--- /dev/null
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !go1.12
+
+package span
+
+import (
+ "go/token"
+)
+
+// lineStart is the pre-Go 1.12 version of (*token.File).LineStart. For Go
+// versions <= 1.11, we borrow logic from the analysisutil package.
+// TODO(rstambler): Delete this file when we no longer support Go 1.11.
+func lineStart(f *token.File, line int) token.Pos {
+ // Use binary search to find the start offset of this line.
+
+ min := 0 // inclusive
+ max := f.Size() // exclusive
+ for {
+ offset := (min + max) / 2
+ pos := f.Pos(offset)
+ posn := f.Position(pos)
+ if posn.Line == line {
+ return pos - (token.Pos(posn.Column) - 1)
+ }
+
+ if min+1 >= max {
+ return token.NoPos
+ }
+
+ if posn.Line < line {
+ min = offset
+ } else {
+ max = offset
+ }
+ }
+}