From 9d6355f4ad31686714f7aa05355267e0226aea9f Mon Sep 17 00:00:00 2001
From: Hidde Beydals <hello@hidde.co>
Date: Mon, 15 Apr 2019 13:51:16 +0200
Subject: [PATCH] Warn user about non-existing configured branch

When a user tried to configure Flux against an empty repository or a
branch that did not exist we would report a bogus status and left the
user confused.

This commit makes it possible to configure a branch that should be
checked for existence on creation of a new repository. In case there
is no HEAD found for this branch, it does not exist in git terms, and
we report back a meaningful error message to the user.

As a bonus we also use this configured branch when we create a tag for
our write check, so we do not touch anything the user has not told us
to.
---
 cmd/fluxd/main.go      |  2 +-
 git/operations.go      |  5 ++++-
 git/operations_test.go |  2 +-
 git/repo.go            | 27 ++++++++++++++++++++++++---
 4 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/cmd/fluxd/main.go b/cmd/fluxd/main.go
index 76304c243..497c3b557 100644
--- a/cmd/fluxd/main.go
+++ b/cmd/fluxd/main.go
@@ -485,7 +485,7 @@ func main() {
 		SkipMessage: *gitSkipMessage,
 	}
 
-	repo := git.NewRepo(gitRemote, git.PollInterval(*gitPollInterval), git.Timeout(*gitTimeout))
+	repo := git.NewRepo(gitRemote, git.PollInterval(*gitPollInterval), git.Timeout(*gitTimeout), git.Branch(*gitBranch))
 	{
 		shutdownWg.Add(1)
 		go func() {
diff --git a/git/operations.go b/git/operations.go
index 26419daed..8f841377d 100644
--- a/git/operations.go
+++ b/git/operations.go
@@ -78,9 +78,12 @@ func checkout(ctx context.Context, workingDir, ref string) error {
 // checkPush sanity-checks that we can write to the upstream repo
 // (being able to `clone` is an adequate check that we can read the
 // upstream).
-func checkPush(ctx context.Context, workingDir, upstream string) error {
+func checkPush(ctx context.Context, workingDir, upstream, branch string) error {
 	// --force just in case we fetched the tag from upstream when cloning
 	args := []string{"tag", "--force", CheckPushTag}
+	if branch != "" {
+		args = append(args, branch)
+	}
 	if err := execGitCmd(ctx, args, gitCmdConfig{dir: workingDir}); err != nil {
 		return errors.Wrap(err, "tag for write check")
 	}
diff --git a/git/operations_test.go b/git/operations_test.go
index af2919a0f..74fcedae7 100644
--- a/git/operations_test.go
+++ b/git/operations_test.go
@@ -213,7 +213,7 @@ func TestCheckPush(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	err = checkPush(context.Background(), working, upstreamDir)
+	err = checkPush(context.Background(), working, upstreamDir, "")
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/git/repo.go b/git/repo.go
index 5f104521d..f9ac0f611 100644
--- a/git/repo.go
+++ b/git/repo.go
@@ -2,6 +2,7 @@ package git
 
 import (
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"os"
 	"sync"
@@ -47,6 +48,7 @@ const (
 type Repo struct {
 	// As supplied to constructor
 	origin   Remote
+	branch   string
 	interval time.Duration
 	timeout  time.Duration
 	readonly bool
@@ -83,6 +85,12 @@ func (t Timeout) apply(r *Repo) {
 	r.timeout = time.Duration(t)
 }
 
+type Branch string
+
+func (b Branch) apply(r *Repo) {
+	r.branch = string(b)
+}
+
 var ReadOnly optionFunc = func(r *Repo) {
 	r.readonly = true
 }
@@ -261,10 +269,23 @@ func (r *Repo) step(bg context.Context) bool {
 		return false
 
 	case RepoCloned:
+		ctx, cancel := context.WithTimeout(bg, r.timeout)
+		defer cancel()
+
+		if r.branch != "" {
+			ok, err := refExists(ctx, dir, "refs/heads/"+r.branch)
+			if err != nil {
+				r.setUnready(RepoCloned, err)
+				return false
+			}
+			if !ok {
+				r.setUnready(RepoCloned, fmt.Errorf("configured branch '%s' does not exist", r.branch))
+				return false
+			}
+		}
+
 		if !r.readonly {
-			ctx, cancel := context.WithTimeout(bg, r.timeout)
-			err := checkPush(ctx, dir, url)
-			cancel()
+			err := checkPush(ctx, dir, url, r.branch)
 			if err != nil {
 				r.setUnready(RepoCloned, err)
 				return false