Show (short) list of possible enum values when an invalid value is encountered (resolves #1318)

All enum errors have (hopefully) been changed to a luax_enumerror, which has a
fixed error message. If additionally a list of valid options is passed, it
lists that in the error message. For every enum error with few options I've
implemented this using a getConstants call.

This solution has been designed specifically to reduce the number of template
instantiations (as I've been told that was a concern). All new template code
happens in places where there already was an instantiation of the relevant
StringMap. Of course there is still std::vector<std::string>...

--HG--
branch : minor

src/modules/image/ImageData.cpp

@@ -502,6 +502,11 @@ bool ImageData::getConstant(FormatHandler::EncodedFormat in, const char *&out)
 	return encodedFormats.find(in, out);
 }
 
+std::vector<std::string> ImageData::getConstants(FormatHandler::EncodedFormat)
+{
+	return encodedFormats.getNames();
+}
+
 StringMap<FormatHandler::EncodedFormat, FormatHandler::ENCODED_MAX_ENUM>::Entry ImageData::encodedFormatEntries[] =
 {
 	{"tga", FormatHandler::ENCODED_TGA},

src/modules/image/ImageData.h

@@ -117,6 +117,7 @@ public:
 
 	static bool getConstant(const char *in, FormatHandler::EncodedFormat &out);
 	static bool getConstant(FormatHandler::EncodedFormat in, const char *&out);
+	static std::vector<std::string> getConstants(FormatHandler::EncodedFormat);
 
 private:
 

src/modules/image/wrap_Image.cpp

@@ -50,7 +50,7 @@ int w_newImageData(lua_State *L)
 		{
 			const char *fstr = luaL_checkstring(L, 3);
 			if (!getConstant(fstr, format))
-				return luaL_error(L, "Invalid pixel format: %s", fstr);
+				return luax_enumerror(L, "pixel format", fstr);
 		}
 
 		size_t numbytes = 0;

src/modules/image/wrap_ImageData.cpp

@@ -265,7 +265,7 @@ int w_ImageData_encode(lua_State *L)
 	FormatHandler::EncodedFormat format;
 	const char *fmt = luaL_checkstring(L, 2);
 	if (!ImageData::getConstant(fmt, format))
-		return luaL_error(L, "Invalid encoded image format '%s'.", fmt);
+		return luax_enumerror(L, "encoded image format", ImageData::getConstants(format), fmt);
 
 	bool hasfilename = false;