Based on Ivy's behavior, bringing back approximation

I assumed 1.1+ should be treated as 1.+, but it seems like Ivy treats
it more as “any version that starts with 1.1” including 1.10.
Josh’s original implementation approximates this by making ranges for
multiple digits, 1.1~1.2, 1.10~1.20, etc.

ivy/src/main/scala/sbt/MakePom.scala

@@ -210,17 +210,19 @@ class MakePom(val log: Logger) {
     }
     val startSym = Set(']', '[', '(')
     val stopSym = Set(']', '[', ')')
-    val PlusPattern = """(.+)(\.\d*\+)""".r
+    val DotPlusPattern = """(.+)\.\+""".r
+    val DotNumPlusPattern = """(.+)\.(\d+)\+""".r
+    val NumPlusPattern = """(\d+)\+""".r
+    val maxDigit = 5
     try {
       revision match {
-        case PlusPattern(base, tail) => plusRange(base)
-        // There's no direct translation for a dynamic revision like "1+".
-        // This is likely the build user misunderstanding the meaning of "+",
-        // which means pick the latest in the version segment.
-        // So if someone wanted (1.0 <= x), then it should be "[1.0)" or "1.+".
-        // Technically speaking, "1+" should convert to "LATEST",
-        // but that seems to be deprecated now, so picking the minimum version "0".
-        case rev if rev endsWith "+" => "[0,)"
+        case "+"                           => "[0,)"
+        case DotPlusPattern(base)          => plusRange(base)
+        // This is a heuristic.  Maven just doesn't support Ivy's notions of 1+, so
+        // we assume version ranges never go beyond 5 siginificant digits.
+        case NumPlusPattern(tail)          => (0 until maxDigit).map(plusRange(tail, _)).mkString(",")
+        case DotNumPlusPattern(base, tail) => (0 until maxDigit).map(plusRange(base + "." + tail, _)).mkString(",")
+        case rev if rev endsWith "+"       => sys.error(s"dynamic revision '$rev' cannot be translated to POM")
         case rev if startSym(rev(0)) && stopSym(rev(rev.length - 1)) =>
           val start = rev(0)
           val stop = rev(rev.length - 1)

ivy/src/test/scala/MakePomSpec.scala

@@ -47,14 +47,27 @@ class MakePomSpec extends Specification {
     ${convertTo("12.31.42.+", "[12.31.42,12.31.43)")}
 
   1.1+ should
-    ${convertTo("1.1+", "[1,2)")}
+    ${convertTo("1.1+", "[1.1,1.2),[1.10,1.20),[1.100,1.200),[1.1000,1.2000),[1.10000,1.20000)")}
 
   1+ should
-    ${convertTo("1+", "[0,)")}
+    ${convertTo("1+", "[1,2),[10,20),[100,200),[1000,2000),[10000,20000)")}
+
+  + should
+    ${convertTo("+", "[0,)")}
+
+  foo+ should
+    ${beParsedAsError("foo+")}
                                                                 """
 
   val mp = new MakePom(ConsoleLogger())
   def convertTo(s: String, expected: String) =
     mp.makeDependencyVersion(s) must_== expected
+  def beParsedAsError(s: String) =
+    try {
+      mp.makeDependencyVersion(s)
+      failure
+    } catch {
+      case e: Throwable => success
+    }
 }