remove xerrors (#292)

Versions older than Go 1.13 are no longer in use. Remove unnecessary
dependencies.

.github/workflows/test.yml

@@ -4,7 +4,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.11.x, 1.12.x, 1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x]
+        go-version: [1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x]
         os: [ubuntu-latest, macos-latest]
     runs-on: ${{ matrix.os }}
     steps:

cmp/cmpopts/util_test.go

@@ -17,7 +17,6 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"golang.org/x/xerrors"
 )
 
 type (
@@ -531,14 +530,14 @@ func TestOptions(t *testing.T) {
 		reason:    "user-defined EOF is not exactly equal",
 	}, {
 		label:     "EquateErrors",
-		x:         xerrors.Errorf("wrapped: %w", io.EOF),
+		x:         fmt.Errorf("wrapped: %w", io.EOF),
 		y:         io.EOF,
 		opts:      []cmp.Option{EquateErrors()},
 		wantEqual: true,
 		reason:    "wrapped io.EOF is equal according to errors.Is",
 	}, {
 		label:     "EquateErrors",
-		x:         xerrors.Errorf("wrapped: %w", io.EOF),
+		x:         fmt.Errorf("wrapped: %w", io.EOF),
 		y:         io.EOF,
 		wantEqual: false,
 		reason:    "wrapped io.EOF is not equal without EquateErrors option",
@@ -585,14 +584,14 @@ func TestOptions(t *testing.T) {
 		reason:    "user-defined EOF is not exactly equal",
 	}, {
 		label:     "EquateErrors",
-		x:         xerrors.Errorf("wrapped: %w", io.EOF),
+		x:         fmt.Errorf("wrapped: %w", io.EOF),
 		y:         io.EOF,
 		opts:      []cmp.Option{EquateErrors()},
 		wantEqual: true,
 		reason:    "wrapped io.EOF is equal according to errors.Is",
 	}, {
 		label:     "EquateErrors",
-		x:         xerrors.Errorf("wrapped: %w", io.EOF),
+		x:         fmt.Errorf("wrapped: %w", io.EOF),
 		y:         io.EOF,
 		wantEqual: false,
 		reason:    "wrapped io.EOF is not equal without EquateErrors option",
@@ -639,14 +638,14 @@ func TestOptions(t *testing.T) {
 		reason:    "user-defined EOF is not exactly equal",
 	}, {
 		label:     "EquateErrors",
-		x:         struct{ E error }{xerrors.Errorf("wrapped: %w", io.EOF)},
+		x:         struct{ E error }{fmt.Errorf("wrapped: %w", io.EOF)},
 		y:         struct{ E error }{io.EOF},
 		opts:      []cmp.Option{EquateErrors()},
 		wantEqual: true,
 		reason:    "wrapped io.EOF is equal according to errors.Is",
 	}, {
 		label:     "EquateErrors",
-		x:         struct{ E error }{xerrors.Errorf("wrapped: %w", io.EOF)},
+		x:         struct{ E error }{fmt.Errorf("wrapped: %w", io.EOF)},
 		y:         struct{ E error }{io.EOF},
 		wantEqual: false,
 		reason:    "wrapped io.EOF is not equal without EquateErrors option",

go.mod

@@ -1,5 +1,3 @@
 module github.com/google/go-cmp
 
 go 1.11
-
-require golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543