[SemanticDB] Missing symbol occurrence on refinement access

[tanishiking]

Compiler version

3.1.1 (#14608)

Minimized code

val a: String = (((1: Any): b.A): Nothing): String
val b: { type A >: Any <: Nothing } = loop()  

Output

sbt> scala3-compiler-bootstrapped/test:runMain dotty.tools.dotc.semanticdb.updateExpect

val a/*<-i5854::B#a.*/: String/*->scala::Predef.String#*/ = (((1: Any/*->scala::Any#*/): b/*->i5854::B#b.*/.A): Nothing/*->scala::Nothing#*/): String/*->scala::Predef.String#*/
val b/*<-i5854::B#b.*/: { type A/*<-local0*/ >: Any/*->scala::Any#*/ <: Nothing/*->scala::Nothing#*/ } = loop/*->i5854::B#loop().*/()

There's no symbol occurrence for b.A on the first line.
see: https://github.com/lampepfl/dotty/blob/ba24fe179c87d1a7a702914aab37e6dd822172c3/tests/semanticdb/expect/i5854.expect.scala

Expectation

val a/*<-i5854::B#a.*/: String/*->scala::Predef.String#*/ = (((1: Any/*->scala::Any#*/): b/*->i5854::B#b.*/.A/*<-local0*/): Nothing/*->scala::Nothing#*/): String/*->scala::Predef.String#*/
val b/*<-i5854::B#b.*/: { type A/*<-local0*/ >: Any/*->scala::Any#*/ <: Nothing/*->scala::Nothing#*/ } = loop/*->i5854::B#loop().*/()

In ExtractSemanticDB, we index the symbols of refinements in a depth first way (type A of b) (because symbols are not attached to the b.A (it only has Name), and then look up the symbol).
However, in the example above, when we try to generate semanticdb symbol, b.A hasn't yet have corresponding symbol in the symbol table. So we fail to retrieve the symbol for b.A.

Possible solutions

• When we encounter the name symbol which doesn't have the corresponding symbol in the symbol table, generate a fake symbol, and somehow treat it as an alias of the "real symbol" (in this case, the symbol of type A (local0)).
• As dotty Namer does, index all the symbols to the symbol table first, and then traverse tree again.