Pull request:* all: remove github.com/joomcode/errorx dependency

Merge in DNS/adguard-home from 2240-removing-errorx-dependency to master

Squashed commit of the following:

commit 5bbe0567356f06e3b9ee5b3dc38d357b472cacb1
Merge: a6040850d 02d16a0b4
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Nov 5 14:32:22 2020 +0300

    Merge branch 'master' into 2240-removing-errorx-dependency

commit a6040850da3cefb131208097477b0956e80063fb
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Nov 5 14:23:36 2020 +0300

    * dhcpd: convert some abbreviations to lowercase.

commit d05bd51b994906b0ff52c5a8e779bd1f512f4bb7
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Nov 5 12:47:20 2020 +0300

    * agherr: last final fixes

commit 164bca55035ff44e50b0abb33e129a0d24ffe87c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Nov 3 19:11:10 2020 +0300

    * all: final fixes again

commit a0ac26f409c0b28a176cf2861d52c2f471b59484
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Nov 3 18:51:39 2020 +0300

    * all: final fixes

commit 6147b02d402b513323b07e85856b348884f3a088
Merge: 9fd3af1a3 62cc334f4
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 18:26:03 2020 +0300

    Merge branch 'master' into 2240-removing-errorx-dependency

commit 9fd3af1a39a3189b5c41315a8ad1568ae5cb4fc9
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 18:23:08 2020 +0300

    * all: remove useless helper

commit 7cd9aeae639762b28b25f354d69c5cf74f670211
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 17:19:26 2020 +0300

    * agherr: improved code tidiness

commit a74a49236e9aaace070646dac710de9201105262
Merge: dc9dedbf2 df34ee5c0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 16:54:29 2020 +0300

    Merge branch 'master' into 2240-removing-errorx-dependency

commit dc9dedbf205756e3adaa3bc776d349bf3d8c69a5
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 16:40:08 2020 +0300

    * agherr: improve and cover by tests

commit fd6bfe9e282156cc60e006cb7cd46cce4d3a07a8
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 14:06:27 2020 +0300

    * all: improve code quality

commit ea00c2f8c5060e9611f9a80cfd0e4a039526d0c4
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 13:03:57 2020 +0300

    * all: fix linter style warnings

commit 8e75e1a681a7218c2b4c69adfa2b7e1e2966f9ac
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 3 12:29:26 2020 +0300

    * all: remove github.com/joomcode/errorx dependency

    Closes #2240.

internal/agherr/agherr.go

@@ -0,0 +1,59 @@
+// Package agherr contains the extended error type, and the function for
+// wrapping several errors.
+package agherr
+
+import (
+	"fmt"
+	"strings"
+)
+
+// manyError is an error containing several wrapped errors.  It is created to be
+// a simpler version of the API provided by github.com/joomcode/errorx.
+type manyError struct {
+	message    string
+	underlying []error
+}
+
+// Many wraps several errors and returns a single error.
+func Many(message string, underlying ...error) error {
+	err := &manyError{
+		message:    message,
+		underlying: underlying,
+	}
+
+	return err
+}
+
+// Error implements the error interface for *manyError.
+func (e *manyError) Error() string {
+	switch len(e.underlying) {
+	case 0:
+		return e.message
+	case 1:
+		return fmt.Sprintf("%s: %s", e.message, e.underlying[0])
+	default:
+		b := &strings.Builder{}
+
+		// Ignore errors, since strings.(*Buffer).Write never returns
+		// errors.
+		_, _ = fmt.Fprintf(b, "%s: %s (hidden: %s", e.message, e.underlying[0], e.underlying[1])
+		for _, u := range e.underlying[2:] {
+			// See comment above.
+			_, _ = fmt.Fprintf(b, ", %s", u)
+		}
+
+		// See comment above.
+		_, _ = b.WriteString(")")
+
+		return b.String()
+	}
+}
+
+// Unwrap implements the hidden errors.wrapper interface for *manyError.
+func (e *manyError) Unwrap() error {
+	if len(e.underlying) == 0 {
+		return nil
+	}
+
+	return e.underlying[0]
+}

internal/agherr/agherr_test.go

@@ -0,0 +1,73 @@
+package agherr
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestError_Error(t *testing.T) {
+	testCases := []struct {
+		name string
+		want string
+		err  error
+	}{{
+		name: "simple",
+		want: "a",
+		err:  Many("a"),
+	}, {
+		name: "wrapping",
+		want: "a: b",
+		err:  Many("a", errors.New("b")),
+	}, {
+		name: "wrapping several",
+		want: "a: b (hidden: c, d)",
+		err:  Many("a", errors.New("b"), errors.New("c"), errors.New("d")),
+	}, {
+		name: "wrapping wrapper",
+		want: "a: b: c (hidden: d)",
+		err:  Many("a", Many("b", errors.New("c"), errors.New("d"))),
+	}}
+	for _, tc := range testCases {
+		assert.Equal(t, tc.want, tc.err.Error(), tc.name)
+	}
+}
+
+func TestError_Unwrap(t *testing.T) {
+	const (
+		errSimple = iota
+		errWrapped
+		errNil
+	)
+	errs := []error{
+		errSimple:  errors.New("a"),
+		errWrapped: fmt.Errorf("%w", errors.New("nested")),
+		errNil:     nil,
+	}
+	testCases := []struct {
+		name    string
+		want    error
+		wrapped error
+	}{{
+		name:    "simple",
+		want:    errs[errSimple],
+		wrapped: Many("a", errs[errSimple]),
+	}, {
+		name:    "nested",
+		want:    errs[errWrapped],
+		wrapped: Many("b", errs[errWrapped]),
+	}, {
+		name:    "nil passed",
+		want:    errs[errNil],
+		wrapped: Many("c", errs[errNil]),
+	}, {
+		name:    "nil not passed",
+		want:    nil,
+		wrapped: Many("d"),
+	}}
+	for _, tc := range testCases {
+		assert.Equal(t, tc.want, errors.Unwrap(tc.wrapped), tc.name)
+	}
+}