Generation of semanticdb for dotty codebase fails

[kpbochenek]

enable flag "-Ysemanticdb" for compilation of dotty. It will cause build to fail.

Semanticdb is needed by metals to provide basic functionality for editors(find references/goto definition).

Here I created a branch showing where things fail what workarounds I did to make compilation succeed -> generate .semanticdb to let metals provide minimal support and how I enabled semanticdb generation(in case I messed up something :P).
https://github.com/kpbochenek/dotty/pull/1/files

Problem 1:
There is a function
file:ExtractSemanticDB.scala: private def adjustSpanToName(span: Span, qualSpan: Span, name: Name)(using Context) =
It throws exception that tries to access characters outside of current source file. It happens for a file:
dotty/library/src/scala/quoted/autolift.scala 261 with 862 FOR [834..844..863] AND FunctionalInterface
(it means autolift.scala file with 261 characters but it tries to access Span in range 834-863 of name FunctionalInterface)

Problem 2:
When problem1 is fixed(or worked around) you hit problem 2.

[error] ## Exception when compiling 444 sources to <...>/dotty/compiler/target/scala-0.24/classes
[error] java.lang.AssertionError: NoDenotation.owner
[error] dotty.tools.dotc.core.SymDenotations$NoDenotation$.owner(SymDenotations.scala:2330)
[error] dotty.tools.dotc.semanticdb.ExtractSemanticDB$Extractor.traverseTpt$1$$anonfun$1(ExtractSemanticDB.scala:119)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] dotty.tools.dotc.semanticdb.ExtractSemanticDB$Extractor.traverse$$anonfun$17$$anonfun$1(ExtractSemanticDB.scala:576)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.semanticdb.ExtractSemanticDB$Extractor.traverse$$anonfun$7(ExtractSemanticDB.scala:576)
...

This one I have not checked more but workaround with try catch shows for now there is no more compilation error issues.

[bishabosha]

so sometimes the source associated with a tree is not the same as the compilation unit, which can solve the span issue, The knock on effect of stopping the span crash is then a separate bug

[bishabosha]

whats more weird is that the issue with compiling dotty/library/src/scala/quoted/autolift.scala is that apparently it only crashes with a clean compile of dotty, and not just dotc on that file alone, perhaps some other flags are interfering