Check if a prefix is valid before selecting from a type (#22368)

closes #22357

---------

Co-authored-by: Katarzyna Marek <[email protected]>

Author: KacperFKorban

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

@@ -163,7 +163,7 @@ trait TypeAssigner {
           else
             qualType.findMember(name, pre)
 
-        if reallyExists(mbr) then qualType.select(name, mbr)
+        if reallyExists(mbr) && NamedType.validPrefix(qualType) then qualType.select(name, mbr)
         else if qualType.isErroneous || name.toTermName == nme.ERROR then UnspecifiedErrorType
         else NoType
   end selectionType

compiler/test/dotc/neg-best-effort-unpickling.excludelist

@@ -15,3 +15,6 @@ overrideClass.scala
 
 # repeating <error> on a top level type definition
 i18750.scala
+
+# Crash on invalid prefix ([A] =>> Int)
+i22357a.scala

tests/neg/i22357.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i22357.scala:1:0 -----------------------------------------------------------------------------------
+1 |@([A] =>> Int) // error
+  |^^^^^^^^^^^^^^
+  |[A] =>> Int does not have a constructor

tests/neg/i22357.scala

@@ -0,0 +1,2 @@
+@([A] =>> Int) // error
+def i = 1

tests/neg/i22357a.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i22357a.scala:2:6 ----------------------------------------------------------------------------------
+2 |  new ([A] =>> Int)(2) // error
+  |      ^^^^^^^^^^^^^
+  |      [A] =>> Int does not have a constructor

tests/neg/i22357a.scala

@@ -0,0 +1,2 @@
+def main =
+  new ([A] =>> Int)(2) // error