errors, fmt: revert rejected changes for Go 1.13

Reverts the following changes:

  https://go.googlesource.com/go/+/1f90d081391d4f5911960fd28d81d7ea5e554a8f
  https://go.googlesource.com/go/+/8bf18b56a47a98b9dd2fa03beb358312237a8c76
  https://go.googlesource.com/go/+/5402854c3557f87fa2741a52ffc15dfb1ef333cc
  https://go.googlesource.com/go/+/37f84817247d3b8e687a701ccb0d6bc7ffe3cb78
  https://go.googlesource.com/go/+/6be6f114e0d483a233101a67c9644cd72bd3ae7a

Partially reverts the followinng change, removing the errors.Opaque
function and the errors.Wrapper type definition:

  https://go.googlesource.com/go/+/62f5e8156ef56fa61e6af56f4ccc633bde1a9120

Updates documentation referencing the Wrapper type.

Change-Id: Ia622883e39cafb06809853e3fd90b21441124534
Reviewed-on: https://go-review.googlesource.com/c/go/+/176997
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

1 files changed, 0 insertions, 46 deletions

diff --git a/src/fmt/format_example_test.go b/src/fmt/format_example_test.go
deleted file mode 100644
index 386f10ef23..0000000000
--- a/src/fmt/format_example_test.go
+++ /dev/null
@@ -1,46 +0,0 @@
-// Copyright 2018 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.
-
-package fmt_test
-
-import (
-	"errors"
-	"fmt"
-	"path/filepath"
-	"regexp"
-)
-
-func baz() error { return errors.New("baz flopped") }
-func bar() error { return fmt.Errorf("bar(nameserver 139): %v", baz()) }
-func foo() error { return fmt.Errorf("foo: %s", bar()) }
-
-func Example_formatting() {
-	err := foo()
-	fmt.Println("Error:")
-	fmt.Printf("%v\n", err)
-	fmt.Println()
-	fmt.Println("Detailed error:")
-	fmt.Println(stripPath(fmt.Sprintf("%+v\n", err)))
-	// Output:
-	// Error:
-	// foo: bar(nameserver 139): baz flopped
-	//
-	// Detailed error:
-	// foo:
-	//     fmt_test.foo
-	//         fmt/format_example_test.go:16
-	//   - bar(nameserver 139):
-	//     fmt_test.bar
-	//         fmt/format_example_test.go:15
-	//   - baz flopped:
-	//     fmt_test.baz
-	//         fmt/format_example_test.go:14
-}
-
-func stripPath(s string) string {
-	rePath := regexp.MustCompile(`( [^ ]*)fmt`)
-	s = rePath.ReplaceAllString(s, " fmt")
-	s = filepath.ToSlash(s)
-	return s
-}