[Go] Add go.mod file

[le-michael]

This will help the go cli and editors understand which directory is relevant to our go library.

Migration to go modules is recommended by the go team since version 1.16. See, https://github.com/golang/go/wiki/Modules

Note:
This change will also set the minimum version of go to be latest version (1.19) in order to use this library. That means clients using an older version of go will be required to upgrade their project.

We can reduce the minimum version to an older release if we see an issue with this.

[ceejatec]

This go.mod file is incorrect, isn't it? It specifies the module name as "github.com/google/flatbuffers", but the module name in all documentation is "github.com/google/flatbuffers/go". eg.

https://pkg.go.dev/github.com/google/flatbuffers/go
https://google.github.io/flatbuffers/flatbuffers_guide_use_go.html

With this new go.mod file in place, now previously-working code is breaking with errors like

github.com/google/flatbuffers/go: github.com/google/flatbuffers/go@v0.0.0-20230104045611-6420fa5c8856: parsing go.mod:
module declares its path as: github.com/google/flatbuffers
    but was required as: github.com/google/flatbuffers/go

[le-michael]

This go.mod file is incorrect, isn't it? It specifies the module name as "github.com/google/flatbuffers", but the module name in all documentation is "github.com/google/flatbuffers/go". eg.

You're right. Sent out a fix at #7756. Thanks for reporting this!

[ceejatec]

Thanks!

[WineChord]

@le-michael a tag prefixed with "go" must be provided such as "go/v0.1.0" or else automatic module finding by go mod tidy will consistently result in "ambiguous import":

xxx imports
            github.com/google/flatbuffers/go: ambiguous import: found package github.com/google/flatbuffers/go in multiple modules:
            github.com/google/flatbuffers v2.0.6+incompatible (/root/go/pkg/mod/github.com/google/flatbuffers@v2.0.6+incompatible/go)
            github.com/google/flatbuffers/go v0.0.0-20230104232246-af9ceabeef1a (/root/go/pkg/mod/github.com/google/flatbuffers/go@v0.0.0-20230104232246-af9ceabeef1a)

[le-michael]

It seems that after introducing the go.mod we're exporting two modules for flatbuffers now on pkg.go.dev.

https://pkg.go.dev/github.com/google/flatbuffers
and
https://pkg.go.dev/github.com/google/flatbuffers/go

The former has the correct version history and version on release while the latter is the new module and has an auto generated version derived from the version tag and commit id. Ideally, we'd want to introduce the go.mod file in the root directory of this repository to maintain the version history for existing clients but that will lead to the language server with being polluted with suggestions from our test files.

I think we may have to revert this change to prevent the version history of our package on go.dev from getting messier and reintroduce the go.mod file in a future PR once we figure to correct location to install it.

[vitaly-eureka-security]

In the last several days we are consistently getting

github.com/google/flatbuffers/go: ambiguous import: found package github.com/google/flatbuffers/go in multiple modules:
	github.com/google/flatbuffers v22.11.23+incompatible (/home/runner/go/pkg/mod/github.com/google/flatbuffers@v22.11.23+incompatible/go)
	github.com/google/flatbuffers/go v0.0.0-20230110200425-62e4d2e5b215 (/home/runner/go/pkg/mod/github.com/google/flatbuffers/go@v0.0.0-20230110200425-62e4d2e5b215)

when trying to update dependencies with go get.

Seems to be related to the double export in pkg.go.dev.

[le-michael]

@vitaly-eureka-security can you try removing the github.com/google/flatbuffers dependency from your go.mod file then run go mod tidy to install the new github.com/google/flatbuffers/go dependency?

You should be able to update the dependency using go get -u github.com/google/flatbuffers/go after doing that.

We're planning to leave the go.mod file as is and we will start tagging the go subdirectory so that the module version matches the flatbuffer release version.

[vitaly-eureka-security]

@vitaly-eureka-security can you try removing the github.com/google/flatbuffers dependency from your go.mod file then run go mod tidy to install the new github.com/google/flatbuffers/go dependency?

You should be able to update the dependency using go get -u github.com/google/flatbuffers/go after doing that.

We're planning to leave the go.mod file as is and we will start tagging the go subdirectory so that the module version matches the flatbuffer release version.

@le-michael - thanks for the reply. I followed the instructions and removed the dependency.
Running go mod tidy resulted in bringing the dependency back (it is indirect dependency we receive from apache arrow):

$ go mod tidy
go: downloading github.com/google/flatbuffers v2.0.8+incompatible

Running go get -u ./... afterwards resulted in:

$ go get -u ./...
github.com/<module> imports
        github.com/snowflakedb/gosnowflake imports
        github.com/apache/arrow/go/arrow/ipc imports
        github.com/google/flatbuffers/go: ambiguous import: found package github.com/google/flatbuffers/go in multiple modules:
        github.com/google/flatbuffers v2.0.8+incompatible (<path>\go\pkg\mod\github.com\google\flatbuffers@v2.0.8+incompatible\go)
        github.com/google/flatbuffers/go v0.0.0-20230110200425-62e4d2e5b215 (<path>\go\pkg\mod\github.com\google\flatbuffers\go@v0.0.0-20230110200425-62e4d2e5b215)

[le-michael]

@vitaly-eureka-security I opened up an issue #7780 we can continue the discussion there.

[le-michael]

@vitaly-eureka-security should be fixed now. Please let me know if it's still broken.

[vitaly-eureka-security]

@vitaly-eureka-security should be fixed now. Please let me know if it's still broken.

Thanks @le-michael - works like a charm!