git2go: Implement support for subcommands

In order to keep the next commit focussed on actual merge logic, let's
prepare the infrastructure to support subcommands in the gitaly-git2go
binary.

2 files changed, 55 insertions, 11 deletions

diff --git a/cmd/gitaly-git2go/main.go b/cmd/gitaly-git2go/main.go
index bc25dc67c..cdd168482 100644
--- a/cmd/gitaly-git2go/main.go
+++ b/cmd/gitaly-git2go/main.go
@@ -3,23 +3,48 @@
 package main
 
 import (
+	"flag"
+	"fmt"
 	"os"
-
-	git "github.com/libgit2/git2go/v30"
 )
 
+type subcmd interface {
+	Flags() *flag.FlagSet
+	Run() error
+}
+
+var subcommands = map[string]subcmd{
+	"merge": &mergeSubcommand{},
+}
+
+const programName = "gitaly-git2go"
+
+func fatalf(format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, format+"\n", args...)
+	os.Exit(1)
+}
+
 func main() {
-	repo, err := git.OpenRepository(".")
-	if err != nil {
-		os.Exit(1)
+	flags := flag.NewFlagSet(programName, flag.ExitOnError)
+	flags.Parse(os.Args)
+
+	if flags.NArg() < 2 {
+		fatalf("missing subcommand")
+	}
+
+	subcmd, ok := subcommands[flags.Arg(1)]
+	if !ok {
+		fatalf("unknown subcommand: %q", flags.Arg(1))
 	}
-	defer repo.Free()
 
-	head, err := repo.Head()
-	if err != nil {
-		os.Exit(1)
+	subcmdFlags := subcmd.Flags()
+	subcmdFlags.Parse(flags.Args()[2:])
+
+	if subcmdFlags.NArg() != 0 {
+		fatalf("%s: trailing arguments", subcmdFlags.Name())
 	}
-	defer head.Free()
 
-	println(head.Target().String())
+	if err := subcmd.Run(); err != nil {
+		fatalf("%s: %s", subcmdFlags.Name(), err)
+	}
 }
diff --git a/cmd/gitaly-git2go/merge.go b/cmd/gitaly-git2go/merge.go
new file mode 100644
index 000000000..1d2f48c4b
--- /dev/null
+++ b/cmd/gitaly-git2go/merge.go
@@ -0,0 +1,19 @@
+// +build static,system_libgit2
+
+package main
+
+import (
+	"flag"
+)
+
+type mergeSubcommand struct {
+}
+
+func (cmd *mergeSubcommand) Flags() *flag.FlagSet {
+	flags := flag.NewFlagSet("merge", flag.ExitOnError)
+	return flags
+}
+
+func (cmd *mergeSubcommand) Run() error {
+	return nil
+}