         state.list = null;
-        state.listDepth = Math.floor(state.indentation / 4);
       } else { // No longer a list
         state.list = false;
-        state.listDepth = 0;
       }
     }
 
@@ -199,7 +197,17 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
       }
       state.indentation = stream.column() + stream.current().length;
       state.list = true;
-      state.listDepth++;
+
+      // While this list item's marker's indentation
+      // is less than the deepest list item's content's indentation,
+      // pop the deepest list item indentation off the stack.
+      while (state.listStack && stream.column() < state.listStack[state.listStack.length - 1]) {
+        state.listStack.pop();
+      }
+
+      // Add this list item's content's indentation to the stack
+      state.listStack.push(state.indentation);
+
       if (modeCfg.taskLists && stream.match(taskListRE, false)) {
         state.taskList = true;
       }
@@ -321,7 +329,7 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
     }
 
     if (state.list !== false) {
-      var listMod = (state.listDepth - 1) % 3;
+      var listMod = (state.listStack.length - 1) % 3;
       if (!listMod) {
         styles.push(tokenTypes.list1);
       } else if (listMod === 1) {
@@ -697,7 +705,7 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
         hr: false,
         taskList: false,
         list: false,
-        listDepth: 0,
+        listStack: [],
         quote: 0,
         trailingSpace: 0,
         trailingSpaceNewLine: false,
@@ -732,7 +740,7 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
         hr: s.hr,
         taskList: s.taskList,
         list: s.list,
-        listDepth: s.listDepth,
+        listStack: s.listStack.slice(0),
         quote: s.quote,
         indentedCode: s.indentedCode,
         trailingSpace: s.trailingSpace,
@@ -772,11 +780,8 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
 
         state.f = state.block;
         var indentation = stream.match(/^\s*/, true)[0].replace(/\t/g, '    ').length;
-        var difference = Math.floor((indentation - state.indentation) / 4) * 4;
-        if (difference > 4) difference = 4;
-        var adjustedIndentation = state.indentation + difference;
-        state.indentationDiff = adjustedIndentation - state.indentation;
-        state.indentation = adjustedIndentation;
+        state.indentationDiff = Math.min(indentation - state.indentation, 4);
+        state.indentation = state.indentation + state.indentationDiff;
         if (indentation > 0) return null;
       }
       return state.f(stream, state);

mode/markdown/test.js

@@ -452,6 +452,18 @@
      "",
      "hello");
 
+  MT("listCommonMarkIndentationCode",
+     "[variable-2 * Code blocks also affect]",
+     "  [variable-3 * The next level starts where the contents start.]",
+     "   [variable-3 *    Anything less than that will keep the item on the same level.]",
+     "       [variable-3 * Each list item can indent the first level further and further.]",
+     "  [variable-3 * For the most part, this makes sense while writing a list.]",
+     "    [keyword * This means two items with same indentation can be different levels.]",
+     "     [keyword *  Each level has an indent requirement that can change between items.]",
+     "       [keyword * A list item that meets this will be part of the next level.]",
+     "   [variable-3 * Otherwise, it will be part of the level where it does meet this.]",
+     " [variable-2 * World]");
+
   // Blockquote
   MT("blockquote",
      "[variable-2 * foo]",