fixes #10053 (#11951)

compiler/ccgexprs.nim

@@ -825,7 +825,8 @@ proc genFieldCheck(p: BProc, e: PNode, obj: Rope, field: PSym) =
     v.r.add(".")
     v.r.add(disc.sym.loc.r)
     genInExprAux(p, it, u, v, test)
-    let strLit = genStringLiteral(p.module, newStrNode(nkStrLit, field.name.s))
+    let msg = genFieldError(field, disc.sym)
+    let strLit = genStringLiteral(p.module, newStrNode(nkStrLit, msg))
     if op.magic == mNot:
       linefmt(p, cpsStmts,
               "if ($1) #raiseFieldError($2);$n",

compiler/jsgen.nim

@@ -1157,9 +1157,10 @@ proc genCheckedFieldOp(p: PProc, n: PNode, addrTyp: PType, r: var TCompRes) =
 
   useMagic(p, "raiseFieldError")
   useMagic(p, "makeNimstrLit")
+  let msg = genFieldError(field, disc)
   lineF(p, "if ($1[$2.$3]$4undefined) { raiseFieldError(makeNimstrLit($5)); }$n",
     setx.res, tmp, disc.loc.r, if negCheck: ~"!==" else: ~"===",
-    makeJSString(field.name.s))
+    makeJSString(msg))
 
   if addrTyp != nil and mapType(p, addrTyp) == etyBaseIndex:
     r.typ = etyBaseIndex

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

lib/system/chcks.nim

@@ -26,7 +26,7 @@ proc raiseIndexError() {.compilerproc, noinline.} =
   sysFatal(IndexError, "index out of bounds")
 
 proc raiseFieldError(f: string) {.compilerproc, noinline.} =
-  sysFatal(FieldError, f, " is not accessible")
+  sysFatal(FieldError, f)
 
 proc chckIndx(i, a, b: int): int =
   if i >= a and i <= b:

lib/system/jssys.nim

@@ -163,7 +163,7 @@ proc raiseIndexError(i, a, b: int) {.compilerproc, noreturn.} =
   raise newException(IndexError, formatErrorIndexBound(int(i), int(a), int(b)))
 
 proc raiseFieldError(f: string) {.compilerproc, noreturn.} =
-  raise newException(FieldError, f & " is not accessible")
+  raise newException(FieldError, f)
 
 proc setConstr() {.varargs, asmNoStackFrame, compilerproc.} =
   asm """