Allow to build with Go 1.17 and Go 1.16

[klingtnet]

Without Go 1.17 in the list of supported build tags the iofs package is
not importable in a Go 1.17 project. A minimal example can be found in
this playground. The example will show the following build error:

prog.go:9:5: module github.com/golang-migrate/migrate/v4@latest found
(v4.14.1), but does not contain package
github.com/golang-migrate/migrate/v4/source/iofs

[coveralls]

Pull Request Test Coverage Report for Build 1234022515

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 57.709%

---

Totals
Change from base Build 1223561164:	0.0%
Covered Lines:	3713
Relevant Lines:	6434

---

💛 - Coveralls

[dhui]

Weird, go1.16 should be sufficient since it means Go 1.16 onwards.
This might be an issue with modules which hasn't always played well with build constraints...

[klingtnet]

@dhui I might really be an issue with how Go Modules handles build tags. Go's build constraint documentation states:

• a term for each Go major release, through the current version:
  "go1.1" from Go version 1.1 onward, "go1.12" from Go 1.12, and so on.

But, I cannot import this source/iofs without specifying Go 1.17 explicitly. Here's a proof that the forked version builds fine:

$ make
CGO_ENABLED=0 go build -o inject -ldflags="-X main.Version=2.7.5-1-g1dcf197" ./cmd/inject
cmd/inject/inject.go:30:2: no required module provides package github.com/golang-migrate/migrate/v4/source/iofs; to add it:
        go get github.com/golang-migrate/migrate/v4/source/iofs
make: *** [Makefile:12: inject] Error 1
$ go mod edit -replace=github.com/golang-migrate/migrate/v4=github.com/spreadshirt/migrate/[email protected]
$ make
CGO_ENABLED=0 go build -o inject -ldflags="-X main.Version=2.7.5-1-g1dcf197" ./cmd/inject
go: updates to go.mod needed; to update it:
        go mod tidy
make: *** [Makefile:12: inject] Error 1
$ go mod tidy
$ git diff go.mod
diff --git a/go.mod b/go.mod
index 8d90c31..ffc54a1 100644
--- a/go.mod
+++ b/go.mod
@@ -76,3 +76,5 @@ require (
        gopkg.in/square/go-jose.v2 v2.6.0 // indirect
        gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )
+
+replace github.com/golang-migrate/migrate/v4 => github.com/spreadshirt/migrate/v4 v4.6.1-0.20210914142308-ccfdae602432
$ make
CGO_ENABLED=0 go build -o inject -ldflags="-X main.Version=2.7.5-1-g1dcf197" ./cmd/inject

I think we can close this and I need to raise an issue in the golang/go repository.

[dhui]

Closing since other versions (not v4.14.1) should work. See: golang/go#48397 (comment)