Fix MultiInfo parser + serialization bug (#2265)

* Restore parsed MultiInfo structure in firrtl parser

* Change erroneous expected output in InfoSpec test

FileInfo compression sorts the outputted entries alphabetically, but
this test did not reflect that fact

* Fix typo in comment

* Add unit tests for file locator parsing

* Fix syntax issues and typos

* More redundant braces removed

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

src/main/scala/firrtl/Visitor.scala

@@ -58,6 +58,51 @@ class Visitor(infoMode: InfoMode) extends AbstractParseTreeVisitor[FirrtlNode] w
   private def string2Int(s: String): Int = string2BigInt(s).toInt
 
   private def visitInfo(ctx: Option[InfoContext], parentCtx: ParserRuleContext): Info = {
+    // Convert a compressed FileInfo string into either into a singular FileInfo or a MultiInfo
+    // consisting of several FileInfos
+    def parseCompressedInfo(escaped: String): Info = {
+      var out: Seq[FileInfo] = Seq()
+
+      // Regular expression to match and capture the general File.format line:col pattern.
+      // Also matches the remaining part of the string which doesn't match the expression;
+      // which will be passed directly into the output as a FileInfo.
+      val splitCompressedInfo = """([^\s:]+)((?: \d+:(?:\d+|\{\d+(?:,\d+)+\}))+)|(?:[^\s].*)""".r
+
+      // Regular expression to capture the line number and column numbers in the compressed file info pattern.
+      val splitLineDescriptors = """(\d+):((?:\d+|\{\d+(?:,\d+)+\}))""".r
+
+      // Regular expression to match against individual column numbers in each line:col or line:{col1,col2}
+      // descriptor.
+      val splitColDescriptors = """\d+""".r
+
+      val matches = splitCompressedInfo.findAllIn(escaped)
+
+      // Grab each File.format line:col token from the input string
+      splitCompressedInfo.findAllIn(escaped).matchData.foreach { info =>
+        Option(info.group(1)) match {
+          // If there were no subgroups, the regex matched against a non-conforming source locator
+          // pattern, so do not process it
+          case None => out = out :+ ir.FileInfo.fromEscaped(info.toString)
+          case Some(file) =>
+            val lineDescriptors = info.group(2)
+            // Grab each line:col values from the separated (compressed) FileInfo.
+            splitLineDescriptors.findAllIn(lineDescriptors).matchData.foreach { lineDescriptor =>
+              val line = lineDescriptor.group(1)
+              val cols = lineDescriptor.group(2)
+              splitColDescriptors.findAllIn(cols).matchData.foreach {
+                // Use all the necessary info to generate normal uncompressed FileInfos
+                col => out = out :+ ir.FileInfo.fromEscaped(s"$file $line:$col")
+              }
+            }
+        }
+      }
+
+      out.size match {
+        case 0 => NoInfo
+        case 1 => out.head
+        case _ => new MultiInfo(out)
+      }
+    }
     def genInfo(filename: String): String =
       stripPath(filename) + " " + parentCtx.getStart.getLine + ":" +
         parentCtx.getStart.getCharPositionInLine
@@ -68,11 +113,11 @@ class Visitor(infoMode: InfoMode) extends AbstractParseTreeVisitor[FirrtlNode] w
     infoMode match {
       case UseInfo =>
         if (useInfo.length == 0) NoInfo
-        else ir.FileInfo.fromEscaped(useInfo)
+        else parseCompressedInfo(useInfo)
       case AppendInfo(filename) if (useInfo.length == 0) =>
         ir.FileInfo.fromEscaped(genInfo(filename))
       case AppendInfo(filename) =>
-        val useFileInfo = ir.FileInfo.fromEscaped(useInfo)
+        val useFileInfo = parseCompressedInfo(useInfo)
         val newFileInfo = ir.FileInfo.fromEscaped(genInfo(filename))
         ir.MultiInfo(useFileInfo, newFileInfo)
       case GenInfo(filename) =>

src/test/scala/firrtlTests/InfoSpec.scala

@@ -288,7 +288,7 @@ class InfoSpec extends FirrtlFlatSpec with FirrtlMatchers {
       "  wire [31:0] a = c ? b : d; // @[A 1:{2,3,4} B 2:3 4:5]"
     )
     result("A 2:3", "B 1:{2,3,4}", "C 4:5") should containLine(
-      "  wire [31:0] a = c ? b : d; // @[B 1:{2,3,4} A 2:3 C 4:5]"
+      "  wire [31:0] a = c ? b : d; // @[A 2:3 B 1:{2,3,4} C 4:5]"
     )
   }
 
@@ -321,4 +321,17 @@ class InfoSpec extends FirrtlFlatSpec with FirrtlMatchers {
     for (line <- check)
       result should containLine(line)
   }
+
+  "Source Locators" should "not lose information when going through serialization + parsing" in {
+    def check(info: ir.Info): Unit = {
+      assert(Parser.parseInfo(info.serialize) == info)
+    }
+
+    check(ir.NoInfo)
+    check(ir.FileInfo("B"))
+    check(ir.FileInfo("A 4:5"))
+    check(ir.FileInfo("A 4:6"))
+    check(ir.MultiInfo(ir.FileInfo("A 4:5"), ir.FileInfo("B 5:5")))
+    check(ir.MultiInfo(ir.FileInfo("A 4:5"), ir.FileInfo("A 5:5")))
+  }
 }