Improve pagination (#105)

vendor/golang.org/x/tools/internal/span/token111.go

@@ -0,0 +1,39 @@
+// 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
+		}
+	}
+}