Defaults to v1.11.x version, despite "go 1.12" in go.mod file

[msiebuhr]

When building, I get this message:

 !!    The go.mod file for this project does not specify a Go version
 !!    
 !!    Defaulting to go1.11.5
 !!    
 !!    For more details see: https://devcenter.heroku.com/articles/go-apps-with-modules#build-configuration
 !!    

Despite go.mod having the line go 1.12 in it.

Having to specify the same thing twice is a little weird to me.

[freeformz]

Our support for go modules predates the go tooling adding the go X.Y directive.

ATM, you will need to add a line like the following to get go1.12:

// +heroku goVersion go1.12

[jmorrell]

We are working to get support for the go version directive out soon

[freeformz]

A discussion on go-nuts started by @sowjumn indicates that the go directive in the go.mod file shouldn't be used for version selection. It's meant to indicate the version of the language features that are required by the code base. For example, if a breaking change were introduced in go1.13 a go 1.12 directive would in theory allow for the code base to be compiled with go1.13, but using go1.12's feature set. I'm unsure how the language maintainers are going to pull this off over time given each new version with incompatible changes adds to their maintenance complexity. Maybe they'll only support the previous version (go 1.12 when go1.13 comes out, then only go 1.13 when go1.14 comes out, etc)?

(cc @ianlancetaylor to validate my interpretation of his post)

So, given that, I'm not convinced that using the go directive in go.mod is a good idea, except for selecting the minimal major version to use when no other info is available.

Example: go1.13.1 is out and is the current default version we're using and the buildpack is used to compile code with a go 1.12 directive. We have two options:

1. Trust that go1.13.1 will DTRT and properly compile the code base with the go 1.12 features
2. Use the latest minor version of go1.12

The later seems safer to me. The former is the intended use case, at least as I understand what was written.

[ianlancetaylor]

Yes: the "go" directive in go.mod indicates the language version to use when compiling code. There is a lot more detail about how this is intended to work at golang/go#28221.

We will support all previous language versions. It's not as hard as you suggest. C and C++ compilers do this routinely, via command line options like GCC's -std=.

[freeformz]

So the go directive in the go.mod file is not for go version selection.

[msiebuhr]

I see. I'd still posit that having go 1.12 in the file should make the buildpack should definitely not pick Go 1.11.5.

The right solution would then be to run any Go >= 1.12 w. -lang=go1.12.

[edmorley]

I'd still posit that having go 1.12 in the file should make the buildpack should definitely not pick Go 1.11.5.

The right solution would then be to run any Go >= 1.12 w. -lang=go1.12

I've filed #378 for discussing this further.

[tomandersen]

Ran into this today, so it's still happening. I used the GOVERSION env variable set to 1.14.2 to get my app running.

Maybe the Heroku docs can make more of deal about setting GOVERSION in the env?

[axetroy]

I also got this issue

I found it has been closed, can someone tell me how to solve this?

[tomandersen]

Axetroy - In your Heroku app dashboard, go to settings, "Reveal Config Vars" then add one

GOVERSION with value 1.14.2 or whatever you need.

[axetroy]

@tomandersen I did n’t read your last comment carefully before I sent the comment, anyway, thank you ❤️