Fix line and column number reporting for Windows newlines (#282)

Previous implementation of `lineNumberLookup` only worked for single
`\n` or `\r` newlines. This PR fixes it so it also works for `\n\r` or
`\r\n` newlines and adds some basic tests

fastparse/src/fastparse/internal/Util.scala

@@ -47,30 +47,31 @@ object Util {
     rec(0)
   }
   def lineNumberLookup(data: String): Array[Int] = {
-    val lineStarts = new ArrayBuffer[Int]()
+    val lineStarts = ArrayBuffer[Int](0)
     var i = 0
     var col = 1
-    var cr = false
-    var prev: Character = null
+    // Stores the previous char we saw, or -1 if we just saw a \r\n or \n\r pair
+    var state: Int = 0
     while (i < data.length){
       val char = data(i)
-      if (char == '\r') {
-        if (prev != '\n' && col == 1) lineStarts.append(i)
-        col = 1
-        cr = true
-      }else if (char == '\n') {
-        if (prev != '\r' && col == 1) lineStarts.append(i)
+      if (char == '\r' && state == '\n' || char == '\n' && state == '\r'){
+        col += 1
+        state = -1
+      } else if (state == '\r' || state == '\n' || state == -1) {
+        lineStarts.append(i)
         col = 1
-        cr = false
+        state = char
       }else{
-        if (col == 1) lineStarts.append(i)
         col += 1
-        cr = false
+        state = char
       }
-      prev = char
+
       i += 1
     }
-    if (col == 1) lineStarts.append(i)
+
+    if (state == '\r' || state == '\n' || state == -1) {
+      lineStarts.append(i)
+    }
 
     lineStarts.toArray
   }

fastparse/test/src/fastparse/UtilTests.scala

@@ -42,5 +42,56 @@ object UtilTests extends TestSuite {
       )
       assert(pretties == expected)
     }
+
+    test("unix"){
+      val txt = Array(
+        "def myScalaVersion = \"2.13.2\"\n",
+        "\n",
+        "//hello\n",
+        "println(doesntExis})"
+      ).mkString
+
+      val lineStarts = fastparse.internal.Util.lineNumberLookup(txt).toList
+
+      assert(lineStarts == List(0, 30, 31, 39))
+    }
+
+    test("carriageReturnOnly") {
+      val txt = Array(
+        "def myScalaVersion = \"2.13.2\"\r",
+        "\r",
+        "//hello\r",
+        "println(doesntExis})"
+      ).mkString
+
+      val lineStarts = fastparse.internal.Util.lineNumberLookup(txt).toList
+
+      assert(lineStarts == List(0, 30, 31, 39))
+    }
+
+    test("windows"){
+      val txt = Array(
+        "def myScalaVersion = \"2.13.2\"\r\n",
+        "\r\n",
+        "//hello\r\n",
+        "println(doesntExis})"
+      ).mkString
+
+      val lineStarts = fastparse.internal.Util.lineNumberLookup(txt).toList
+
+      assert(lineStarts == List(0, 31, 33, 42))
+    }
+    test("reverseWindows"){
+      val txt = Array(
+        "def myScalaVersion = \"2.13.2\"\n\r",
+        "\n\r",
+        "//hello\n\r",
+        "println(doesntExis})"
+      ).mkString
+
+      val lineStarts = fastparse.internal.Util.lineNumberLookup(txt).toList
+
+      assert(lineStarts == List(0, 31, 33, 42))
+    }
   }
 }