Incorrect unordered list structure, when indented by tabs #2172

Currently, if we try to parse list like that

* one
\t* nested one
\t* nested two

* two

it would be parsed into following structure

• one
  • nested one
    • nested two
• two

while it's expected to be

• one
  • nested one
  • nested two
• two

After lots of debugging I found that in the list_syntax.dart file, in the parse method, there are two variables indent and currentIndent that are crucial to detect nested list.
And the currentIndent is calculated as:

final currentIndent = parser.current.content.indentation() +
          (parser.current.tabRemaining ?? 0);

while indent in this case is calculated as

indent = precedingWhitespaces + contentWhitespances

In the case above, when we have list indented by tabs, we have tabRemaining as 2 for both nested lines of second level, but because indent is not taking into account tabRemaining there, it mistakenly adds unwanted nesting later, when we compare indent <= currentIndent (which is 2 <= 2 for the "nested two" element).

So my suggested fix is to change indent calculation by adding tabRemaining there:

indent = precedingWhitespaces +
              contentWhitespances +
              (parser.current.tabRemaining ?? 0)

That way all tests are passing. But I'm not sure if we should also add the same fix to contentWhitespances >= 4 branch above, and I couldn't find a test case for that branch.

Could someone please validate the fix? Thanks!