fixes #11675

compiler/options.nim

@@ -110,7 +110,7 @@ type
     cmdJsonScript             # compile a .json build file
   TStringSeq* = seq[string]
   TGCMode* = enum             # the selected GC
-    gcNone, gcBoehm, gcRegions, gcMarkAndSweep, gcDestructors,
+    gcUnselected, gcNone, gcBoehm, gcRegions, gcMarkAndSweep, gcDestructors,
     gcRefc, gcV2, gcGo
     # gcRefc and the GCs that follow it use a write barrier,
     # as far as usesWriteBarrier() is concerned

compiler/scriptconfig.nim

@@ -214,6 +214,12 @@ proc runNimScript*(cache: IdentCache; scriptName: AbsoluteFile;
 
   conf.searchPaths.add(conf.libpath)
 
+  let oldGlobalOptions = conf.globalOptions
+  let oldSelectedGC = conf.selectedGC
+  undefSymbol(conf.symbols, "nimv2")
+  conf.globalOptions.excl optNimV2
+  conf.selectedGC = gcUnselected
+
   var m = graph.makeModule(scriptName)
   incl(m.flags, sfMainModule)
   graph.vm = setupVM(m, cache, scriptName.string, graph)
@@ -221,6 +227,14 @@ proc runNimScript*(cache: IdentCache; scriptName: AbsoluteFile;
   graph.compileSystemModule() # TODO: see why this unsets hintConf in conf.notes
   discard graph.processModule(m, llStreamOpen(scriptName, fmRead))
 
+  # watch out, "newruntime" can be set within NimScript itself and then we need
+  # to remember this:
+  if optNimV2 in oldGlobalOptions:
+    conf.globalOptions.incl optNimV2
+    defineSymbol(conf.symbols, "nimv2")
+  if conf.selectedGC == gcUnselected:
+    conf.selectedGC = oldSelectedGC
+
   # ensure we load 'system.nim' again for the real non-config stuff!
   resetSystemArtifacts(graph)
   # do not remove the defined symbols