reflect: potential change required in DeepEqual

[obourdon]

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

$ go version
go version go1.13.7 darwin/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="/Users/XXX/Library/Caches/go-build"
GOENV="/Users/XXX/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/XXX/.gvm/pkgsets/go1.13.7/global"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/XXX/.gvm/gos/go1.13.7"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/XXX/.gvm/gos/go1.13.7/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/XXX/Documents/WORK/SquareScale/HASHICORP/terraform-provider-aws/go.mod"
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 -fmessage-length=0 -fdebug-prefix-map=/var/folders/k0/35x3347j4s18t_h4z932f3nr0000gn/T/go-build598493337=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

See issue # 11059 in Terraform AWS Provider

and more specifically this part

DeepEqual fails because of the following item which is however perfectly identical in both cases:

 F: (schema.SchemaSetFunc) 0x4ec7530,

What did you expect to see?

If pointer addresses are identical true should be returned so something like:

	case Func:
		if v1.IsNil() && v2.IsNil() {
			return true
		}
		// Can't do better than this:
		return v1 == v2

might be better (IMHO)

What did you see instead?

DeepEqual returns false

[obourdon]

After reading a bit more about function comparison, which does not seem very obvious, may be we could just parameterize the DeepEqual call so that this check can be disabled ? Just wondering ...

[bcmills]

Per https://golang.org/ref/spec#Comparison_operators:

Slice, map, and function values are not comparable. However, as a special case, a slice, map, or function value may be compared to the predeclared identifier nil.

And per the reflect.DeepEqual documentation:

Func values are deeply equal if both are nil; otherwise they are not deeply equal.

Any change to that behavior would violate the Go 1 compatibility policy.

[ianlancetaylor]

Sorry, we aren't going to make this change in reflect.DeepEqual. There are many possible ways of doing equality comparisons. DeepEqual is one of them. Many people find it useful, but there are many possible variants. We don't want to try to provide all those variants. You can use DeepEqual as a template for your own equality function.

[obourdon]

@ianlancetaylor @bcmills many thanks for this feedback, I fully understand.Many thanks again