import/path: custom error does not equal nil when returned from a child func

[radulucut]

Go version

go version go1.23.0 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOVCS=''
GOVERSION='go1.23.0'
GODEBUG=''
GOTELEMETRY='local'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'

What did you do?

package main

import "fmt"

type CustomError struct {
	Message string
}

func (e *CustomError) Error() string {
	return e.Message
}

func main() {
	fmt.Println(parent() == nil)
}

func parent() error {
	return child()
}

func child() *CustomError {
	return nil
}

https://go.dev/play/p/AYl4dQpc2pm

What did you see happen?

I expect the result of the parent() function to equal nil.

What did you expect to see?

I expect the result of the parent() function to equal nil.
If the child() function' return type is set to error, it will work fine.

[gabyhelp]

Related Issues and Documentation

• Function nesting calls a function that returns a pointer that implements the error, the returned error is always not equal to nil #43767 (closed)
• Nil custom error returned from function not treated as nil #35217 (closed)
• builtin/error: return value mismatch between "error interface" and custom error struct #54229 (closed)
• Nil check for custom errors in some situations are incorrect #31873 (closed)
• builtin/error: late assignment of custom error type cause nil checking of the error variable not working #53768 (closed)
• everything: fail to check err == nil when assigning explicit type to `error` #56930 (closed)
• error: it's really easy make mistake that return custom error assign to defined interface error #20389 (closed)
• `err != nil` when `err == nil` with custom `error` type #35292 (closed)
• errors: Is(nil) behaves unexpectedly #40442 (closed)
• Nil-ness of a pointer is lost when converted to an interface #42306 (closed)

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