Stop patmat from using selector pos for Try.

It doesn't exist.
Also use symbol with 'ex' name as selector for exceptions

Author: DarkDimius

src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -50,7 +50,8 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
 
   override def transformMatch(tree: Match)(implicit ctx: Context, info: TransformerInfo): Tree = {
     val translated = new Translator()(ctx).translator.translateMatch(tree)
-    translated.ensureConforms(tree.tpe)
+
+    Typed(translated.ensureConforms(tree.tpe), TypeTree(tree.tpe))
   }
 
   class Translator(implicit ctx: Context) {
@@ -1136,7 +1137,13 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
       *   this could probably optimized... (but note that the matchStrategy must be solved for each nested patternmatch)
       */
     def translateMatch(match_ : Match): Tree = {
-      val Match(selector, cases) = match_
+      val Match(sel, cases) = match_
+
+      val selectorTp = elimAnonymousClass(sel.tpe.widen/*withoutAnnotations*/)
+
+      val selectorSym =
+        if (sel ne ExceptionHandlerSel) freshSym(sel.pos, selectorTp, "selector")
+        else freshSym(match_.pos, defn.ThrowableType, "ex")
 
       val (nonSyntheticCases, defaultOverride) = cases match {
         case init :+ last if isSyntheticDefaultCase(last) => (init, Some(((scrut: Symbol) => last.body)))
@@ -1155,23 +1162,20 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
 
       //val start = if (Statistics.canEnable) Statistics.startTimer(patmatNanos) else null
 
-      val selectorTp = elimAnonymousClass(selector.tpe.widen/*withoutAnnotations*/)
-
       // when one of the internal cps-type-state annotations is present, strip all CPS annotations
       ///val origPt  = removeCPSFromPt(match_.tpe)
       // relevant test cases: pos/existentials-harmful.scala, pos/gadt-gilles.scala, pos/t2683.scala, pos/virtpatmat_exist4.scala
       // pt is the skolemized version
       val pt = match_.tpe.widen //repeatedToSeq(origPt)
 
       // val packedPt = repeatedToSeq(typer.packedType(match_, context.owner))
-      val selectorSym = freshSym(selector.pos, selectorTp, "selector")
       selectorSym.setFlag(Flags.SyntheticCase)
 
       // pt = Any* occurs when compiling test/files/pos/annotDepMethType.scala  with -Xexperimental
-      val combined = combineCases(selector, selectorSym, nonSyntheticCases map translateCase(selectorSym, pt), pt, ctx.owner, defaultOverride)
+      val combined = combineCases(sel, selectorSym, nonSyntheticCases map translateCase(selectorSym, pt), pt, ctx.owner, defaultOverride)
 
       // if (Statistics.canEnable) Statistics.stopTimer(patmatNanos, start)
-      Block(List(ValDef(selectorSym,selector)), combined)
+      Block(List(ValDef(selectorSym, sel)), combined)
     }
 
     // return list of typed CaseDefs that are supported by the backend (typed/bind/wildcard)