fixes #10053 (#11951)

compiler/renderer.nim

@@ -1575,3 +1575,15 @@ proc getTokSym*(r: TSrcGen): PSym =
     result = r.tokens[r.idx-1].sym
   else:
     result = nil
+
+proc quoteExpr*(a: string): string {.inline.} =
+  ## can be used for quoting expressions in error msgs.
+  "'" & a & "'"
+
+proc genFieldError*(field: PSym, disc: PSym): string =
+  ## this needs to be in a module accessible by jsgen, ccgexprs, and vm to
+  ## provide this error msg FieldError; msgs would be better but it does not
+  ## import ast
+  result = field.name.s.quoteExpr & " is not accessible using discriminant " &
+    disc.name.s.quoteExpr & " of type " &
+    disc.owner.name.s.quoteExpr