string to string conversion keeps the dest type (#9323)

Fixes #9322

compiler/semfold.nim

@@ -379,7 +379,7 @@ proc evalOp(m: TMagic, n, a, b, c: PNode; g: ModuleGraph): PNode =
       result = newStrNodeT(s, n, g)
     else:
       result = newStrNodeT(getStrOrChar(a), n, g)
-  of mStrToStr: result = a
+  of mStrToStr: result = newStrNodeT(getStrOrChar(a), n, g)
   of mEnumToStr: result = newStrNodeT(ordinalValToString(a, g), n, g)
   of mArrToSeq:
     result = copyTree(a)

tests/distinct/t9322.nim

@@ -0,0 +1,12 @@
+discard """
+  output: apr
+"""
+
+type Fix = distinct string
+
+proc `$`(f: Fix): string {.borrow.}
+
+proc mystr(s: string) =
+  echo s
+
+mystr($Fix("apr"))