Allow opt-out for list items with blank lines in MD009/no-trailing-spaces (fixes #55).

doc/Rules.md

@@ -254,20 +254,28 @@ Tags: whitespace
 
 Aliases: no-trailing-spaces
 
-Parameters: br_spaces (number; default 0)
+Parameters: br_spaces, list_item_empty_lines (number; default 0, boolean; default false)
 
 This rule is triggered on any lines that end with whitespace. To fix this,
 find the line that is triggered and remove any trailing spaces from the end.
 
-The br_spaces parameter allows an exception to this rule for a specific amount
+The `br_spaces` parameter allows an exception to this rule for a specific amount
 of trailing spaces used to insert an explicit line break/br element. For
-example, set br_spaces to 2 to allow exactly 2 spaces at the end of a line.
+example, set `br_spaces` to 2 to allow exactly 2 spaces at the end of a line.
 
-Note: you have to set br_spaces to 2 or higher for this exception to take
+Note: you have to set `br_spaces` to 2 or higher for this exception to take
 effect - you can't insert a br element with just a single trailing space, so
-if you set br_spaces to 1, the exception will be disabled, just as if it was
+if you set `br_spaces` to 1, the exception will be disabled, just as if it was
 set to the default of 0.
 
+Using spaces to indent blank lines inside a list item is usually not necessary,
+but some parsers require it. Set the `list_item_empty_lines` parameter to `true`
+to allow this:
+
+    - list item text
+      
+      list item text
+
 <a name="md010"></a>
 
 ## MD010 - Hard tabs

lib/rules.js

@@ -353,10 +353,23 @@ module.exports = [
     "regexp": trailingSpaceRe,
     "func": function MD009(params, errors) {
       var brSpaces = params.options.br_spaces || 0;
+      var listItemEmptyLines = params.options.list_item_empty_lines;
+      var allowListItemEmptyLines =
+        (listItemEmptyLines === undefined) ? false : !!listItemEmptyLines;
+      var listItemLineNumbers = [];
+      if (allowListItemEmptyLines) {
+        filterTokens(params, "list_item_open", function forToken(token) {
+          for (var i = token.map[0]; i < token.map[1]; i++) {
+            listItemLineNumbers.push(i + 1);
+          }
+        });
+      }
       forEachLine(params, function forLine(line, lineIndex) {
-        if (trailingSpaceRe.test(line)) {
+        var lineNumber = lineIndex + 1;
+        if (trailingSpaceRe.test(line) &&
+          (listItemLineNumbers.indexOf(lineNumber) === -1)) {
           var expected = (brSpaces < 2) ? 0 : brSpaces;
-          errors.addDetailIf(lineIndex + 1,
+          errors.addDetailIf(lineNumber,
             expected, line.length - line.trimRight().length);
         }
       });

schema/build-config-schema.js

@@ -91,6 +91,11 @@ rules.forEach(function forRule(rule) {
           "description": "Spaces for line break",
           "type": "integer",
           "default": 0
+        },
+        "list_item_empty_lines": {
+          "description": "Allow spaces for empty lines in list items",
+          "type": "boolean",
+          "default": false
         }
       };
       break;

schema/markdownlint-config-schema.json

@@ -207,6 +207,11 @@
           "description": "Spaces for line break",
           "type": "integer",
           "default": 0
+        },
+        "list_item_empty_lines": {
+          "description": "Allow spaces for empty lines in list items",
+          "type": "boolean",
+          "default": false
         }
       },
       "additionalProperties": false
@@ -223,6 +228,11 @@
           "description": "Spaces for line break",
           "type": "integer",
           "default": 0
+        },
+        "list_item_empty_lines": {
+          "description": "Allow spaces for empty lines in list items",
+          "type": "boolean",
+          "default": false
         }
       },
       "additionalProperties": false

test/trailing-spaces-in-lists-allowed.json

@@ -0,0 +1,6 @@
+{
+  "default": true,
+  "MD009": {
+    "list_item_empty_lines": true
+  }
+}

test/trailing-spaces-in-lists-allowed.md

@@ -0,0 +1,52 @@
+# Heading
+
+1. text
+   text
+1. text
+
+   text
+1. text
+   
+   text
+1. text
+   text
+
+1. text
+   text
+   
+1. text
+   
+{MD009:16}
+{MD009:18}
+
+1. text
+   text
+   1. text
+
+      text
+   1. text
+      
+      text
+   1. text
+      text
+
+   1. text
+      text
+      
+   1. text
+      
+1. text
+   - text
+
+     text
+   - text
+     
+     text
+   - text
+     text
+
+   - text
+     text
+     
+{MD009:37}
+{MD009:50}

test/trailing-spaces-in-lists-default.md

@@ -0,0 +1,56 @@
+# Heading
+
+1. text
+   text
+1. text
+
+   text
+1. text
+   
+   text
+1. text
+   text
+
+1. text
+   text
+   
+1. text
+   
+{MD009:9}
+{MD009:16}
+{MD009:18}
+
+1. text
+   text
+   1. text
+
+      text
+   1. text
+      
+      text
+   1. text
+      text
+
+   1. text
+      text
+      
+   1. text
+      
+1. text
+   - text
+
+     text
+   - text
+     
+     text
+   - text
+     text
+
+   - text
+     text
+     
+{MD009:29}
+{MD009:36}
+{MD009:38}
+{MD009:44}
+{MD009:51}