git2go: Extract `lookupCommit` into its own file

The generic function `lookupCommit()` used to lookup a commit by
reference is currently implemented in "merge.go", which is also its only
user. As we're about to add additional users, let's extract this
function into a standalone file to help discoverability.

2 files changed, 28 insertions, 19 deletions

diff --git a/cmd/gitaly-git2go/merge.go b/cmd/gitaly-git2go/merge.go
index 3f07a51ab..dab99c4bc 100644
--- a/cmd/gitaly-git2go/merge.go
+++ b/cmd/gitaly-git2go/merge.go
@@ -23,25 +23,6 @@ func (cmd *mergeSubcommand) Flags() *flag.FlagSet {
 	return flags
 }
 
-func lookupCommit(repo *git.Repository, ref string) (*git.Commit, error) {
-	object, err := repo.RevparseSingle(ref)
-	if err != nil {
-		return nil, fmt.Errorf("could not lookup reference: %w", err)
-	}
-
-	peeled, err := object.Peel(git.ObjectCommit)
-	if err != nil {
-		return nil, fmt.Errorf("could not peel reference: %w", err)
-	}
-
-	commit, err := peeled.AsCommit()
-	if err != nil {
-		return nil, fmt.Errorf("could not cast to commit: %w", err)
-	}
-
-	return commit, nil
-}
-
 func sanitizeSignatureInfo(info string) string {
 	return strings.Map(func(r rune) rune {
 		switch r {
diff --git a/cmd/gitaly-git2go/util.go b/cmd/gitaly-git2go/util.go
new file mode 100644
index 000000000..d580582cd
--- /dev/null
+++ b/cmd/gitaly-git2go/util.go
@@ -0,0 +1,28 @@
+// +build static,system_libgit2
+
+package main
+
+import (
+	"fmt"
+
+	git "github.com/libgit2/git2go/v30"
+)
+
+func lookupCommit(repo *git.Repository, ref string) (*git.Commit, error) {
+	object, err := repo.RevparseSingle(ref)
+	if err != nil {
+		return nil, fmt.Errorf("could not lookup reference: %w", err)
+	}
+
+	peeled, err := object.Peel(git.ObjectCommit)
+	if err != nil {
+		return nil, fmt.Errorf("could not peel reference: %w", err)
+	}
+
+	commit, err := peeled.AsCommit()
+	if err != nil {
+		return nil, fmt.Errorf("could not cast to commit: %w", err)
+	}
+
+	return commit, nil
+}