add NilThen api

[shynome]

add err2.NilThen method and support try.Out(error).Handle(&err) bind error to err

I don't know much about ziglang errdefer and defer, but these api can give us a similar experience in golang

func main() {
	var err error
	logger := slog.With()

	logger.Debug("add node")
	defer err2.NilThen(&err, func() {
		logger.Debug("add node successful")
	})
	defer err2.Handle(&err, func() { try.To(err) })

	try.To(AddNode())
}

I use the blow code now

package main

import (
	"github.com/lainio/err2/try"
	"github.com/shynome/err0"
	"golang.org/x/exp/slog"
)

func main() {
	var err error
	logger := slog.With()

	logger.Debug("add node")
	defer err0.NilThen(&err, func() {
		logger.Debug("add node successful")
	})
	defer err2.Handle(&err, func() { try.To(err) })

	try.To(AddNode())
}

func AddNode() error { return nil }

[shynome]

I found use defer err2.Handle(&err, func() { try.To(err) }) is more clearly

func main() {
	var err error
	logger := slog.With()

	logger.Debug("add node")
	defer err2.NilThen(&err, func() {
		logger.Debug("add node successful")
	})
	defer err2.Handle(&err, func() { try.To(err) })

	try.To(AddNode())
}

[lainio]

Good catch! That must be a bug (or something harder), which makes it a little bit weird because I made a test for that: TestHandle_NoError into err2. But in the test, those handlers are in a different order. The func(noerr bool) is the second one. Here is a playground to test it.

Back to the drawing board 😄

[lainio]

I found it and wrote a couple of new tests, plus the fix. Can I wait a day or two before releasing the fix, v0.9.41?

In the meanwhile, you can use the handler order trick or something else.

I would like to wait 24 hours if someone else finds something else.

Once again, thank you!

[shynome]

Ohhh, you have done it so quickly. 👍
Of course you can, that is good.

Thanks again for your good library

[shynome]

I have checked issue-18 branch, I found I call try.To(errors.New("new error")) in ErrorHandler after CheckHandler called, the top err is not changed, only when I add a more ErrorHandler the err will be changed

package main

import (
	"errors"
	"log"

	"github.com/lainio/err2"
	"github.com/lainio/err2/try"
)

func main() {
	var err error
	defer func() {
		log.Println("????????", err)
	}()
	defer err2.Handle(&err, func(noerr bool) {
		log.Println("noerr handle2", noerr, err)
	})
	defer err2.Handle(&err)

	// commnet the below code, you will see diffrent logout
	defer err2.Handle(&err, func(err error) error {
		log.Println("aaaaaaaaaaaa")
		return err
	})

	defer err2.Handle(&err, func(err error) error {
		try.To(errors.New("pppppppppppp"))
		return nil
	})

	// commnet the below code, you will see diffrent logout again
	defer err2.Handle(&err, func(noerr bool) {
		log.Println("noerr handle3", noerr, err)
	})

	try.To(errors.New("wwww"))
}

[lainio]

Thank you! Awesome that you have taken the time to test the branch already. Highly appreciated.

I have now added enough tests to find and fix the bug.

I haven't released the v0.9.41 yet because of some things to consider with the auto-migration scripts. The company I'm working with uses the err2 in code bases with hundreds of thousands of lines of Go code. So, automation is the only option. Trying to hit two birds with the one rock ;-)

Regarding the bug, you're pointing out with your example that the try.To function is not the proper one to use inside the err2.Handle handler.

Don't do this:

	...
	defer err2.Handle(&err, func(err error) error {
		defer err2.Handle(&err) //This line cannot WORK inside the previous error handler
		try.To(errors.New("pppppppppppp")) // Panics in middle of panicking!
		return nil
	})

It must be like this:

	...
	defer err2.Handle(&err, func(err error) error {
		return errors.New("pppppppppppp") // now we are just overwriting the err value
	})