Implemented compileOption for experimental to test if a feature i… (#23933)

…s enabled at compile time.

#8644 This doesn't handle the case if `{.push experimental.}` is used,
but at least we can test if a feature was enabled globally.

compiler/commands.nim

@@ -24,7 +24,7 @@ bootSwitch(usedMarkAndSweep, defined(gcmarkandsweep), "--gc:markAndSweep")
 bootSwitch(usedGoGC, defined(gogc), "--gc:go")
 bootSwitch(usedNoGC, defined(nogc), "--gc:none")
 
-import std/[setutils, os, strutils, parseutils, parseopt, sequtils, strtabs]
+import std/[setutils, os, strutils, parseutils, parseopt, sequtils, strtabs, enumutils]
 import
   msgs, options, nversion, condsyms, extccomp, platform,
   wordrecg, nimblecmd, lineinfos, pathutils
@@ -248,6 +248,7 @@ const
   errNoneSpeedOrSizeExpectedButXFound = "'none', 'speed' or 'size' expected, but '$1' found"
   errGuiConsoleOrLibExpectedButXFound = "'gui', 'console', 'lib' or 'staticlib' expected, but '$1' found"
   errInvalidExceptionSystem = "'goto', 'setjmp', 'cpp' or 'quirky' expected, but '$1' found"
+  errInvalidFeatureButXFound = Feature.toSeq.map(proc(val:Feature): string = "'$1'" % $val).join(", ") & " expected, but '$1' found"
 
 template warningOptionNoop(switch: string) =
   warningDeprecated(conf, info, "'$#' is deprecated, now a noop" % switch)
@@ -303,6 +304,12 @@ proc testCompileOptionArg*(conf: ConfigRef; switch, arg: string, info: TLineInfo
     else:
       result = false
       localError(conf, info, errInvalidExceptionSystem % arg)
+  of "experimental":
+    try:
+      result = conf.features.contains parseEnum[Feature](arg)
+    except ValueError:
+      result = false
+      localError(conf, info, errInvalidFeatureButXFound % arg)
   else:
     result = false
     invalidCmdLineOption(conf, passCmd1, switch, info)