Give a nice error when no command is given

compiler/msgs.nim

@@ -82,7 +82,7 @@ type
     errArrayExpectsTwoTypeParams, errInvalidVisibilityX, errInitHereNotAllowed,
     errXCannotBeAssignedTo, errIteratorNotAllowed, errXNeedsReturnType,
     errNoReturnTypeDeclared,
-    errInvalidCommandX, errXOnlyAtModuleScope,
+    errNoCommand, errInvalidCommandX, errXOnlyAtModuleScope,
     errXNeedsParamObjectType,
     errTemplateInstantiationTooNested, errInstantiationFrom,
     errInvalidIndexValueForTuple, errCommandExpectsFilename,
@@ -316,6 +316,7 @@ const
     errIteratorNotAllowed: "iterators can only be defined at the module\'s top level",
     errXNeedsReturnType: "$1 needs a return type",
     errNoReturnTypeDeclared: "no return type declared",
+    errNoCommand: "no command given",
     errInvalidCommandX: "invalid command: \'$1\'",
     errXOnlyAtModuleScope: "\'$1\' is only allowed at top level",
     errXNeedsParamObjectType: "'$1' needs a parameter that has an object type",

compiler/nim.nim

@@ -58,6 +58,8 @@ proc handleCmdLine() =
     # command line can overwite the config file's settings
     extccomp.initVars()
     processCmdLine(passCmd2, "")
+    if options.command == "":
+      rawMessage(errNoCommand, command)
     mainCommand()
     if optHints in gOptions and hintGCStats in gNotes: echo(GC_getStatistics())
     #echo(GC_getStatistics())