4 files changed, 32 insertions, 1 deletions
diff --git a/src/main/antlr4/FIRRTL.g4 b/src/main/antlr4/FIRRTL.g4
index d40c6560..10a87c9e 100644
--- a/src/main/antlr4/FIRRTL.g4
+++ b/src/main/antlr4/FIRRTL.g4
@@ -29,7 +29,16 @@ import firrtl.LexerHelper;
 
 // Does there have to be at least one module?
 circuit
-  : 'circuit' id ':' info? INDENT module* DEDENT EOF
+  : version? NEWLINE* 'circuit' id ':' info? INDENT module* DEDENT EOF
+  ;
+
+version
+  : 'FIRRTL' 'version' semver NEWLINE
+  ;
+
+// Due to lexer problems, something like 1.1.0 is lexed as DoubleLit '.' UnsignedInt
+semver
+  : DoubleLit '.' UnsignedInt
   ;
 
 module
diff --git a/src/main/scala/firrtl/Parser.scala b/src/main/scala/firrtl/Parser.scala
index bb93511c..b2d97e86 100644
--- a/src/main/scala/firrtl/Parser.scala
+++ b/src/main/scala/firrtl/Parser.scala
@@ -17,6 +17,7 @@ case class ParameterRedefinedException(message: String) extends ParserException(
 case class InvalidStringLitException(message: String) extends ParserException(message)
 case class InvalidEscapeCharException(message: String) extends ParserException(message)
 case class SyntaxErrorsException(message: String) extends ParserException(message)
+case class UnsupportedVersionException(message: String) extends ParserException(message)
 
 object Parser extends LazyLogging {
 
diff --git a/src/main/scala/firrtl/ir/Serializer.scala b/src/main/scala/firrtl/ir/Serializer.scala
index f5457dea..0666a4b1 100644
--- a/src/main/scala/firrtl/ir/Serializer.scala
+++ b/src/main/scala/firrtl/ir/Serializer.scala
@@ -6,10 +6,19 @@ import firrtl.Utils
 import firrtl.backends.experimental.smt.random.DefRandom
 import firrtl.constraint.Constraint
 
+case class Version(major: Int, minor: Int, patch: Int) {
+  def serialize: String = s"$major.$minor.$patch"
+  def incompatible(that: Version): Boolean =
+    this.major > that.major || (this.major == that.major && this.minor > that.minor)
+}
+
 object Serializer {
   val NewLine = '\n'
   val Indent = "  "
 
+  // The version supported by the serializer.
+  val version = Version(1, 1, 0)
+
   /** Converts a `FirrtlNode` into its string representation with
     * default indentation.
     */
@@ -254,6 +263,7 @@ object Serializer {
 
   private def s(node: Circuit)(implicit b: StringBuilder, indent: Int): Unit = node match {
     case Circuit(info, modules, main) =>
+      b ++= s"FIRRTL version ${version.serialize}\n"
       b ++= "circuit "; b ++= main; b ++= " :"; s(info)
       if (modules.nonEmpty) {
         newLineNoIndent(); s(modules.head)(b, indent + 1)
diff --git a/src/main/scala/firrtl/parser/Listener.scala b/src/main/scala/firrtl/parser/Listener.scala
index ffaa22b2..1f6692ca 100644
--- a/src/main/scala/firrtl/parser/Listener.scala
+++ b/src/main/scala/firrtl/parser/Listener.scala
@@ -6,6 +6,7 @@ import firrtl.antlr.{FIRRTLParser, _}
 import firrtl.Visitor
 import firrtl.Parser.InfoMode
 import firrtl.ir._
+import firrtl.UnsupportedVersionException
 
 import scala.collection.mutable
 import scala.concurrent.{Await, Future}
@@ -25,6 +26,16 @@ private[firrtl] class Listener(infoMode: InfoMode) extends FIRRTLBaseListener {
   }
 
   override def exitCircuit(ctx: FIRRTLParser.CircuitContext): Unit = {
+    if (ctx.version != null) {
+      val version = ctx.version.semver.getText
+      val parts = version.split("\\.")
+      val (major, minor, patch) = (parts(0).toInt, parts(1).toInt, parts(2).toInt)
+      if (Version(major, minor, patch).incompatible(Serializer.version)) {
+        throw new UnsupportedVersionException(
+          s"FIRRTL version ${version} is not supported (greater than ${Serializer.version.serialize})"
+        )
+      }
+    }
     info = Some(visitor.visitInfo(Option(ctx.info), ctx))
     main = Some(ctx.id.getText)
     ctx.children = null // Null out to save memory