Analyzer: deleting a file changes query results

[jensjoha]

TL;DR Deleting a file can cause "find all implementations" query to reduce the number of results (and probably other stuff too).

Reproduction (example):

• Open pkg/_fe_analyzer_shared in an editor.
• Open the file lib/src/parser/listener.dart.
• On class Listener issue a "Find all implementations" query.
• This should give 19 results in 16 files, among them results from front_end and analyzer.
• Create a file and delete it again. This might have to be done from the terminal as deleting a file via VSCode for instance seems to generate a "changed" event instead of a "deleted" event. This command works in Linux at least: touch pkg/_fe_analyzer_shared/lib/x.dart ; sleep 3; rm pkg/_fe_analyzer_shared/lib/x.dart
• On class Listener issue a "Find all implementations" query again.
• This now gives 9 results in 6 files, all in _fe_analyzer_shared.

What happens is, that on the initial "Find all implementations" query a discoverAvailableFiles task is created which basically "discovers" all files in all paths mentioned in the packages file. This is why it finds results in analyzer and front_end. When deleting a file it clears "everything" (removeFile -> _clearFiles in file_state.dart) among it the previously discovered extra files. Issuing the "Find all implementations" query again the discoverAvailableFiles will not do anything as it's already completed, there will thus not be any extra files to search.

/cc @bwilkerson @scheglov

[bwilkerson]

@scheglov Sounds like we need to forget that we've run discoverAvailableFiles so that it will run again.

[jensjoha]

That would probably be one way to go, but wouldn't it make more sense to not throw everything away?
For instance, wouldn't it be possible to for instance just refresh the deleted file instead? (the signature created has both content and a bool exists so I'm assuming that's supported). Or even better, invalidate as-if it had been updated, then remove it from whatever maps it's in. Having to actually run discover available files again isn't exactly free.