Allow nested digit fields in subfield expressions

Workaround for #470. This allows parsing DoubleLits in subfield
expressions.

3 files changed, 33 insertions, 1 deletions

diff --git a/src/main/antlr4/FIRRTL.g4 b/src/main/antlr4/FIRRTL.g4
index 69b7ba5d..cdec7260 100644
--- a/src/main/antlr4/FIRRTL.g4
+++ b/src/main/antlr4/FIRRTL.g4
@@ -164,6 +164,7 @@ exp
   | 'SInt' ('<' intLit '>')? '(' intLit ')'
   | id    // Ref
   | exp '.' fieldId
+  | exp '.' DoubleLit // TODO Workaround for #470
   | exp '[' intLit ']'
   | exp '[' exp ']'
   | 'mux(' exp exp exp ')'
diff --git a/src/main/scala/firrtl/Visitor.scala b/src/main/scala/firrtl/Visitor.scala
index 2db46271..73555a37 100644
--- a/src/main/scala/firrtl/Visitor.scala
+++ b/src/main/scala/firrtl/Visitor.scala
@@ -17,6 +17,12 @@ class Visitor(infoMode: InfoMode) extends FIRRTLBaseVisitor[FirrtlNode] {
   // Strip file path
   private def stripPath(filename: String) = filename.drop(filename.lastIndexOf("/") + 1)
 
+  // Check if identifier is made of legal characters
+  private def legalId(id: String) = {
+    val legalChars = ('A' to 'Z').toSet ++ ('a' to 'z').toSet ++ ('0' to '9').toSet ++ Set('_', '$')
+    id forall legalChars
+  }
+
   def visit[FirrtlNode](ctx: FIRRTLParser.CircuitContext): Circuit = visitCircuit(ctx)
 
   //  These regex have to change if grammar changes
@@ -315,7 +321,19 @@ class Visitor(infoMode: InfoMode) extends FIRRTLBaseVisitor[FirrtlNode] {
         case "mux(" => Mux(visitExp(ctx.exp(0)), visitExp(ctx.exp(1)), visitExp(ctx.exp(2)), UnknownType)
         case _ =>
           ctx.getChild(1).getText match {
-            case "." => new SubField(visitExp(ctx.exp(0)), ctx.fieldId.getText, UnknownType)
+            case "." =>
+              val expr1 = visitExp(ctx.exp(0))
+              // TODO Workaround for #470
+              if (ctx.fieldId == null) {
+                ctx.DoubleLit.getText.split('.') match {
+                  case Array(a, b) if legalId(a) && legalId(b) =>
+                    val inner = new SubField(expr1, a, UnknownType)
+                    new SubField(inner, b, UnknownType)
+                  case Array() => throw new ParserException(s"Illegal Expression at ${ctx.getText}")
+                }
+              } else {
+                new SubField(expr1, ctx.fieldId.getText, UnknownType)
+              }
             case "[" => if (ctx.exp(1) == null)
               new SubIndex(visitExp(ctx.exp(0)), string2Int(ctx.intLit(0).getText), UnknownType)
             else new SubAccess(visitExp(ctx.exp(0)), visitExp(ctx.exp(1)), UnknownType)
diff --git a/src/test/scala/firrtlTests/ParserSpec.scala b/src/test/scala/firrtlTests/ParserSpec.scala
index a1f14c8e..cd9bfb40 100644
--- a/src/test/scala/firrtlTests/ParserSpec.scala
+++ b/src/test/scala/firrtlTests/ParserSpec.scala
@@ -93,6 +93,19 @@ class ParserSpec extends FirrtlFlatSpec {
     }
   }
 
+  // ********** Digits as Fields **********
+  "Digits" should "be legal fields in bundles and in subexpressions" in {
+    val input = """
+      |circuit Test :
+      |  module Test :
+      |    input in : { 0 : { 0 : UInt<32>, flip 1 : UInt<32> } }
+      |    input in2 : { 4 : { 23 : { foo : UInt<32>, bar : { flip 123 : UInt<32> } } } }
+      |    in.0.1 <= in.0.0
+      |    in2.4.23.bar.123 <= in2.4.23.foo
+      """.stripMargin
+    firrtl.Parser.parse(input split "\n")
+  }
+
   // ********** Doubles as parameters **********
   "Doubles" should "be legal parameters for extmodules" in {
     val nums = Seq("1.0", "7.6", "3.00004", "1.0E10", "1.0023E-17")