introduce a Line class

[chenzhiguang]

The Line is used to maintain the tabRemaining for now.

This is a use case of Line, it can also explain the meaning of the tabRemaining: https://spec.commonmark.org/0.30/#example-6

Normally the > that begins a block quote may be followed optionally by a space, which is not considered part of the content. In the following case > is followed by a tab, which is treated as if it were expanded into three spaces. Since one of these spaces is considered part of the delimiter, foo is considered to be indented six spaces inside the block quote context, so we get an indented code block starting with two spaces.

In this example the tabRemaining is the two spaces from blockquote which will be used in the nested indented code block.

[coveralls]

Pull Request Test Coverage Report for Build 3577142422

• 78 of 85 (91.76%) changed or added relevant lines in 18 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.3%) to 94.615%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/src/block_parser.dart	4	5	80.0%
lib/src/document.dart	2	4	50.0%
lib/src/block_syntaxes/block_syntax.dart	1	5	20.0%
<!--	Total:	78	85	91.76%	-->

Files with Coverage Reduction	New Missed Lines	%
lib/src/util.dart	1	98.18%
lib/src/block_syntaxes/fenced_code_block_syntax.dart	1	98.08%
<!--	Total:	2		-->

Totals
Change from base Build 3542193180:	-0.3%
Covered Lines:	1230
Relevant Lines:	1300

---

💛 - Coveralls

[chenzhiguang]

Can we review this sooner? I need it to create PRs to fix the tab related issues.

[kevmoo]

We'll need to get this working w/ flutter_markdown – which is tricky because the API has changed!

[chenzhiguang]

Yes, I think we can use the same way as we did before to fix it.

[chenzhiguang]

Now it looks better.

[kevmoo]

Help me understand the point of Line? The API is now a bit more complex. What do we get by having a Line construct instead of just using String? (Might be good to have in the change log, too)

[chenzhiguang]

I found It seems the tab issues could be fixed without using this Line type. I will do more research tomorrow.

The idea came from https://github.com/tagnote-app/dart_markdown/blob/master/lib/src/line.dart, but the Line there maintains much more information.

[kevmoo]

Also: mind running benchmarks?

[chenzhiguang]

No difference, I have tried. Let me do it again

[kevmoo]

just because we're allocating a bit more...

[chenzhiguang]

Benchmark before

Benchmark after

[chenzhiguang]

We might need this Line in the future.

[chenzhiguang]

@kevmoo We might still need Line to maintain the tabRemaining, we can not just simply convert the tabRemaining to spaces and prepend them to a string, then passes it to the nested structure.

For example: (See: https://spec.commonmark.org/0.30/#example-5)

- foo

→→bar

There are 2 space sized tabRemaining from the list block, if we just prepend two spaces to →bar like this ..→bar, the output of the indented code block will be: (See: https://spec.commonmark.org/0.30/#example-2)

<pre><code>foo
</code></pre>

More information about tabs behaves: see https://spec.commonmark.org/0.30/#tabs

Tabs in lines are not expanded to spaces. However, in contexts where spaces help to define block structure, tabs behave as if they were replaced by spaces with a tab stop of 4 characters.

Thus, for example, a tab can be used instead of four spaces in an indented code block. (Note, however, that internal tabs are passed through as literal tabs, not expanded to spaces.)

[chenzhiguang]

I have added some more comment for the tabRemaining property of Line.

Sorry for this back and forth, it has been a few months since I created this Line type, I should have written a detailed comment.

[chenzhiguang]

Should we continue? I am blocked by this PR.

[kevmoo]

@srawlins should really chime in here

[chenzhiguang]

What do we say?

[chenzhiguang]

@srawlins Hi Sam, I need your decision in order to plan the next steps. cc @kevmoo

[srawlins]

I will try to get to this today.

[chenzhiguang]

@srawlins Hi Sam, please don’t forget this one.

[chenzhiguang]

No worries! Thanks!