Re-add AbsolutePosition.swift

Author: Harlan Haskins

tools/SwiftSyntax/AbsolutePosition.swift

@@ -0,0 +1,60 @@
+//===--------------- AbsolutePosition.swift - Source Positions ------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// An absolute position in a source file as text - the absolute utf8Offset from
+/// the start, line, and column.
+public final class AbsolutePosition {
+  public fileprivate(set) var utf8Offset: Int
+  public fileprivate(set) var line: Int
+  public fileprivate(set) var column: Int
+
+  public init(line: Int = 1, column: Int = 1, utf8Offset: Int = 0) {
+    self.line = line
+    self.column = column
+    self.utf8Offset = utf8Offset
+  }
+
+  internal func add(columns: Int) {
+    print("adding \(columns) column bytes")
+    self.column += columns
+  }
+
+  internal func add(lines: Int, size: Int) {
+    print("adding \(lines * size) line bytes")
+    self.line += lines * size
+    self.column = 1
+  }
+
+  /// Use some text as a reference for adding to the absolute position,
+  /// taking note of newlines, etc.
+  internal func add(text: String) {
+    print("adding text: \(text)")
+    for char in text {
+      switch char {
+      case "\n", "\r\n":
+        line += 1
+        column = 1
+      default:
+        column += 1
+      }
+
+      // FIXME: This is currently very wasteful, but should be fast once the
+      //        small-string optimization lands.
+      utf8Offset += String(char).utf8.count
+    }
+  }
+
+  internal func copy() -> AbsolutePosition {
+    return AbsolutePosition(line: line, column: column,
+      utf8Offset: utf8Offset)
+  }
+}