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Add cmpopts.EquateComparable #340

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Aug 31, 2023
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4 changes: 2 additions & 2 deletions .github/workflows/test.yml
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ jobs:
test:
strategy:
matrix:
go-version: [1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x, 1.19.x, 1.20.x]
go-version: [1.18.x, 1.19.x, 1.20.x, 1.21.x]
os: [ubuntu-latest, macos-latest]
runs-on: ${{ matrix.os }}
steps:
Expand All @@ -19,5 +19,5 @@ jobs:
- name: Test
run: go test -v -race ./...
- name: Format
if: matrix.go-version == '1.20.x'
if: matrix.go-version == '1.21.x'
run: diff -u <(echo -n) <(gofmt -d .)
29 changes: 29 additions & 0 deletions cmp/cmpopts/equate.go
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ package cmpopts

import (
"errors"
"fmt"
"math"
"reflect"
"time"
Expand Down Expand Up @@ -154,3 +155,31 @@ func compareErrors(x, y interface{}) bool {
ye := y.(error)
return errors.Is(xe, ye) || errors.Is(ye, xe)
}

// EquateComparable returns a [cmp.Option] that determines equality
// of comparable types by directly comparing them using the == operator in Go.
// The types to compare are specified by passing a value of that type.
// This option should only be used on types that are documented as being
// safe for direct == comparison. For example, [net/netip.Addr] is documented
// as being semantically safe to use with ==, while [time.Time] is documented
// to discourage the use of == on time values.
func EquateComparable(typs ...interface{}) cmp.Option {
types := make(typesFilter)
for _, typ := range typs {
switch t := reflect.TypeOf(typ); {
case !t.Comparable():
panic(fmt.Sprintf("%T is not a comparable Go type", typ))
case types[t]:
panic(fmt.Sprintf("%T is already specified", typ))
default:
types[t] = true
}
}
return cmp.FilterPath(types.filter, cmp.Comparer(equateAny))
}

type typesFilter map[reflect.Type]bool

func (tf typesFilter) filter(p cmp.Path) bool { return tf[p.Last().Type()] }

func equateAny(x, y interface{}) bool { return x == y }
31 changes: 31 additions & 0 deletions cmp/cmpopts/util_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ import (
"fmt"
"io"
"math"
"net/netip"
"reflect"
"strings"
"sync"
Expand Down Expand Up @@ -676,6 +677,36 @@ func TestOptions(t *testing.T) {
opts: []cmp.Option{EquateErrors()},
wantEqual: false,
reason: "AnyError is not equal to nil value",
}, {
label: "EquateComparable",
x: []struct{ P netip.Addr }{
{netip.AddrFrom4([4]byte{1, 2, 3, 4})},
{netip.AddrFrom4([4]byte{1, 2, 3, 5})},
{netip.AddrFrom4([4]byte{1, 2, 3, 6})},
},
y: []struct{ P netip.Addr }{
{netip.AddrFrom4([4]byte{1, 2, 3, 4})},
{netip.AddrFrom4([4]byte{1, 2, 3, 5})},
{netip.AddrFrom4([4]byte{1, 2, 3, 6})},
},
opts: []cmp.Option{EquateComparable(netip.Addr{})},
wantEqual: true,
reason: "equal because all IP addresses are the same",
}, {
label: "EquateComparable",
x: []struct{ P netip.Addr }{
{netip.AddrFrom4([4]byte{1, 2, 3, 4})},
{netip.AddrFrom4([4]byte{1, 2, 3, 5})},
{netip.AddrFrom4([4]byte{1, 2, 3, 6})},
},
y: []struct{ P netip.Addr }{
{netip.AddrFrom4([4]byte{1, 2, 3, 4})},
{netip.AddrFrom4([4]byte{1, 2, 3, 7})},
{netip.AddrFrom4([4]byte{1, 2, 3, 6})},
},
opts: []cmp.Option{EquateComparable(netip.Addr{})},
wantEqual: false,
reason: "not equal because second IP address is different",
}, {
label: "IgnoreFields",
x: Bar1{Foo3{&Foo2{&Foo1{Alpha: 5}}}},
Expand Down
2 changes: 2 additions & 0 deletions cmp/options.go
Original file line number Diff line number Diff line change
Expand Up @@ -234,6 +234,8 @@ func (validator) apply(s *state, vx, vy reflect.Value) {
name = fmt.Sprintf("%q.%v", t.PkgPath(), t.Name()) // e.g., "path/to/package".MyType
if _, ok := reflect.New(t).Interface().(error); ok {
help = "consider using cmpopts.EquateErrors to compare error values"
} else if t.Comparable() {
help = "consider using cmpopts.EquateComparable to compare comparable Go types"
}
} else {
// Unnamed type with unexported fields. Derive PkgPath from field.
Expand Down
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