content: Use 17 for base font size, and fix code/mentions/times in headings

[chrisbobbe]

Before	After

Fixes: #512
Fixes: #538

[gnprice]

Thanks for cleaning these up! The code changes all look good to me. A couple of tests are failing, though.

[chrisbobbe]

Those tests are helpful indeed! Hmm. So the problem starts here:

content: Show code, mentions, and times properly even in headings, etc.

The problem is that we're trying to apply the 0.825 fontSize multiplier for inline code in places that don't actually have a fontSize value to apply the multiplier to, e.g. (by the end of the branch), 17 for paragraphs and 23.8 for h1 headings. That will happen when the paragraph/h1/etc. isn't the thing directly surrounding the code span, such as when there's a strong (bold) or emphasis (italic) span around the code span.

The test failure is on this content:

<p><a href="https://a/">two <strong><em><code>words</code></em></strong></a></p>

Here's that content replicated in a CZO message with this Markdown:

[two ***`words`***](https://a/)

The error is:

The following assertion was thrown building InlineContent(dirty, dependencies: [MediaQuery]):
'package:flutter/src/painting/text_style.dart': Failed assertion: line 990 pos 12: 'fontSize != null || (fontSizeFactor == 1.0 && fontSizeDelta == 0.0)': is not true.

The code span is expecting to find a font size on the TextStyle of the surrounding span. That span is an emphasis (italic) span with just const TextStyle(fontStyle: FontStyle.italic)), so no fontSize.

[chrisbobbe]

To fix, we could maybe:

• For every span that might sit between a code span and a paragraph/h1/etc., make sure the span merges into its own style the font size of the span that surrounds it. This seems error-prone.
• In paragraphs/h1s/etc., use a DefaultTextStyle that provides the appropriate font size, and then the code-span code can consume it using DefaultTextStyle.of.

[gnprice]

I like the second direction, and I think we can simplify it: DefaultTextStyle is a way of specifying a style as an inherited widget, to be found from throughout that widget's subtree. But paragraphs and headings etc. are leaves in the widget tree — the further recursion that happens in the ContentNode tree is all producing spans for the one widget, not additional descendant widgets.

So instead of DefaultTextStyle, I think we can pass a style to _InlineContentBuilder as the default style, and then the code-span code can consume that and do the same thing it would do with the result of DefaultTextStyle.of.

[chrisbobbe]

Interesting; thank you! I'll go for that.

[chrisbobbe]

So instead of DefaultTextStyle, I think we can pass a style to _InlineContentBuilder as the default style

Doesn't _InlineContentBuilder already have this, kind of, and call it widget.style? (Except that InlineContent.style is optional, but could easily be made required?)

[gnprice]

Yeah, that seems right. So then that approach comes down to taking widget.style and drawing from it in more places, in the same way you might have done from DefaultTextStyle.of.

[chrisbobbe]

Since #541, we're now using 17 for the base font size.

I plan to close this and open a new PR (-> #544) aimed at #538, with fresh screenshots (that will show the font-size 17 in the "before" column).