feat: embed, io/fs support

[johejo]

Is your feature request related to a problem? Please describe.

The next Go 1.16 will add official file system interface and file embedding.

golang/go#41190
/~https://github.com/golang/go/tree/master/src/io/fs

golang/go#41191
/~https://github.com/golang/go/tree/master/src/embed

It would be great if golang-migrate supports these as source.Driver.

It replaces statik, go-bindata, and pkger.
Of course, this does not mean that they cannot be used.

Describe the solution you'd like

Describe alternatives you've considered

Additional context

We will also need to use the build tag properly.

[dhui]

Thanks for sharing!

There's already support for a httpfs source (net/http/FileSystem), so we could do something similar for io/fs/FS.

I believe, if an io/fs/FS source driver existed, we wouldn't need an explicit embed driver.

We'll need to add a build constraint for go1.16 for the io/fs/FS source driver.

[johejo]

We will not be able to include this feature until Go 1.15 is no longer supported. #480
However, some users may want to use this feature, so I created an extra module.
/~https://github.com/johejo/golang-migrate-extra
This is based on #472 .

[dhui]

Re-opening and will revert the revert when Go 1.15 is no longer supported by migrate

[wkoszek]

@dhui @johejo Any way we (segmed.ai) can help here? We can provide 2 pairs of eyes to help with getting this support integrated, and also could help with testing. @Fenges

[dhui]

@wkoszek There's nothing anyone can do but wait for Go 1.15 to be not be officially supported e.g. when the old supported version of Go (1.16) has the io/fs package. Otherwise, people running migrate on older versions of Go will run into this issue

[philippta]

Possible workaround until Go 1.15 is no longer supported:

main.go
migrations/
  1_create_tables.up.sql
  1_create_tables.down.sql

import "github.com/golang-migrate/migrate/v4/source/httpfs"

//go:embed migrations
var migrations embed.FS

source, err := httpfs.New(http.FS(migrations), "migrations")
// migrate.NewInstance("httpfs", source, ...)

[prochac]

We should use build tags to support 1.16 features and keep the support for 1.15 at least until 1.17 is released
(Following https://golang.org/doc/devel/release.html#policy)

Take an example from here:
/~https://github.com/pkg/errors/blob/master/go113.go

[dhui]

The PR that added support for io/fs had build constraints but modules ignore built constraints. See: #480 (comment)

[ivanduka]

Possible workaround until Go 1.15 is no longer supported:

main.go
migrations/
  1_create_tables.up.sql
  1_create_tables.down.sql

import "github.com/golang-migrate/migrate/v4/source/httpfs"

//go:embed migrations
var migrations embed.FS

source, err := httpfs.New(http.FS(migrations), "migrations")
// migrate.NewInstance("httpfs", source, ...)

Thank you so much!
Small correction: we need to use NewWithSourceInstance instead of NewInstance in migrate.NewInstance("httpfs", source, ...)

[zikaeroh]

Go 1.16.2 and Go 1.15.10 (which were just released) include a fix for golang/go#44557, meaning that io/fs and embed can be depended on and not break downstream users when they go mod tidy (so long as they update their tooling to these latest patch releases), so this should be unblocked whenever you feel like those patch releases have been out long enough.

[vtolstov]

any chance to get embed support in golang-migrate ?

[dhui]

Let's wait a bit more time (about a month or two) for the newer versions of Go to be adopted. Your other option is to fork this library and merge the PR into your fork.

[alovak]

Did we wait enough time? :)

[alovak]

https://groups.google.com/g/golang-announce/c/cu9SP4eSXMc?pli=1

We have just released Go versions 1.16.4 and 1.15.12, minor point releases.
This minor release includes a security fix according to the new security policy (#44918).

1.15.12 is already here!

P.S. just to support my previous comment :)

[vtolstov]

i think that we wait enough. embed stuff not changed and not contains any bugs

[philippta]

What about using build tag for this, that restricts the compilation to Go 1.16 and onwards?

[dhui]

Fixed by #560
This io/fs support is now available in the master branch but won't be available in a release until CI works for releases again