Type inference fails with overload and record extension

[johnjcamilleri]

Originally reported by Roman Suzi in gf-dev.

When trying to extend a record produced by an overloaded oper, type inference fails:

resource TestRes = {
  oper
    Rec: Type = {
      a, b: Str ;
    } ;

    mkRec1: Str -> Rec = \a -> { a = a; b = a } ;
    mkRec2: Str -> Str -> Rec = \a,b -> { a = a; b = b } ;
    
    mkRec = overload {
      mkRec: Str -> Rec = mkRec1 ;
      mkRec: Str -> Str -> Rec = mkRec2 ;
    } ;
    
    r1: Rec = mkRec1 "A" ** {a = "X"} ; -- ok
    r2: Rec = mkRec2 "A" "B" ** {a = "X"} ; -- ok

    r3: Rec = mkRec "A" "B" ; -- ok
    r4: Rec = mkRec "A" "B" ** {a = "X"} ; -- fails
    r5: Rec =
      let r: Rec = mkRec "A" "B"
      in  r ** {a = "X"} ; -- ok
    r6: Rec = <mkRec "A" "B": Rec> ** {a = "X"} ; -- fails
}

Error for r4:

 TestRes.gf:19:
   Happened in operation r4
    no overload instance of TestRes.mkRec
    with value type {b : Str}
    for argument list
      Str Str
    among alternatives
      Str
      Str Str

Error for r6:

 TestRes.gf:23:
   Happened in operation r6
    no overload instance of TestRes.mkRec
    with value type {a : Str; b : Str}
    for argument list
      Str Str
    among alternatives
      Str
      Str Str

[johnjcamilleri]

Another thing that works:

  oper
    wrap: Rec -> Rec = \r -> r ;
    r7: Rec = wrap (mkRec "A" "B") ** {a = "X"} ; -- ok