Emit language variants for articles

[franklinsch]

Bug/issue #, if applicable: rdar://88464797

Summary

Articles that document a module available in multiple languages now inherit that module's languages. This ensures that we generate multiple language variants for article pages.

While investigating the performance impact of this change, I found that the repeated accesses to the DocumentationContext.rootModules (a computed property that iterates over all topic graph nodes) was causing a large performance regression. To resolve this, in the second commit I made the property a stored property instead that's initialised once during bundle registration, right after symbols have been loaded in the symbol graph.

Performance impact

No statistically significant impact.

Size 10
+-----------------------------------------------------------------------------------------------------+
| Metric                                   | Change     | Before               | After                |
+-----------------------------------------------------------------------------------------------------+
| Compiled output size (MB)                | no change  | 114.68               | 114.68               |
| Duration for 'bundle-registration' (sec) | +1.58%     | 5.76                 | 5.85                 |
| Duration for 'convert-action' (sec)      | +2.93%     | 7.78                 | 8.00                 |
| Peak memory footprint (MB)               | -1.18%     | 354.33               | 350.14               |
| Topic Anchor Checksum                    | no change  | c8f03d4e81da8e3b6d7f | c8f03d4e81da8e3b6d7f |
| Topic Graph Checksum                     | no change  | edce22bce4f8de475a5e | edce22bce4f8de475a5e |
+-----------------------------------------------------------------------------------------------------+

Size 25
+-----------------------------------------------------------------------------------------------------+
| Metric                                   | Change     | Before               | After                |
+-----------------------------------------------------------------------------------------------------+
| Compiled output size (MB)                | no change  | 287.62               | 287.62               |
| Duration for 'bundle-registration' (sec) | +0.26%     | 14.75                | 14.79                |
| Duration for 'convert-action' (sec)      | -0.03%     | 20.09                | 20.08                |
| Peak memory footprint (MB)               | -0.68%     | 816.43               | 810.91               |
| Topic Anchor Checksum                    | no change  | 9a675b9ad6d69f8b7f0c | 9a675b9ad6d69f8b7f0c |
| Topic Graph Checksum                     | no change  | 665713509084b5131a37 | 665713509084b5131a37 |
+-----------------------------------------------------------------------------------------------------+

Size 5
+-----------------------------------------------------------------------------------------------------+
| Metric                                   | Change     | Before               | After                |
+-----------------------------------------------------------------------------------------------------+
| Compiled output size (MB)                | no change  | 57.36                | 57.36                |
| Duration for 'bundle-registration' (sec) | -0.31%     | 2.94                 | 2.93                 |
| Duration for 'convert-action' (sec)      | -0.51%     | 3.95                 | 3.93                 |
| Peak memory footprint (MB)               | -5.21%     | 209.86               | 198.93               |
| Topic Anchor Checksum                    | no change  | 65d4ff3050cd1106a21b | 65d4ff3050cd1106a21b |
| Topic Graph Checksum                     | no change  | 0a64c740a2ed5a246836 | 0a64c740a2ed5a246836 |
+-----------------------------------------------------------------------------------------------------+

Size 50
+-----------------------------------------------------------------------------------------------------+
| Metric                                   | Change     | Before               | After                |
+-----------------------------------------------------------------------------------------------------+
| Compiled output size (MB)                | no change  | 578.63               | 578.63               |
| Duration for 'bundle-registration' (sec) | -1.07%     | 30.17                | 29.84                |
| Duration for 'convert-action' (sec)      | +0.47%     | 41.06                | 41.25                |
| Peak memory footprint (MB)               | -0.90%     | 1552.76              | 1538.81              |
| Topic Anchor Checksum                    | no change  | 08d0a84bec913460905f | 08d0a84bec913460905f |
| Topic Graph Checksum                     | no change  | 74d25c4f1ee185ad5676 | 74d25c4f1ee185ad5676 |
+-----------------------------------------------------------------------------------------------------+

Dependencies

None.

Testing

When documenting a framework that supports Swift and Objective-C, verify that articles, whether they're automatically or manually curated, get the language switcher in the sidebar. The syntax used in symbol references should reflect the currently selected language.

TODO

• Investigate performance impact

Checklist

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[franklinsch]

@swift-ci please test

[Kyle-Ye]

Also I suggest changing the "name" and "id" definitions in SourceLanguage.swift from "var" to "let" by the way.

https://github.com/apple/swift-docc/blob/779ca826b7902880477a3bfcc0078970284fb505/Sources/SwiftDocC/Model/SourceLanguage.swift#L12-L16

[franklinsch]

@swift-ci test

[ethan-kusters]

Looks good! Thanks for putting this together.

I remember when initially implementing #47 that there was some remaining work to support auto-curated symbol collections (for protocol inherited symbols and the like) in multi-language scenarios since those rely on articles. Is that something we can resolve in this PR? (Or are we already and I missed it?)

[ethan-kusters]

Nit:

Suggested change

	let sourceLanguage = availableSourceLanguages.map { availableSourceLanguages in
	let defaultSourceLanguage = availableSourceLanguages.map { availableSourceLanguages in

[ethan-kusters]

This snippet check is a little confusing to me. Maybe we should consider a node.isSnippetModule property at some point?

It almost seems like we should have a separate kind .snippetModule if we're going to need to special-case these.

[franklinsch]

Sounds good to me. This logic was just moved in this PR, but we should consider revisiting this in the future.

[franklinsch]

I remember when initially implementing #47 that there was some remaining work to support auto-curated symbol collections (for protocol inherited symbols and the like) in multi-language scenarios since those rely on articles. Is that something we can resolve in this PR? (Or are we already and I missed it?)

I don't think that would be affected by these changes. This PR should only affect user-authored articles. Do we have a bug to track the issue you're referring to?

[ethan-kusters]

@swift-ci please test