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

$ go version
go version go1.12.7 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

$ go env
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\howard\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\howard\go
set GOPROXY=
set GORACE=
set GOROOT=c:\go
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\howard\AppData\Local\Temp\go-build943471142=/tmp/go-build -gno-record-gcc-switches

What did you do?

Run this code snippet

package main

import (
	"context"
	"fmt"
	"net"
)

func main() {
	resolver := &net.Resolver{
		PreferGo:     true,
		StrictErrors: true,
		Dial: func(ctx context.Context, network, address string) (conn net.Conn, e error) {
			panic(nil)
		},
	}
	result, err := resolver.LookupHost(context.Background(), "google.com")
	fmt.Println(result, err)
}

What did you expect to see?

A panic, as correctly demonstrated by running the snippet under Linux:

panic: nil

goroutine 6 [running]:
main.main.func1(0x53caa0, 0xc00007a300, 0x51a125, 0x3, 0xc0000183f0, 0xe, 0x42aedc, 0xc0000d6ad0, 0xc00007a310, 0xc000001b00)
        /home/howard/main.go:14 +0x29
net.(*Resolver).dial(0xc00000e0a0, 0x53caa0, 0xc00007a300, 0x51a125, 0x3, 0xc0000183f0, 0xe, 0xc0000125c0, 0x0, 0x0, ...)
        /home/howard/go/src/net/lookup_unix.go:67 +0x226
net.(*Resolver).exchange(0xc00000e0a0, 0x53ca60, 0xc0000180e0, 0xc0000183f0, 0xe, 0x632e656c676f6f67, 0x2e6d6f, 0x0, 0x0, 0x0, ...)
        /home/howard/go/src/net/dnsclient_unix.go:144 +0x280
net.(*Resolver).tryOneName(0xc00000e0a0, 0x53ca60, 0xc0000180e0, 0xc00009e140, 0xc000018630, 0xb, 0x1c, 0x0, 0x0, 0x0, ...)
        /home/howard/go/src/net/dnsclient_unix.go:244 +0x325
net.(*Resolver).goLookupIPCNAMEOrder.func1(0xc00000e0a0, 0x53ca60, 0xc0000180e0, 0xc00009e140, 0xc0000125a0, 0xc00007a2a0, 0x1c)
        /home/howard/go/src/net/dnsclient_unix.go:584 +0x90
created by net.(*Resolver).goLookupIPCNAMEOrder
        /home/howard/go/src/net/dnsclient_unix.go:583 +0x285
exit status 2

What did you see instead?

On Windows, the snippet never touched the dialer function and successfully resolves the domain name:

[216.58.207.206]