Nightly Dotty workflow of 2023-07-05 failed

[github-actions]

See https://github.com/lampepfl/dotty/actions/runs/5460101159

[dwijnand]

 Caused by: java.util.NoSuchElementException: key not found: (com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer@458e2fd5,Replace given matches by a library method)
Error:  	at scala.collection.MapOps.default(Map.scala:274)
Error:  	at scala.collection.MapOps.default$(Map.scala:273)
Error:  	at scala.collection.AbstractMap.default(Map.scala:405)
Error:  	at scala.collection.mutable.HashMap.apply(HashMap.scala:425)
Error:  	at dotty.tools.scaladoc.tasty.comments.markdown.SectionRenderingExtension$SectionHandler$.render(SectionRenderingExtension.scala:36)
Error:  	at dotty.tools.scaladoc.tasty.comments.markdown.SectionRenderingExtension$SectionHandler$.render(SectionRenderingExtension.scala:32)
Error:  	at com.vladsch.flexmark.html.renderer.NodeRenderingHandler.render(NodeRenderingHandler.java:16)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer.renderNode(HtmlRenderer.java:779)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer.renderChildrenNode(HtmlRenderer.java:798)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer.renderChildren(HtmlRenderer.java:790)
Error:  	at com.vladsch.flexmark.html.renderer.CoreNodeRenderer.render(CoreNodeRenderer.java:113)
Error:  	at com.vladsch.flexmark.html.renderer.NodeRenderingHandler.render(NodeRenderingHandler.java:16)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer.renderNode(HtmlRenderer.java:761)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer$MainNodeRenderer.render(HtmlRenderer.java:683)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer.render(HtmlRenderer.java:213)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer.render(HtmlRenderer.java:197)
Error:  	at com.vladsch.flexmark.html.HtmlRenderer.render(HtmlRenderer.java:230)
Error:  	at dotty.tools.scaladoc.site.TemplateFile.resolveInner(templates.scala:128)
Error:  	at dotty.tools.scaladoc.site.LoadedTemplate.resolveToHtml(LoadedTemplate.scala:54)
Error:  	at dotty.tools.scaladoc.renderers.ResolvedTemplate.<init>(SiteRenderer.scala:18)
Error:  	at dotty.tools.scaladoc.renderers.ResolvedTemplate$.apply(SiteRenderer.scala:17)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage(SiteRenderer.scala:25)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage$(SiteRenderer.scala:21)
Error:  	at dotty.tools.scaladoc.renderers.Renderer.templateToPage(Renderer.scala:20)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage$$anonfun$1(SiteRenderer.scala:26)
Error:  	at scala.collection.immutable.List.map(List.scala:250)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage(SiteRenderer.scala:26)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage$(SiteRenderer.scala:21)
Error:  	at dotty.tools.scaladoc.renderers.Renderer.templateToPage(Renderer.scala:20)
Error:  	at dotty.tools.scaladoc.renderers.SiteRenderer.templateToPage$$anonfun$1(SiteRenderer.scala:26)

[smarter]

Same type of error as #18114 and #18070. but failures happen in different projects each time so it doesn't seem to be because of something specific to the projects and rather to an issue in scaladoc or flexmark. It doesn't look like scaladoc changed recently and flexmark hasn't been upgraded either, so this is puzzling /cc @Kordyjan .

[mbovel]

Happened here as well: https://github.com/lampepfl/dotty/actions/runs/5530397761/jobs/10089750052.

[mbovel]

The problem seems to be at https://github.com/lampepfl/dotty/blob/2b391c82de1861d8ab0196e78dd2975539b8082a/scaladoc/src/dotty/tools/scaladoc/tasty/comments/markdown/SectionRenderingExtension.scala#L30-L36

An element is inserted using getOrElseUpdate at line 34 and read directly after at line 36. Yet in some cases, the key is not found. Is this code called concurrently? If yes, could there be a race condition on the update of repeatedIds and should we use a concurrent Map instead?

Code originates from bcdad27. cc @szymon-rd.

[mbovel]

Just saw #18184 that should fix this.

[som-snytt]

I haven't looked at this issue, but as a heads up, scala/scala#10392 caused some incorrect code to fail, where IndexedSeq is involved. Not sure what standard library is in use.