text/tabwriter: remove internal use of bytes.Buffer (cleanup)

Noticed that we can simply use a []byte slice while investigating
a separate issue. Did the obvious simplification.

Change-Id: I921ebbb42135b5f1a10109236ceb9ae6e94ae7e2
Reviewed-on: https://go-review.googlesource.com/104757
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/text/tabwriter/tabwriter.go

@@ -12,7 +12,6 @@
 package tabwriter
 
 import (
-	"bytes"
 	"io"
 	"unicode/utf8"
 )
@@ -99,19 +98,19 @@ type Writer struct {
 	flags    uint
 
 	// current state
-	buf     bytes.Buffer // collected text excluding tabs or line breaks
-	pos     int          // buffer position up to which cell.width of incomplete cell has been computed
-	cell    cell         // current incomplete cell; cell.width is up to buf[pos] excluding ignored sections
-	endChar byte         // terminating char of escaped sequence (Escape for escapes, '>', ';' for HTML tags/entities, or 0)
-	lines   [][]cell     // list of lines; each line is a list of cells
-	widths  []int        // list of column widths in runes - re-used during formatting
+	buf     []byte   // collected text excluding tabs or line breaks
+	pos     int      // buffer position up to which cell.width of incomplete cell has been computed
+	cell    cell     // current incomplete cell; cell.width is up to buf[pos] excluding ignored sections
+	endChar byte     // terminating char of escaped sequence (Escape for escapes, '>', ';' for HTML tags/entities, or 0)
+	lines   [][]cell // list of lines; each line is a list of cells
+	widths  []int    // list of column widths in runes - re-used during formatting
 }
 
 func (b *Writer) addLine() { b.lines = append(b.lines, []cell{}) }
 
 // Reset the current state.
 func (b *Writer) reset() {
-	b.buf.Reset()
+	b.buf = b.buf[:0]
 	b.pos = 0
 	b.cell = cell{}
 	b.endChar = 0
@@ -212,7 +211,7 @@ func (b *Writer) dump() {
 	for i, line := range b.lines {
 		print("(", i, ") ")
 		for _, c := range line {
-			print("[", string(b.buf.Bytes()[pos:pos+c.size]), "]")
+			print("[", string(b.buf[pos:pos+c.size]), "]")
 			pos += c.size
 		}
 		print("\n")
@@ -294,7 +293,7 @@ func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
 				// non-empty cell
 				useTabs = false
 				if b.flags&AlignRight == 0 { // align left
-					b.write0(b.buf.Bytes()[pos : pos+c.size])
+					b.write0(b.buf[pos : pos+c.size])
 					pos += c.size
 					if j < len(b.widths) {
 						b.writePadding(c.width, b.widths[j], false)
@@ -303,7 +302,7 @@ func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
 					if j < len(b.widths) {
 						b.writePadding(c.width, b.widths[j], false)
 					}
-					b.write0(b.buf.Bytes()[pos : pos+c.size])
+					b.write0(b.buf[pos : pos+c.size])
 					pos += c.size
 				}
 			}
@@ -312,7 +311,7 @@ func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
 		if i+1 == len(b.lines) {
 			// last buffered line - we don't have a newline, so just write
 			// any outstanding buffered data
-			b.write0(b.buf.Bytes()[pos : pos+b.cell.size])
+			b.write0(b.buf[pos : pos+b.cell.size])
 			pos += b.cell.size
 		} else {
 			// not the last line - write newline
@@ -387,14 +386,14 @@ func (b *Writer) format(pos0 int, line0, line1 int) (pos int) {
 
 // Append text to current cell.
 func (b *Writer) append(text []byte) {
-	b.buf.Write(text)
+	b.buf = append(b.buf, text...)
 	b.cell.size += len(text)
 }
 
 // Update the cell width.
 func (b *Writer) updateWidth() {
-	b.cell.width += utf8.RuneCount(b.buf.Bytes()[b.pos:b.buf.Len()])
-	b.pos = b.buf.Len()
+	b.cell.width += utf8.RuneCount(b.buf[b.pos:])
+	b.pos = len(b.buf)
 }
 
 // To escape a text segment, bracket it with Escape characters.
@@ -434,7 +433,7 @@ func (b *Writer) endEscape() {
 	case ';':
 		b.cell.width++ // entity, count as one rune
 	}
-	b.pos = b.buf.Len()
+	b.pos = len(b.buf)
 	b.endChar = 0
 }