everything: fail to check err == nil when assigning explicit type to `error`

[liran-funaro]

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

This has been validated on other machines and Go version, as well as on https://go.dev/play.

$ go version
go version go1.19.3 darwin/arm64

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="arm64"
GOBIN=""
GOCACHE="/Users/liranfunaro/Library/Caches/go-build"
GOENV="/Users/liranfunaro/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/liranfunaro/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/liranfunaro/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16.9"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/liranfunaro/workspace/go-testing/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 -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/by/rgkh7tcn3yn0wdgxl63bynfc0000gn/T/go-build1699839087=/tmp/go-build -gno-record-gcc-switches -fno-common"
~/w/go-testing $ go1.19.3 env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/liranfunaro/Library/Caches/go-build"
GOENV="/Users/liranfunaro/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/liranfunaro/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/liranfunaro/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/liranfunaro/sdk/go1.19.3"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/liranfunaro/sdk/go1.19.3/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19.3"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/liranfunaro/workspace/go-testing/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/by/rgkh7tcn3yn0wdgxl63bynfc0000gn/T/go-build3375246314=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Here is a minimalist example that reproduces this error (play):

package main

import "fmt"

type MyError struct {
	Text string
}

func (e *MyError) Error() string {
	return fmt.Sprintf("msg: %s", e.Text)
}

func foo() *MyError {
	return nil
}

func main() {
	var typedErr *MyError
	typedErr = foo()
	fmt.Printf("       typedErr: %v\n", typedErr)
	fmt.Printf("typedErr == nil: %v\n\n", typedErr == nil)

	var err error
	err = foo()
	fmt.Printf("            err: %v\n", err)
	fmt.Printf("     err == nil: %v\n\n", err == nil)
}

What did you expect to see?

I expect that err == nil in both cases as foo() always returns nil.

       typedErr: <nil>
typedErr == nil: true

            err: <nil>
     err == nil: true

What did you see instead?

But when I assigned foo() to a generic error variable, then the check err == nil return false even though it is clearly visible that err is nil as printed right above it.

       typedErr: <nil>
typedErr == nil: true

            err: <nil>
     err == nil: false

[seankhliao]

https://go.dev/doc/faq#nil_error

Unlike many projects, the Go project does not use GitHub Issues for general discussion or asking questions. GitHub Issues are used for tracking bugs and proposals only.

For questions please refer to https://github.com/golang/go/wiki/Questions