2 files changed, 118 insertions, 43 deletions

diff --git a/vendor/golang.org/x/xerrors/doc.go b/vendor/golang.org/x/xerrors/doc.go
index 1ad48f50b..eef99d9d5 100644
--- a/vendor/golang.org/x/xerrors/doc.go
+++ b/vendor/golang.org/x/xerrors/doc.go
@@ -4,22 +4,19 @@
 
 // Package xerrors implements functions to manipulate errors.
 //
-// This package supports transitioning to the Go 2 proposal for error values:
+// This package is based on the Go 2 proposal for error values:
 //   https://golang.org/design/29934-error-values
 //
-// Most of the functions and types in this package will be incorporated into the
-// standard library's errors package in Go 1.13; the behavior of this package's
-// Errorf function will be incorporated into the standard library's fmt.Errorf.
-// Use this package to get equivalent behavior in all supported Go versions. For
-// example, create errors using
+// These functions were incorporated into the standard library's errors package
+// in Go 1.13:
+// - Is
+// - As
+// - Unwrap
 //
-//    xerrors.New("write failed")
+// Also, Errorf's %w verb was incorporated into fmt.Errorf.
 //
-// or
+// Use this package to get equivalent behavior in all supported Go versions.
 //
-//    xerrors.Errorf("while reading: %v", err)
-//
-// If you want your error type to participate in the new formatting
-// implementation for %v and %+v, provide it with a Format method that calls
-// xerrors.FormatError, as shown in the example for FormatError.
+// No other features of this package were included in Go 1.13, and at present
+// there are no plans to include any of them.
 package xerrors // import "golang.org/x/xerrors"
diff --git a/vendor/golang.org/x/xerrors/fmt.go b/vendor/golang.org/x/xerrors/fmt.go
index 74c1c93ec..829862ddf 100644
--- a/vendor/golang.org/x/xerrors/fmt.go
+++ b/vendor/golang.org/x/xerrors/fmt.go
@@ -7,10 +7,14 @@ package xerrors
 import (
 	"fmt"
 	"strings"
+	"unicode"
+	"unicode/utf8"
 
 	"golang.org/x/xerrors/internal"
 )
 
+const percentBangString = "%!"
+
 // Errorf formats according to a format specifier and returns the string as a
 // value that satisfies error.
 //
@@ -18,29 +22,71 @@ import (
 // formatted with additional detail enabled. If the last argument is an error
 // the returned error's Format method will return it if the format string ends
 // with ": %s", ": %v", or ": %w". If the last argument is an error and the
-// format string ends with ": %w", the returned error implements Wrapper
-// with an Unwrap method returning it.
+// format string ends with ": %w", the returned error implements an Unwrap
+// method returning it.
+//
+// If the format specifier includes a %w verb with an error operand in a
+// position other than at the end, the returned error will still implement an
+// Unwrap method returning the operand, but the error's Format method will not
+// return the wrapped error.
+//
+// It is invalid to include more than one %w verb or to supply it with an
+// operand that does not implement the error interface. The %w verb is otherwise
+// a synonym for %v.
 func Errorf(format string, a ...interface{}) error {
-	err, wrap := lastError(format, a)
 	format = formatPlusW(format)
-	if err == nil {
-		return &noWrapError{fmt.Sprintf(format, a...), nil, Caller(1)}
+	// Support a ": %[wsv]" suffix, which works well with xerrors.Formatter.
+	wrap := strings.HasSuffix(format, ": %w")
+	idx, format2, ok := parsePercentW(format)
+	percentWElsewhere := !wrap && idx >= 0
+	if !percentWElsewhere && (wrap || strings.HasSuffix(format, ": %s") || strings.HasSuffix(format, ": %v")) {
+		err := errorAt(a, len(a)-1)
+		if err == nil {
+			return &noWrapError{fmt.Sprintf(format, a...), nil, Caller(1)}
+		}
+		// TODO: this is not entirely correct. The error value could be
+		// printed elsewhere in format if it mixes numbered with unnumbered
+		// substitutions. With relatively small changes to doPrintf we can
+		// have it optionally ignore extra arguments and pass the argument
+		// list in its entirety.
+		msg := fmt.Sprintf(format[:len(format)-len(": %s")], a[:len(a)-1]...)
+		frame := Frame{}
+		if internal.EnableTrace {
+			frame = Caller(1)
+		}
+		if wrap {
+			return &wrapError{msg, err, frame}
+		}
+		return &noWrapError{msg, err, frame}
+	}
+	// Support %w anywhere.
+	// TODO: don't repeat the wrapped error's message when %w occurs in the middle.
+	msg := fmt.Sprintf(format2, a...)
+	if idx < 0 {
+		return &noWrapError{msg, nil, Caller(1)}
+	}
+	err := errorAt(a, idx)
+	if !ok || err == nil {
+		// Too many %ws or argument of %w is not an error. Approximate the Go
+		// 1.13 fmt.Errorf message.
+		return &noWrapError{fmt.Sprintf("%sw(%s)", percentBangString, msg), nil, Caller(1)}
 	}
-
-	// TODO: this is not entirely correct. The error value could be
-	// printed elsewhere in format if it mixes numbered with unnumbered
-	// substitutions. With relatively small changes to doPrintf we can
-	// have it optionally ignore extra arguments and pass the argument
-	// list in its entirety.
-	msg := fmt.Sprintf(format[:len(format)-len(": %s")], a[:len(a)-1]...)
 	frame := Frame{}
 	if internal.EnableTrace {
 		frame = Caller(1)
 	}
-	if wrap {
-		return &wrapError{msg, err, frame}
+	return &wrapError{msg, err, frame}
+}
+
+func errorAt(args []interface{}, i int) error {
+	if i < 0 || i >= len(args) {
+		return nil
 	}
-	return &noWrapError{msg, err, frame}
+	err, ok := args[i].(error)
+	if !ok {
+		return nil
+	}
+	return err
 }
 
 // formatPlusW is used to avoid the vet check that will barf at %w.
@@ -48,24 +94,56 @@ func formatPlusW(s string) string {
 	return s
 }
 
-func lastError(format string, a []interface{}) (err error, wrap bool) {
-	wrap = strings.HasSuffix(format, ": %w")
-	if !wrap &&
-		!strings.HasSuffix(format, ": %s") &&
-		!strings.HasSuffix(format, ": %v") {
-		return nil, false
-	}
-
-	if len(a) == 0 {
-		return nil, false
+// Return the index of the only %w in format, or -1 if none.
+// Also return a rewritten format string with %w replaced by %v, and
+// false if there is more than one %w.
+// TODO: handle "%[N]w".
+func parsePercentW(format string) (idx int, newFormat string, ok bool) {
+	// Loosely copied from golang.org/x/tools/go/analysis/passes/printf/printf.go.
+	idx = -1
+	ok = true
+	n := 0
+	sz := 0
+	var isW bool
+	for i := 0; i < len(format); i += sz {
+		if format[i] != '%' {
+			sz = 1
+			continue
+		}
+		// "%%" is not a format directive.
+		if i+1 < len(format) && format[i+1] == '%' {
+			sz = 2
+			continue
+		}
+		sz, isW = parsePrintfVerb(format[i:])
+		if isW {
+			if idx >= 0 {
+				ok = false
+			} else {
+				idx = n
+			}
+			// "Replace" the last character, the 'w', with a 'v'.
+			p := i + sz - 1
+			format = format[:p] + "v" + format[p+1:]
+		}
+		n++
 	}
+	return idx, format, ok
+}
 
-	err, ok := a[len(a)-1].(error)
-	if !ok {
-		return nil, false
+// Parse the printf verb starting with a % at s[0].
+// Return how many bytes it occupies and whether the verb is 'w'.
+func parsePrintfVerb(s string) (int, bool) {
+	// Assume only that the directive is a sequence of non-letters followed by a single letter.
+	sz := 0
+	var r rune
+	for i := 1; i < len(s); i += sz {
+		r, sz = utf8.DecodeRuneInString(s[i:])
+		if unicode.IsLetter(r) {
+			return i + sz, r == 'w'
+		}
 	}
-
-	return err, wrap
+	return len(s), false
 }
 
 type noWrapError struct {