Incorrect closing sourcepos column for code blocks

[oampo]

The sourcepos attribute for code blocks reports the column number for the line before the end of the block.

Here's a quick test case:

const commonmark = require('commonmark');
const parser = new commonmark.Parser();

// Annotated with line numbers
// 1 ```
// 2 hello world
// 3 ```
const md = '```\nhello world\n```';

const node = parser.parse(md);

const walker = node.walker();

while ((event = walker.next())) {
    const {node} = event;
    if (node.type === 'code_block') {
        console.log(node.sourcepos);
    }
}

I'd expect to see [[1, 1], [3, 3]] - the backticks start at L1C1 and end at L3C3. Instead, I see [[1, 1], [3, 11]], where the closing column number (11) is the length of the hello world line before the closing backticks.

[SonyaOrlova]

i have the same problem with comments (html_block)
example:

# Example
<!-- this is a comment -->

for the comment i expect to see the following sourcepos [2, 1] [2, 26], but i get [2, 1] [2, 9]

adding this.lastLineLength = ln.length; before this.finalize here

commonmark.js/lib/blocks.js

Line 772 in ffc5d87

this.finalize(container, this.lineNumber);

solves the problem

and one more interesting thing: if i add several spaces before comment, like this:

# Example
    <!-- this is a comment -->

i get code_block type instead of html_block, and correct sourcepos

[jgm]

Thanks for reporting!