fix: allow building with go1.21 or higher via GOTOOLCHAIN=auto

[jakobmoellerdev]

Since Go 1.21 one can supply a toolchain version string for the minimum required version of Go in their go.mod file (e.g. go 1.21.4). From practical point of view it makes no difference whether you declare your requirement as go 1.21 or go 1.21.0 in the go.mod file because in both cases any Go 1.21+ family toolchain will be able to build your project successfully. However, the former makes it impossible for 1.21 toolchains to automatically download a toolchain from e.g. 1.22 language family (via the means of the GOTOOLCHAIN variable), because "1.22" as a string literal doesn't denote a toolchain (while 1.22.0 does).

To reproduce a build environment like this, one can use the following adjustment to the existing Dockerfile:

# Build topolvm
FROM --platform=$BUILDPLATFORM golang:1.21-bullseye AS build-topolvm

ENV GOTOOLCHAIN=auto

# Get argument
ARG TOPOLVM_VERSION
ARG TARGETARCH

COPY . /workdir
WORKDIR /workdir

RUN touch pkg/lvmd/proto/*.go
RUN make build-topolvm TOPOLVM_VERSION=${TOPOLVM_VERSION} GOARCH=${TARGETARCH}

Examples in other projects:
grafana
syft
kubernetes

[toshipp]

I want to clarify the motivation.

First, as far as I know, go 1.21.11 can accept the language version in the go directive. (ref. golang/go#67235), So, we can build topolvm by the latest golang:1.21-bullseye.
I tested your reproducer, but could not get the compile error. I also tested with golang:1.21.10-bullseye, it failed, but with golang:1.21.11-bullseye it succeeded. I doubt your local image refers to some old 1.21 series.

Second, why do you want to use golang 1.21? Since we intended to use 1.22, we specified the version in Dockerfile and go.mod.

[jakobmoellerdev]

To be perfectly transparent, we have build systems in our org that have a decoupled lifecycle from our topolvm compilation and its impossibly hard to get them to upgrade to latest. Thats why I want to add this version despite this as our build systems will not be able to build topolvm for k8s 1.30 in the next few weeks otherwise. I am aware this is an edge case, but considering that topolvm is the only project I know that doesnt specify the z-stream in go1.22 in my ecosystem I thought pulling this in should be fine. If this is absolutely non acceptable to you, I will have to move the same in our midstream

[toshipp]

I understand your situation. We have just started to support k8s 1.30 by #928. In the PR, the go directive will be written as 1.22.0. If you can wait for the PR, I'd like to leave this to it.

[jakobmoellerdev]

LGTM, thanks for your feedback. Ill wait for 1.30 rebase