add restrict keyword

Author: MESYETI

source/parser.d

@@ -25,7 +25,8 @@ enum NodeType {
 	String,
 	Struct,
 	Const,
-	Enum
+	Enum,
+	Restrict
 }
 
 class Node {
@@ -333,6 +334,17 @@ class EnumNode : Node {
 	}
 }
 
+class RestrictNode : Node {
+	string ver;
+
+	this(ErrorInfo perror) {
+		type  = NodeType.Restrict;
+		error = perror;
+	}
+
+	override string toString() => format("restrict %s", ver);
+}
+
 class ParserError : Exception {
 	this() {
 		super("", "", 0);
@@ -767,6 +779,17 @@ class Parser {
 		return ret;
 	}
 
+	Node ParseRestrict() {
+		auto ret = new RestrictNode(GetError());
+		parsing  = NodeType.Restrict;
+
+		Next();
+		Expect(TokenType.Identifier);
+		ret.ver = tokens[i].contents;
+
+		return ret;
+	}
+
 	Node ParseStatement() {
 		switch (tokens[i].type) {
 			case TokenType.Integer: {
@@ -787,6 +810,7 @@ class Parser {
 					case "version":    return ParseVersion();
 					case "const":      return ParseConst();
 					case "enum":       return ParseEnum();
+					case "restrict":   return ParseRestrict();
 					default: return new WordNode(GetError(), tokens[i].contents);
 				}
 			}

source/preprocessor.d

@@ -20,6 +20,7 @@ class Preprocessor {
 	string[] includeDirs;
 	string[] included;
 	string[] versions;
+	string[] restricted;
 
 	final void Error(Char, A...)(ErrorInfo error, in Char[] fmt, A args) {
 		ErrorBegin(error);
@@ -76,11 +77,30 @@ class Preprocessor {
 				case NodeType.Enable: {
 					auto node = cast(EnableNode) inode;
 
+					if (restricted.canFind(node.ver)) {
+						Error(
+							node.error, "Attempted to enable restricted version '%s'",
+							node.ver
+						);
+					}
+
 					if (!versions.canFind(node.ver)) {
 						versions ~= node.ver;
 					}
 					break;
 				}
+				case NodeType.Restrict: {
+					auto node = cast(RestrictNode) inode;
+
+					if (versions.canFind(node.ver)) {
+						Error(
+							node.error, "Restricted version '%s' is enabled", node.ver
+						);
+					}
+
+					restricted ~= node.ver;
+					break;
+				}
 				default: {
 					ret ~= inode;
 				}