golang.org/x/text/width: patch sample

transform.patch

diff --git width/transform.go width/transform.go
index 8dd731c..ec8be34 100644
--- width/transform.go
+++ width/transform.go
@@ -22,7 +22,7 @@ func (foldTransform) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err
            if d := len(dst) - nDst; d < end-start {
                end = nSrc + d
            }
-           for nSrc++; nSrc < end && src[nSrc] < utf8.RuneSelf; nSrc++ {
+           for ; nSrc < end && src[nSrc] < utf8.RuneSelf; nSrc++ {
            }
            nDst += copy(dst[nDst:], src[start:nSrc])
            if nDst == len(dst) && nSrc < len(src) && src[nSrc] < utf8.RuneSelf {
@@ -72,7 +72,7 @@ func (narrowTransform) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, e
            if d := len(dst) - nDst; d < end-start {
                end = nSrc + d
            }
-           for nSrc++; nSrc < end && src[nSrc] < utf8.RuneSelf; nSrc++ {
+           for ; nSrc < end && src[nSrc] < utf8.RuneSelf; nSrc++ {
            }
            nDst += copy(dst[nDst:], src[start:nSrc])
            if nDst == len(dst) && nSrc < len(src) && src[nSrc] < utf8.RuneSelf {

transform_test.patch

diff --git width/transform_test.go width/transform_test.go
index 535f24d..e7c43ea 100644
--- width/transform_test.go
+++ width/transform_test.go
@@ -6,6 +6,7 @@ package width

 import (
    "bytes"
+   "strings"
    "testing"

    "golang.org/x/text/internal/testtext"
@@ -132,6 +133,14 @@ func TestFold(t *testing.T) {
        atEOF: true,
        err:   transform.ErrShortDst,
    }, {
+       desc:  "empty dst fast path",
+       src:   "fast",
+       dst:   "",
+       nDst:  0,
+       nSrc:  0,
+       atEOF: true,
+       err:   transform.ErrShortDst,
+   }, {
        desc:  "fast path alternation",
        src:   "fast路徑fast路徑",
        dst:   "fast路徑fast路徑",
@@ -377,6 +386,14 @@ func TestNarrow(t *testing.T) {
        atEOF: true,
        err:   transform.ErrShortDst,
    }, {
+       desc:  "empty dst fast path",
+       src:   "fast",
+       dst:   "",
+       nDst:  0,
+       nSrc:  0,
+       atEOF: true,
+       err:   transform.ErrShortDst,
+   }, {
        desc:  "fast path alternation",
        src:   "fast路徑fast路徑",
        dst:   "fast路徑fast路徑",
@@ -465,3 +482,39 @@ func BenchmarkNarrowNonCanonical(b *testing.B) {
 func BenchmarkNarrowOther(b *testing.B) {
    bench(b, Narrow, testtext.TwoByteUTF8+testtext.ThreeByteUTF8)
 }
+
+const initialBufSize = 128 // initialBufSize from golang.org/x/text/transform/transform.go
+
+func TestFoldLongString(t *testing.T) {
+   for i, s := range []string{
+       "\uff21" + strings.Repeat("A", initialBufSize-1),
+       "\uff21" + strings.Repeat("A", initialBufSize+0),
+       "\uff21" + strings.Repeat("A", initialBufSize+1),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+1),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+0),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+1),
+   } {
+       got := Fold.String(s)
+       want := strings.Repeat("A", len(s)-len(w)+1)
+       if got != want {
+           t.Errorf("%d:Fold String test: got %s (%d); want %s (%d)", i, got, len(got), want, len(want))
+       }
+   }
+}
+
+func TestNarrowLongString(t *testing.T) {
+   for i, s := range []string{
+       "\uff21" + strings.Repeat("A", initialBufSize-1),
+       "\uff21" + strings.Repeat("A", initialBufSize+0),
+       "\uff21" + strings.Repeat("A", initialBufSize+1),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+1),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+0),
+       "\uff21" + strings.Repeat("A", 2*initialBufSize+1),
+   } {
+       got := Narrow.String(s)
+       want := strings.Repeat("A", len(s)-len("\uff21")+1)
+       if got != want {
+           t.Errorf("%d:Fold String test: got %s (%d); want %s (%d)", i, got, len(got), want, len(want))
+       }
+   }
+}