Add go.mod

[methane]

Issue description

I have not used Go mod yet.

How should we do in v1.5 for better go mod support?

[julienschmidt]

Nothing. go modules are for dependency management. For now, we don't have any.
All we need is proper semantic versioning tags.

[taoso]

Nothing. go modules are for dependency management. For now, we don't have any.

@julienschmidt the google.golang.org/appengine/cloudsql is required.

mysql/appengine.go

Line 17 in 8f4b98d

"google.golang.org/appengine/cloudsql"

[julienschmidt]

The file has a build flag: +appengine.
I assume it only builds when this package is available anyway.

We're certainly not going to start forcing everyone to fetch a copy of couldsql.

[taoso]

@julienschmidt

The file has a build flag: +appengine.
However, if you use go-sql-driver in your go mod enabled project, your go.mod file will get the following line

github.com/go-sql-driver/mysql v1.4.1
...
google.golang.org/appengine v1.5.0 // indirect

It is weird. The google.golang.org/appengine is not always needed.

[taoso]

@julienschmidt is it really needed to shift the the cloudsql registration?

mysql/appengine.go

Lines 21 to 24 in 8f4b98d

	RegisterDialContext("cloudsql", func(_ context.Context, instance string) (net.Conn, error) {
	// XXX: the cloudsql driver still does not export a Context-aware dialer.
	return cloudsql.Dial(instance)
	})

[methane]

"Starting October 1, 2019, new deployments using this version will not be available." -- https://cloud.google.com/appengine/docs/standard/go/

We can remove appengine.go, at least from 2019-10-01.

[alexedwards]

@julienschmidt

We're certainly not going to start forcing everyone to fetch a copy of couldsql.

But it is fetched whenever someone runs go mod tidy, and listed in the go.mod file even if it is never used. A minimal example:

// File: main.go
package main

import "database/sql"
import _ "github.com/go-sql-driver/mysql"

func main() {
	_, _ = sql.Open("mysql", "user:password@/dbname")
}

$ go clean -modcache
$ go mod init example.com
$ go mod tidy
go: downloading github.com/go-sql-driver/mysql v1.4.1
go: extracting github.com/go-sql-driver/mysql v1.4.1
go: downloading google.golang.org/appengine v1.6.2
go: extracting google.golang.org/appengine v1.6.2

$ cat go.mod
module example.com

go 1.13

require (
	github.com/go-sql-driver/mysql v1.4.1
	google.golang.org/appengine v1.6.2 // indirect
)

$ ls $GOPATH/pkg/mod/google.golang.org/appengine@v1.6.2/
aetest             datastore    LICENSE            search
appengine.go       delay        log                socket
...

[Delphier]

@julienschmidt Should support go.mod

[methane]

I will remove appengine.go after 2019-10-01. Please wait it.

[julienschmidt]

My plan would be to move the dialer into a separate package (github.com/go-sql-driver/cloudsql-dialer) which can be imported and registers the dialer when required.

[julienschmidt]

Also see https://github.com/go-sql-driver/mysql/blob/go-mod/go.mod
Unfortunately, that still pulls google.golang.org/appengine, even though it isn't listed as a requirement in the go.mod file.

[methane]

My plan would be to move the dialer into a separate package (github.com/go-sql-driver/cloudsql-dialer) which can be imported and registers the dialer when required.

I don't think it is worth enough:

• It affects only for GAE/Go 1.9 users, and it is breaking change for them.
• No one can deploy their app to GAE/Go 1.9 after 2019-10-01.