runtime: don't override user set commit and timestamp (#7549)

Signed-off-by: sspaink <sspaink@styra.com>

docs/content/extensions.md

@@ -382,7 +382,13 @@ set at build-time:
 These values can be set on the command-line when building OPA from source:
 
 ```
-go build -o opa++ -ldflags "-X github.com/open-policy-agent/opa/version.Version=MY_VERSION" main.go
+ go build \
+   -ldflags=" \
+   -X github.com/open-policy-agent/opa/v1/version.Version=MY_VERSION\
+   -X github.com/open-policy-agent/opa/v1/version.Vcs=MY_COMMIT_HASH \
+   -X github.com/open-policy-agent/opa/v1/version.Hostname=MY_HOSTNAME \
+   -X github.com/open-policy-agent/opa/v1/version.Timestamp=MY_TIMESTAMP" \
+   -o opa++
 ```
 
 ## Appendix

v1/version/version.go

@@ -31,18 +31,28 @@ func init() {
 	if !ok {
 		return
 	}
-	dirty := false
+	var dirty bool
+	var binTimestamp, binVcs string
+
 	for _, s := range bi.Settings {
 		switch s.Key {
 		case "vcs.time":
-			Timestamp = s.Value
+			binTimestamp = s.Value
 		case "vcs.revision":
-			Vcs = s.Value
+			binVcs = s.Value
 		case "vcs.modified":
 			dirty = s.Value == "true"
 		}
 	}
-	if dirty {
-		Vcs += "-dirty"
+
+	if Timestamp == "" {
+		Timestamp = binTimestamp
+	}
+
+	if Vcs == "" {
+		Vcs = binVcs
+		if dirty {
+			Vcs += "-dirty"
+		}
 	}
 }