Update libkv dependency

vendor/golang.org/x/text/transform/transform.go

@@ -24,6 +24,10 @@ var (
 	// complete the transformation.
 	ErrShortSrc = errors.New("transform: short source buffer")
 
+	// ErrEndOfSpan means that the input and output (the transformed input)
+	// are not identical.
+	ErrEndOfSpan = errors.New("transform: input and output are not identical")
+
 	// errInconsistentByteCount means that Transform returned success (nil
 	// error) but also returned nSrc inconsistent with the src argument.
 	errInconsistentByteCount = errors.New("transform: inconsistent byte count returned")
@@ -60,6 +64,41 @@ type Transformer interface {
 	Reset()
 }
 
+// SpanningTransformer extends the Transformer interface with a Span method
+// that determines how much of the input already conforms to the Transformer.
+type SpanningTransformer interface {
+	Transformer
+
+	// Span returns a position in src such that transforming src[:n] results in
+	// identical output src[:n] for these bytes. It does not necessarily return
+	// the largest such n. The atEOF argument tells whether src represents the
+	// last bytes of the input.
+	//
+	// Callers should always account for the n bytes consumed before
+	// considering the error err.
+	//
+	// A nil error means that all input bytes are known to be identical to the
+	// output produced by the Transformer. A nil error can be be returned
+	// regardless of whether atEOF is true. If err is nil, then then n must
+	// equal len(src); the converse is not necessarily true.
+	//
+	// ErrEndOfSpan means that the Transformer output may differ from the
+	// input after n bytes. Note that n may be len(src), meaning that the output
+	// would contain additional bytes after otherwise identical output.
+	// ErrShortSrc means that src had insufficient data to determine whether the
+	// remaining bytes would change. Other than the error conditions listed
+	// here, implementations are free to report other errors that arise.
+	//
+	// Calling Span can modify the Transformer state as a side effect. In
+	// effect, it does the transformation just as calling Transform would, only
+	// without copying to a destination buffer and only up to a point it can
+	// determine the input and output bytes are the same. This is obviously more
+	// limited than calling Transform, but can be more efficient in terms of
+	// copying and allocating buffers. Calls to Span and Transform may be
+	// interleaved.
+	Span(src []byte, atEOF bool) (n int, err error)
+}
+
 // NopResetter can be embedded by implementations of Transformer to add a nop
 // Reset method.
 type NopResetter struct{}
@@ -278,6 +317,10 @@ func (nop) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
 	return n, n, err
 }
 
+func (nop) Span(src []byte, atEOF bool) (n int, err error) {
+	return len(src), nil
+}
+
 type discard struct{ NopResetter }
 
 func (discard) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
@@ -289,8 +332,8 @@ var (
 	// by consuming all bytes and writing nothing.
 	Discard Transformer = discard{}
 
-	// Nop is a Transformer that copies src to dst.
-	Nop Transformer = nop{}
+	// Nop is a SpanningTransformer that copies src to dst.
+	Nop SpanningTransformer = nop{}
 )
 
 // chain is a sequence of links. A chain with N Transformers has N+1 links and
@@ -358,6 +401,8 @@ func (c *chain) Reset() {
 	}
 }
 
+// TODO: make chain use Span (is going to be fun to implement!)
+
 // Transform applies the transformers of c in sequence.
 func (c *chain) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
 	// Set up src and dst in the chain.
@@ -448,8 +493,7 @@ func (c *chain) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err erro
 	return dstL.n, srcL.p, err
 }
 
-// RemoveFunc returns a Transformer that removes from the input all runes r for
-// which f(r) is true. Illegal bytes in the input are replaced by RuneError.
+// Deprecated: use runes.Remove instead.
 func RemoveFunc(f func(r rune) bool) Transformer {
 	return removeF(f)
 }