feat: Add automatic error comparison and type assertion fixes

[kakkoyun]

This is an attempt to add auto-fixes for error comparisons. By all means, I'm no expert on the topic. Please let me know what I don't know. I would love to have this functionality to fix large codebases. I'm all open to iterate on this an improve the implementation. I'm opening it as soon as the tests pass so it could be in a rather rough shape.

Changes

Enhance errorlint analyzer with automatic fixes for:

• Error comparisons using == and !=
• Type assertions on errors
• Error switches

Adds suggested fixes to:

• Replace direct error comparisons with errors.Is()
• Convert type assertions to use errors.As()
• Transform error switches to use errors.Is() and errors.As()

Includes new test cases and golden files to validate the new automatic fixing capabilities.

[kakkoyun]

cc @polyfloyd

[ccoVeille]

Please consider my review

[kakkoyun]

@ccoVeille Thanks for the review. It's greatly appreciated. I will check them in-depth as soon as possible.

[polyfloyd]

Thanks for this! I'm sure this will be useful to a lot of people :)

Major remark, but hopefully a minor fix:

err.(*MyError) is rewritten to errors.As(err, recv) where recv = new(MyError). This will not work, as the pointer bit is significant for the error type. new(MyError) does return a *MyError, but in order for errors.As to work it needs another pointer, so **MyError. Otherwise it will panic:

panic: errors: *target must be interface or implement error

Changing the rewrite rule to copy the type verbatim should be enough to fix this.

You can play with this example to get an idea for how this works:

package main

import (
	"errors"
	"fmt"
)

type MyError struct{}

func (*MyError) Error() string { return "*MyError" }

func main() {

	var err error = &MyError{}

	if me, ok := err.(*MyError); ok {
		fmt.Println(me)
	} else {
		fmt.Println("-")
	}

	me := new(*MyError)
	if errors.As(err, me) {
		fmt.Println(me)
	} else {
		fmt.Println("-")
	}
}

I have only looked at the test files now, I hopefully have some time to look over the code this weekend...

[ccoVeille]

I'm amazed by the amount of work you did, and tremendous use cases you thought about, handled, and hopefully covered by unit tests.

I made a small suggestion, feel free to ignore.

[kakkoyun]

@ccoVeille for the review and kind words. You made my day. I hope this will be useable and we (as Go community) benefit from it.

[ccoVeille]

You are welcome, please consider tagging one of your commit with Co-authored-by tag if you felt my contribution was valuable enough to be mentioned.

Adding something like this to your commit messages

Co-authored-by: ccoVeille <[email protected]>

For example

Commit message followed by a line feed then the Co-authored-by tag

Co-authored-by: ccoVeille <[email protected]>

https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors#creating-co-authored-commits-on-the-command-line