Clean up build stuff

[cpuguy83]

1. Uses modern go in Dockerfile
2. Fix make build pre-reqs
3. Remove interim BUILDFLAGS handling
4. Remove vendor dir (which was unused)
5. passthrough buildkit platform vars
6. parse buildkit vars in makefile

[thaJeztah]

Can't comment on the lines above, but if we're cleaning up;

• LINTER_BIN looks unused
• perhaps change GO111MODULE default to auto

[cpuguy83]

No this needs go modules. We need to make sure its own regardless of if we are in gopath or not.

[thaJeztah]

Hm... looks like it's ignoring the vendor directory.

rm -rf bin && docker run --rm -e GO111MODULE=auto -e CGO_ENABLED=0 -v $(pwd):/app -w /app golang:1.17 sh -c 'go build -o bin/go-md2man && bin/go-md2man --foobar'
go: downloading github.com/russross/blackfriday/v2 v2.1.0
flag provided but not defined: -foobar

rm -rf bin && docker run --rm -e GO111MODULE=on -e CGO_ENABLED=0 -v $(pwd):/app -w /app golang:1.17 sh -c 'go build -o bin/go-md2man && bin/go-md2man --foobar'
go: downloading github.com/russross/blackfriday/v2 v2.1.0
flag provided but not defined: -foobar

rm -rf bin && docker run --rm -e GO111MODULE=auto -e CGO_ENABLED=0 -v $(pwd):/go/src/github.com/cpuguy83/go-md2man -w /go/src/github.com/cpuguy83/go-md2man golang:1.17 bash -c 'go build -o bin/go-md2man && bin/go-md2man --foobar'
go: downloading github.com/russross/blackfriday/v2 v2.1.0
flag provided but not defined: -foobar

rm -rf bin && docker run --rm -e GO111MODULE=on -e CGO_ENABLED=0 -v $(pwd):/go/src/github.com/cpuguy83/go-md2man -w /go/src/github.com/cpuguy83/go-md2man golang:1.17 bash -c 'go build -o bin/go-md2man && bin/go-md2man --foobar'
go: downloading github.com/russross/blackfriday/v2 v2.1.0
flag provided but not defined: -foobar

So looks like all permutations ignore vendor and will download the module. Disabling networking shows that's indeed the case;

rm -rf bin && docker run --rm -e GO111MODULE=on --network=none -e CGO_ENABLED=0 -v $(pwd):/go/src/github.com/cpuguy83/go-md2man -w /go/src/github.com/cpuguy83/go-md2man golang:1.17 bash -c 'go build -o bin/go-md2man && bin/go-md2man --foobar'
go: github.com/russross/blackfriday/v2@v2.1.0: Get "https://proxy.golang.org/github.com/russross/blackfriday/v2/@v/v2.1.0.mod": dial tcp: lookup proxy.golang.org on 192.168.65.5:53: dial udp 192.168.65.5:53: connect: network is unreachable
go: downloading github.com/russross/blackfriday/v2 v2.1.0
go: github.com/russross/blackfriday/v2@v2.1.0: Get "https://proxy.golang.org/github.com/russross/blackfriday/v2/@v/v2.1.0.mod": dial tcp: lookup proxy.golang.org on 192.168.65.5:53: dial udp 192.168.65.5:53: connect: network is unreachable

The only option that works is to use -mod=vendor:

rm -rf bin && docker run --rm -e GO111MODULE=on --network=none -e CGO_ENABLED=0 -v $(pwd):/go/src/github.com/cpuguy83/go-md2man -w /go/src/github.com/cpuguy83/go-md2man golang:1.17 bash -c 'go build -mod=vendor -o bin/go-md2man && bin/go-md2man --foobar'

flag provided but not defined: -foobar
Usage of bin/go-md2man:

[cpuguy83]

Right yes, vendor is leftover from go mod transition...

[cpuguy83]

Removed vendor dir.

[cpuguy83]

Added go1.11 to the test matrix.
Intentionally keeping older go because this is picked up in distro packages.