fix #17853 (ascii message separator broke json nim dump) (#17887)

compiler/main.nim

@@ -349,7 +349,8 @@ proc mainCommand*(graph: ModuleGraph) =
         (key: "warnings", val: warnings),
       ]
 
-      msgWriteln(conf, $dumpdata, {msgStdout, msgSkipHook})
+      msgWriteln(conf, $dumpdata, {msgStdout, msgSkipHook, msgNoUnitSep})
+        # `msgNoUnitSep` to avoid generating invalid json, refs bug #17853
     else:
       msgWriteln(conf, "-- list of currently defined symbols --",
                  {msgStdout, msgSkipHook, msgNoUnitSep})

compiler/msgs.nim

@@ -291,6 +291,7 @@ proc `??`* (conf: ConfigRef; info: TLineInfo, filename: string): bool =
 
 const
   UnitSep = "\31"
+    # this needs care to avoid issues similar to https://github.com/nim-lang/Nim/issues/17853
 
 type
   MsgFlag* = enum  ## flags altering msgWriteln behavior

compiler/options.nim

@@ -44,7 +44,7 @@ type                          # please make sure we have under 32 options
     optImportHidden
 
   TOptions* = set[TOption]
-  TGlobalOption* = enum       # **keep binary compatible**
+  TGlobalOption* = enum
     gloptNone, optForceFullMake,
     optWasNimscript,          # redundant with `cmdNimscript`, could be removed
     optListCmd, optCompileOnly, optNoLinking,