Backport "Refine override exclude criterion for export forwarders" to LTS (#18944)

Backports #17590 to the LTS branch.

PR submitted by the release tooling.

Author: Kordyjan

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1468,8 +1468,8 @@ object Parsers {
      *  PolyFunType    ::=  HKTypeParamClause '=>' Type
      *                   |  HKTypeParamClause ‘->’ [CaptureSet] Type   -- under pureFunctions
      *  FunTypeArgs    ::=  InfixType
-     *                   |  `(' [ [ ‘[using]’ ‘['erased']  FunArgType {`,' FunArgType } ] `)'
-     *                   |  '(' [ ‘[using]’ ‘['erased'] TypedFunParam {',' TypedFunParam } ')'
+     *                   |  `(' [ [ ‘['erased']  FunArgType {`,' FunArgType } ] `)'
+     *                   |  '(' [ ‘['erased'] TypedFunParam {',' TypedFunParam } ')'
      */
     def typ(): Tree =
       val start = in.offset

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1122,7 +1122,10 @@ class Namer { typer: Typer =>
           No("is already an extension method, cannot be exported into another one")
         else if targets.contains(alias) then
           No(i"clashes with another export in the same export clause")
-        else if sym.is(Override) then
+        else if sym.is(Override) || sym.is(JavaDefined) then
+          // The tests above are used to avoid futile searches of `allOverriddenSymbols`.
+          // Scala defined symbols can override concrete symbols only if declared override.
+          // For Java defined symbols, this does not hold, so we have to search anyway.
           sym.allOverriddenSymbols.find(
             other => cls.derivesFrom(other.owner) && !other.is(Deferred)
           ) match

compiler/test/dotc/pos-test-pickling.blacklist

@@ -22,6 +22,7 @@ i15922.scala
 t5031_2.scala
 i16997.scala
 i7414.scala
+i17588.scala
 
 # Tree is huge and blows stack for printing Text
 i7034.scala

tests/pos/i17588.scala

@@ -0,0 +1,2 @@
+class StringBox(inner: String):
+  export inner.*