Re: [PATCH] persistent-https: add go.mod to fix compile

Dominyk Tiller [off-list ref] writes:

Junio C Hamano wrote on 30/03/2021 20:09:

quoted

"Dominyk Tiller via GitGitGadget" [off-list ref] writes:

quoted

From: Dominyk Tiller <redacted>

GOPATH-based builds and non module-aware builds are being deprecated
by golang upstream, which currently causes this to fail. This adds a
barebones mod file to fix the build.

The `persistent-https` code hasn't been touched for a long time but
I assume this is preferable to simply removing it from the codebase.

Before this change:

case $(go version) in \
	"go version go"1.[0-5].*) EQ=" " ;; *) EQ="=" ;; esac && \
	go build -o git-remote-persistent-https \
		-ldflags "-X main._BUILD_EMBED_LABEL${EQ}"
go: cannot find main module, but found .git/config in ../git
	to create a module there, run:
	cd ../.. && go mod init
make: *** [git-remote-persistent-https] Error 1

With which version of go?  Any recent version would fail the same
way, or only 1.16 and later?

The link I referenced in the notes explains a little more in depth, but
there's an environment variable you can use with 1.16 to temporarily
mitigate the failure, i.e. `export GO111MODULE=off`, but regardless of
the presence of that the lack of module-awareness will become a hard
failure in Go 1.17. The lack of module awareness is only a failure on Go
1.16 and later. Module support was added in basic form as far back as Go
1.11, released late 2018.

quoted

quoted

Ref: https://blog.golang.org/go116-module-changes.

diff --git a/contrib/persistent-https/go.mod b/contrib/persistent-https/go.mod
new file mode 100644
index 000000000000..6028b1fe5e62
--- /dev/null
+++ b/contrib/persistent-https/go.mod

@@ -0,0 +1,3 @@
+module github.com/git/git/contrib/persistent-https
+
+go 1.16

Can I ask what is affected by this 1.16 version number?  Do the
users have to use 1.16 and nothing older or newer?

As a non Go user, I am trying to see if this change is "make it work
for all users of reasonably new versions of Go" (if that is the
case, what is the "reasonably new") or "make it work for those with
1.16, and everybody else should either install 1.16 or figure out 
their own solutions".

Thanks.

This is more thoroughly detailed here:
https://golang.org/ref/mod#go-mod-file-go, but essentially the version
number was/is intended to be the minimum Go version the module is
designed to work with. We could set it lower to play it safe if the Git
project wishes, but to date there have been no backwards
incompatibilities with the module system and the way we're using the
module system is so basic I don't see any way we'd trigger the
version-based behaviours detailed in the link above. For what it's worth
testing locally against 1.15 it builds without issue, despite being a
lower version number than specified in the string.

I've done the same experiment with 1.15 before writing the message
you are responding to.

It felt a bit of magic as I never expected 1.15 binary to anticipate
what is in 1.16, or to be able to say that a version from the future
(from 1.15 binary's point of view) has backward incompatible
semantics to stop the use of the module (the reason why I used 1.15
was because it was readily available in Debian).  Public
documentation by Go folks that explain go.mod file format seems to
use "go 1.12" in the examples everywhere, so it might be a sane
version string to use?

In any case, explaining these things in this response is good, but
eventually we need to make sure that the readers of the resulting
commit would not have to ask the same question, without having to
refer to external documentation.

Thanks.

On Tue, Mar 30, 2021 at 6:07 PM Junio C Hamano [off-list ref] wrote:

In any case, explaining these things in this response is good, but
eventually we need to make sure that the readers of the resulting
commit would not have to ask the same question, without having to
refer to external documentation.

It might also be worthwhile -- for the non-Go readers -- for the
commit message to mention that this addition of a `go.mod` file does
not hinder those stuck with old pre-module versions of Go (it doesn't
help them either, but that's less significant), thus this change does
not require them to update to a modern version of Go (i.e. we're not
raising the minimum required version).