bugfix: Check if symbol exists before calling methods on it

Fixes #23374

Author: tgodzik

compiler/src/dotty/tools/dotc/semanticdb/ExtractSemanticDB.scala

@@ -320,27 +320,27 @@ object ExtractSemanticDB:
                 registerDefinition(tree.symbol, selectSpan(tree), Set.empty, tree.source)
               case tree => registerDefinition(tree.symbol, tree.span, Set.empty, tree.source)
         case tree: NamedDefTree =>
-          if !tree.symbol.isAllOf(ModuleValCreationFlags) then
+          if tree.symbol.exists && !tree.symbol.isAllOf(ModuleValCreationFlags) then
             tree match {
-              case tree: ValDef if tree.symbol.isAllOf(EnumValue) =>
+              case tree: ValDef if tree.symbol.exists && tree.symbol.isAllOf(EnumValue) =>
                 tree.rhs match
                 case Block(TypeDef(_, template: Template) :: _, _) => // simple case with specialised extends clause
                   template.parents.filter(!_.span.isZeroExtent).foreach(traverse)
                 case _ => // calls $new
-              case tree: ValDef if tree.symbol.isSelfSym =>
+              case tree: ValDef if tree.symbol.exists && tree.symbol.isSelfSym =>
                 if tree.tpt.span.hasLength then
                   traverse(tree.tpt)
-              case tree: DefDef if tree.symbol.isConstructor => // ignore typeparams for secondary ctors
+              case tree: DefDef if tree.symbol.exists && tree.symbol.isConstructor => // ignore typeparams for secondary ctors
                 tree.trailingParamss.foreach(_.foreach(traverse))
                 traverse(tree.rhs)
-              case tree: (DefDef | ValDef) if tree.symbol.isSyntheticWithIdent =>
+              case tree: (DefDef | ValDef) if tree.symbol.exists && tree.symbol.isSyntheticWithIdent =>
                 tree match
                   case tree: DefDef =>
                     tree.paramss.foreach(_.foreach(param => registerSymbolSimple(param.symbol)))
-                  case tree: ValDef if tree.symbol.is(Given) =>
+                  case tree: ValDef if tree.symbol.exists && tree.symbol.is(Given) =>
                     traverse(tree.tpt)
                   case _ =>
-                if !tree.symbol.isGlobal then
+                if tree.symbol.exists && !tree.symbol.isGlobal then
                   localBodies(tree.symbol) = tree.rhs
                 // ignore rhs
 
@@ -379,7 +379,7 @@ object ExtractSemanticDB:
             traverseAnnotsOfDefinition(ctorSym)
             ctorParams(tree.constr.termParamss, tree.constr.leadingTypeParams, tree.body)
             registerDefinition(ctorSym, tree.constr.nameSpan.startPos, Set.empty, tree.source)
-        case tree: Apply =>
+        case tree: Apply if tree.fun.symbol.exists =>
           @tu lazy val genParamSymbol: Name => String = tree.fun.symbol.funParamSymbol
           traverse(tree.fun)
           synth.tryFindSynthetic(tree).foreach(synthetics.addOne)