Use VERSION file to detect version as fallback

This ensures a proper version is generated in the event of
building from non-git source.

- Attempt existing detection from git
- Attempt to read `VERSION` (`../VERSION` when in `_build/`)
- If both fail, use `unknown`

Refact `GitalyMake::VersionPrefixed` to make to call
`gm.VersionFromGit`, if that returns `unknown`, call
`gm.VersionFromFile`, and return whatever that does.

`VersionFromGit` takes the original functionality of `VersionPrefixed`,
and `VersionFromFile` looks for `../VERSION` file.

2 files changed, 27 insertions, 5 deletions

diff --git a/_support/makegen.go b/_support/makegen.go
index c381b149b..f4685760a 100644
--- a/_support/makegen.go
+++ b/_support/makegen.go
@@ -145,21 +145,38 @@ func (gm *gitalyMake) GoLdFlags() string {
 	return fmt.Sprintf("-ldflags '-X %s/internal/version.version=%s -X %s/internal/version.buildtime=%s'", gm.Pkg(), gm.Version(), gm.Pkg(), gm.BuildTime())
 }
 
-func (gm *gitalyMake) VersionPrefixed() string {
-	if len(gm.versionPrefixed) > 0 {
-		return gm.versionPrefixed
+func (gm *gitalyMake) VersionFromFile() string {
+	data, err := ioutil.ReadFile("../VERSION")
+	if err != nil {
+		log.Printf("Error: %v", err)
+		log.Printf("Unable to obtain version from VERSION file.")
+		return "unknown"
 	}
+	return fmt.Sprintf("v%s",strings.TrimSpace(string(data)))
+}
 
+func (gm *gitalyMake) VersionFromGit() string {
 	cmd := exec.Command("git", "describe")
 	cmd.Stderr = os.Stderr
 	out, err := cmd.Output()
 	if err != nil {
 		log.Printf("%s: %v", strings.Join(cmd.Args, " "), err)
-		gm.versionPrefixed = "unknown"
+		return "unknown"
+	}
+	return strings.TrimSpace(string(out))
+}
+
+func (gm *gitalyMake) VersionPrefixed() string {
+	if len(gm.versionPrefixed) > 0 {
 		return gm.versionPrefixed
 	}
-	gm.versionPrefixed = strings.TrimSpace(string(out))
 
+	version := gm.VersionFromGit()
+	if version == "unknown" {
+		log.Printf("Unable to determine version from Git. Attempting VERSION file")
+		version = gm.VersionFromFile()
+	}
+	gm.versionPrefixed = version
 	return gm.versionPrefixed
 }
 
diff --git a/changelogs/unreleased/1365-version-fallback-file.yml b/changelogs/unreleased/1365-version-fallback-file.yml
new file mode 100644
index 000000000..3f0080715
--- /dev/null
+++ b/changelogs/unreleased/1365-version-fallback-file.yml
@@ -0,0 +1,5 @@
+---
+title: Allow version detection from file, if git fails
+merge_request: 1056
+author:
+type: fixed