Styled markdown with AttributedString

[laevandus]

🔗 Issue Links

Resolves: IOS-41

🎯 Goal

Use AttributedString's markdown parsing support and apply styling on top of it.

📝 Summary

• UIKit: Change DefaultMarkdownFormatter to use new AttributedString's markdown support
• LLC: Add MarkdownParser (will be used by the SwiftUI SDK)
• Remove SwiftyMarkdown (Remove SwiftyMarkdown #3591)
• Gives stable markdown support (no parsing related crashes anymore)
• Adds missing features like code blocks, applying bold or italic traits in headers
• Remove MarkdownStyles.linkFont because UITextView overrides link attributes

🛠 Implementation

Added MarkdownParser to the LLC which can be used by UIKit and SwiftUI SDKs. It deals with applying additional attributes (injected via a closure because UIKit and SwiftUI use different logic) to various blocks (quote, code, etc). Since SwiftUI text rendering does not support NSParagraphStyle, the extension currently copes with this by adding additional newlines (alternative would have been separate logic for UIKit and SwiftUI, but it felt unnecessary to complicate it so much for our needs).
UIKit also has customisation just for Markdown through MarkdownStyles and MarkdownFont types where the latter is just changes to the default color and font (e.g. I can say that just change font size to 30, but keep using the default font).

Important

MarkdownStyles.linkFont does not really work because we use UITextView in the UIKit for rendering text and UITextView's linkTextAttributes is the one which drives the styling. Therefore, MarkdownStyles.linkFont.color = .green does not actually do anything in the UIKit SDK.

Note

Code blocks would need NSLayoutManager level customisation for background, can't be done with purely AttributedString. Considered this out of scope of this PR.

🎨 Showcase

Before	After

Performance

Compared the performance of the new and old implementation and roughly the new is 2x faster (tried a channel with multiple large messages with markdown).

Before	After

🧪 Manual Testing Notes

• Try various markdown combinations (parsing is similar to GitHub)
• Try various combinations of markdown + mentions (e.g. @username, @userid) + plain links

☑️ Contributor Checklist

• I have signed the Stream CLA (required)
• This change should be manually QAed
• Changelog is updated with client-facing changes
• Changelog is updated with new localization keys
• New code is covered by unit tests
• Documentation has been updated in the docs-content repo

[github-actions]

	2 Warnings
⚠️	Big PR
⚠️	The changes should be manually QAed before the Pull Request will be merged

Generated by 🚫 Danger

[Stream-SDK-Bot]

SDK Performance

target	metric	benchmark	branch	performance	status
MessageList	Hitches total duration	10 ms	7.03 ms	29.7% 🔼	🟢
	Duration	2.6 s	2.55 s	1.92% 🔼	🟢
	Hitch time ratio	4 ms per s	2.75 ms per s	31.25% 🔼	🟢
	Frame rate	75 fps	78.14 fps	4.19% 🔼	🟢
	Number of hitches	1	0.6	40.0% 🔼	🟢

[Stream-SDK-Bot]

SDK Size

title	develop	branch	diff	status
StreamChat	7.02 MB	7.04 MB	+27 KB	🟢
StreamChatUI	4.77 MB	4.68 MB	-92 KB	🚀

[nuno-vieira]

Overall looks good, just asked a couple of questions 👍

[nuno-vieira]

Overall LGTM ✅ Just added a couple of comments. Also, as @martinmitrevski suggested, it would be nice that for code snippets, the whole paragraph as the same background color if possible 🤔

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
89.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[nuno-vieira]

LGTM! ✅