Fix Binds being read from tasty as if they were type trees.

binds are "shared" as type trees would be shared,
see scala#2510

But they are not type trees, as you can't have them inside TypeApply.
See i2944a.scala.

Author: DarkDimius

compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala

@@ -434,7 +434,8 @@ object TastyFormat {
        | ANDtpt
        | ORtpt
        | BYNAMEtpt
-       | BIND => true
+       | BIND => true // Dmitry: binds are "shared" as type trees would be shared, see https://github.com/lampepfl/dotty/pull/2510
+                      // But they are not type trees, as you can't have them inside TypeApply. See i2944a.scala
     case _ => false
   }
 

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1029,7 +1029,15 @@ class TreeUnpickler(reader: TastyReader, nameAtRef: NameRef => TermName, posUnpi
     }
 
     def readTpt()(implicit ctx: Context) =
-      if (isTypeTreeTag(nextUnsharedTag)) readTerm()
+      if (isTypeTreeTag(nextUnsharedTag)) {
+        val isShared = nextByte == SHARED
+        val term = readTerm()
+        term match {
+          case a: DefTree if isShared =>
+            ref(a.namedType)
+          case _ => term
+        }
+      }
       else {
         val start = currentAddr
         val tp = readType()

tests/pos/i2944.scala

@@ -3,7 +3,6 @@ trait Map2[K] {
   def foo: K = {
     this match {
       case that: Map2[b] => that.get(3.asInstanceOf[b])
-      //case that: Map2[c] => that.get(4.asInstanceOf[K])
       case _ => get(5.asInstanceOf[K])
     }
   }

tests/pos/i2944a.scala

@@ -0,0 +1,8 @@
+trait Map2[K] {
+  def get(k: K): K = k
+  def foo: K = {
+    this match {
+      case that: Map2[c] => that.get(4.asInstanceOf[K])
+    }
+  }
+}