Addresses issues raised on #947. Refs #800.

* Uses errGenerated instead of deprecated extending of enums.
* Reduces bloat and usefulness of end user error messages.
* Limits checks to C, Cpp and Objc targets.

compiler/msgs.nim

@@ -105,7 +105,7 @@ type
     errThreadvarCannotInit, errWrongSymbolX, errIllegalCaptureX,
     errXCannotBeClosure, errXMustBeCompileTime,
     errCannotInferTypeOfTheLiteral,
-    errBadExport, errUser
+    errUser,
     warnCannotOpenFile, 
     warnOctalEscape, warnXIsNeverRead, warnXmightNotBeenInit, 
     warnDeprecated, warnConfigDeprecated,
@@ -350,7 +350,6 @@ const
     errXCannotBeClosure: "'$1' cannot have 'closure' calling convention",
     errXMustBeCompileTime: "'$1' can only be used in compile-time context",
     errCannotInferTypeOfTheLiteral: "cannot infer the type of the $1",
-    errBadExport: "invalid exported symbol, $1",
     errUser: "$1", 
     warnCannotOpenFile: "cannot open \'$1\' [CannotOpenFile]",
     warnOctalEscape: "octal escape sequences do not exist; leading zero is ignored [OctalEscape]", 

compiler/pragmas.nim

@@ -99,25 +99,23 @@ proc makeExternImport(s: PSym, extname: string) =
 
 const invalidIdentChars = AllChars - IdentChars
 
-proc validateExternName(s: PSym, info: TLineInfo) =
+proc validateExternCName(s: PSym, info: TLineInfo) =
   ## Validates that the symbol name in s.loc.r is a valid C identifier.
   ##
   ## Valid identifiers are those alphanumeric including the underscore not
-  ## starting with a number. If the check fails, a friendly error will be
+  ## starting with a number. If the check fails, a generic error will be
   ## displayed to the user.
   let target = ropeToStr(s.loc.r)
-  if target.len < 1:
-    localError(info, errBadExport, "can't be zero length")
-  if not (target[0] in IdentStartChars):
-    localError(info, errBadExport, "'" & target & "' can't start with a number")
-  if not target.allCharsInSet(IdentChars):
-    let pos = target.find(invalidIdentChars, 1)
-    localError(info, errBadExport, "'" & target &
-      "' contains bad character at byte " & $pos)
+  if target.len < 1 or (not (target[0] in IdentStartChars)) or
+      (not target.allCharsInSet(IdentChars)):
+    localError(info, errGenerated, "invalid exported symbol")
 
 proc makeExternExport(s: PSym, extname: string, info: TLineInfo) =
   setExternName(s, extname)
-  validateExternName(s, info)
+  case gCmd
+  of cmdCompileToC, cmdCompileToCpp, cmdCompileToOC:
+    validateExternCName(s, info)
+  else: discard
   incl(s.flags, sfExportc)
 
 proc processImportCompilerProc(s: PSym, extname: string) =