fix issue 20901: etaCollapse context bound type

Author: bishabosha

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

@@ -2366,13 +2366,14 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
 
   def typedContextBoundTypeTree(tree: untpd.ContextBoundTypeTree)(using Context): Tree =
     val tycon = typedType(tree.tycon)
-    val tyconSplice = untpd.TypedSplice(tycon)
+    def spliced(tree: Tree) = untpd.TypedSplice(tree)
     val tparam = untpd.Ident(tree.paramName).withSpan(tree.span)
     if tycon.tpe.typeParams.nonEmpty then
-      typed(untpd.AppliedTypeTree(tyconSplice, tparam :: Nil))
+      val tycon0 = tycon.withType(tycon.tpe.etaCollapse)
+      typed(untpd.AppliedTypeTree(spliced(tycon0), tparam :: Nil))
     else if Feature.enabled(modularity) && tycon.tpe.member(tpnme.Self).symbol.isAbstractOrParamType then
       val tparamSplice = untpd.TypedSplice(typedExpr(tparam))
-      typed(untpd.RefinedTypeTree(tyconSplice, List(untpd.TypeDef(tpnme.Self, tparamSplice))))
+      typed(untpd.RefinedTypeTree(spliced(tycon), List(untpd.TypeDef(tpnme.Self, tparamSplice))))
     else
       def selfNote =
         if Feature.enabled(modularity) then

tests/pos/i20901/Foo.scala

@@ -0,0 +1,6 @@
+//> using options -Ytest-pickler-check
+
+import reflect.ClassTag
+
+class Foo:
+  def mkArray[T: ClassTag] = ???

tests/pos/i20901/Foo.tastycheck

@@ -0,0 +1,124 @@
+Header:
+  version: <elided>
+  tooling: <elided>
+     UUID: <elided>
+
+Names (276 bytes, starting from <elided base index>):
+     0: ASTs
+     1: <empty>
+     2: scala
+     3: reflect
+     4: scala[Qualified . reflect]
+     5: ClassTag
+     6: Foo
+     7: <init>
+     8: java
+     9: lang
+    10: java[Qualified . lang]
+    11: Object
+    12: java[Qualified . lang][Qualified . Object]
+    13: <init>[Signed Signature(List(),java.lang.Object) @<init>]
+    14: Unit
+    15: mkArray
+    16: T
+    17: Nothing
+    18: Any
+    19: evidence$
+    20: [Unique evidence$ 1]
+    21: ???
+    22: Predef
+    23: SourceFile
+    24: annotation
+    25: scala[Qualified . annotation]
+    26: internal
+    27: scala[Qualified . annotation][Qualified . internal]
+    28: scala[Qualified . annotation][Qualified . internal][Qualified . SourceFile]
+    29: String
+    30: java[Qualified . lang][Qualified . String]
+    31: <init>[Signed Signature(List(java.lang.String),scala.annotation.internal.SourceFile) @<init>]
+    32: <elided source file name>
+    33: Positions
+    34: Comments
+    35: Attributes
+
+Trees (94 bytes, starting from <elided base index>):
+     0: PACKAGE(92)
+     2:   TERMREFpkg 1 [<empty>]
+     4:   IMPORT(4)
+     6:     TERMREFpkg 4 [scala[Qualified . reflect]]
+     8:     IMPORTED 5 [ClassTag]
+    10:   TYPEDEF(82) 6 [Foo]
+    13:     TEMPLATE(61)
+    15:       APPLY(10)
+    17:         SELECTin(8) 13 [<init>[Signed Signature(List(),java.lang.Object) @<init>]]
+    20:           NEW
+    21:             TYPEREF 11 [Object]
+    23:               TERMREFpkg 10 [java[Qualified . lang]]
+    25:           SHAREDtype 21
+    27:       DEFDEF(7) 7 [<init>]
+    30:         EMPTYCLAUSE
+    31:         TYPEREF 14 [Unit]
+    33:           TERMREFpkg 2 [scala]
+    35:         STABLE
+    36:       DEFDEF(38) 15 [mkArray]
+    39:         TYPEPARAM(11) 16 [T]
+    42:           TYPEBOUNDStpt(8)
+    44:             TYPEREF 17 [Nothing]
+    46:               SHAREDtype 33
+    48:             TYPEREF 18 [Any]
+    50:               SHAREDtype 33
+    52:         PARAM(14) 20 [[Unique evidence$ 1]]
+    55:           APPLIEDtpt(10)
+    57:             IDENTtpt 5 [ClassTag]
+    59:               TYPEREF 5 [ClassTag]
+    61:                 SHAREDtype 6
+    63:             IDENTtpt 16 [T]
+    65:               TYPEREFdirect 39
+    67:           IMPLICIT
+    68:         SHAREDtype 44
+    70:         TERMREF 21 [???]
+    72:           TERMREF 22 [Predef]
+    74:             SHAREDtype 33
+    76:     ANNOTATION(16)
+    78:       TYPEREF 23 [SourceFile]
+    80:         TERMREFpkg 27 [scala[Qualified . annotation][Qualified . internal]]
+    82:       APPLY(10)
+    84:         SELECTin(6) 31 [<init>[Signed Signature(List(java.lang.String),scala.annotation.internal.SourceFile) @<init>]]
+    87:           NEW
+    88:             SHAREDtype 78
+    90:           SHAREDtype 78
+    92:         STRINGconst 32 [<elided source file name>]
+    94:
+
+Positions (72 bytes, starting from <elided base index>):
+  lines: 7
+  line sizes:
+     38, 0, 23, 0, 10, 32, 0
+  positions:
+     0: 40 .. 108
+     4: 40 .. 63
+     6: 47 .. 54
+     8: 55 .. 63
+    10: 65 .. 108
+    13: 78 .. 108
+    21: 71 .. 71
+    27: 78 .. 78
+    31: 78 .. 78
+    36: 78 .. 108
+    39: 90 .. 101
+    44: 93 .. 93
+    48: 93 .. 93
+    52: 93 .. 101
+    57: 93 .. 101
+    63: 93 .. 101
+    68: 102 .. 102
+    70: 105 .. 108
+    82: 65 .. 108
+    88: 65 .. 65
+    92: 65 .. 65
+
+  source paths:
+     0: 32 [<elided source file name>]
+
+Attributes (2 bytes, starting from <elided base index>):
+  SOURCEFILEattr 32 [<elided source file name>]