From 9f6d8645301d1c082b507475b9eb8142901abaa0 Mon Sep 17 00:00:00 2001
From: Christophe Fergeau <cfergeau@redhat.com>
Date: Wed, 15 Nov 2023 12:08:10 +0100
Subject: [PATCH] version: Add versioning for github tarballs

When building from github tarballs, getting the version from `git
describe` won't work, or worse, will be irrelevant [1]
However, we can make use of $Format$ and .gitattributes as described in
[2] to automatically substitute the correct version in a go variable
when `git archive` is used.
In particular, the correct version number will automatically be
substituted when GitHub creates releass tarballs.

[1] rpms/gvisor-tap-vsock.spec uses `%autosetup -Sgit -n %{name}-%{version}` which unpacks
the release tarball in a newly created git repository.

[2] https://icinga.com/blog/2022/05/25/embedding-git-commit-information-in-go-binaries/

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
---
 .gitattributes            |  1 +
 pkg/types/version.go      | 12 +++++++++++-
 rpm/gvisor-tap-vsock.spec |  4 ++--
 3 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 .gitattributes

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 000000000..d1273eaf9
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+/pkg/types/version.go export-subst
diff --git a/pkg/types/version.go b/pkg/types/version.go
index 8e2ea6d94..805c36bcd 100644
--- a/pkg/types/version.go
+++ b/pkg/types/version.go
@@ -4,9 +4,16 @@ import (
 	"flag"
 	"fmt"
 	"runtime/debug"
+	"strings"
 )
 
-var ModuleVersion = ""
+var (
+	// set using the '-X github.com/containers/gvisor-tap-vsock/pkg/types.ModuleVersion' linker flag
+	ModuleVersion = ""
+	// set through .gitattributes when `git archive` is used
+	// see https://icinga.com/blog/2022/05/25/embedding-git-commit-information-in-go-binaries/
+	gitArchiveVersion = "$Format:%(describe)$"
+)
 
 type version struct {
 	binaryName  string
@@ -33,6 +40,9 @@ func (ver *version) ShowVersion() bool {
 
 func moduleVersion() string {
 	switch {
+	// This will be substituted when building from a GitHub tarball
+	case !strings.HasPrefix(gitArchiveVersion, "$Format:"):
+		return gitArchiveVersion
 	// This will be set when building from git using make
 	case ModuleVersion != "":
 		return ModuleVersion
diff --git a/rpm/gvisor-tap-vsock.spec b/rpm/gvisor-tap-vsock.spec
index 2233b11f4..c691daebf 100644
--- a/rpm/gvisor-tap-vsock.spec
+++ b/rpm/gvisor-tap-vsock.spec
@@ -92,8 +92,8 @@ CGO_CFLAGS=$(echo $CGO_CFLAGS | sed 's/-specs=\/usr\/lib\/rpm\/redhat\/redhat-an
 export CGO_CFLAGS+=" -m64 -mtune=generic -fcf-protection=full"
 %endif
 
-# reset LDFLAGS for plugins and gvisor binaries, but ensure gvproxy --version and such is set
-LDFLAGS="-X github.com/containers/gvisor-tap-vsock/pkg/types.PackageVersion=%{version}"
+# reset LDFLAGS for plugins and gvisor binaries
+LDFLAGS=''
 
 # build gvisor-tap-vsock binaries
 %gobuild -o bin/gvproxy ./cmd/gvproxy