x/exp/maps: Equal (and EqualFunc) don't take nilness of maps into account

[ainar-g]

What version of Go are you using (go version)?

$ go version
go version go1.19.3 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""                                                                                                                            
GOARCH="amd64"                                                                                                                            
GOBIN=""                                                                                                                                  
GOCACHE="/home/ainar/.cache/go-build"                                                                                                     
GOENV="/home/ainar/.config/go/env"                                                                                                        
GOEXE=""                                                                                                                                  
GOEXPERIMENT=""                                                                                                                           
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/ainar/go/pkg/mod"
GONOPROXY="REMOVED"
GONOSUMDB="REMOVED"
GOOS="linux"
GOPATH="/home/ainar/go"
GOPRIVATE="REMOVED"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/ainar/go/go1.19"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/ainar/go/go1.19/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.3"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/home/ainar/adg/AdGuardDNS/go.mod"
GOWORK="/home/ainar/adg/AdGuardDNS/go.work"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build594353111=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://go.dev/play/p/8A3M1ch-THs

What did you expect to see?

false

This is the result with reflect.DeepEqual: https://go.dev/play/p/46xr73EeC8p.

What did you see instead?

true

[EugeneOne1]

It seems the slices.Equal function (from x/exp/slices) behaves the same way. Here is the symmetrical example: https://go.dev/play/p/tzEpU_UIA_S.

I can file a separate issue about this one, if that is more convenient.

[seankhliao]

Note the documentation documents equality as same length.

[mknyszek]

CC @ianlancetaylor

[ianlancetaylor]

This is behaving as documented and intended. Thanks.