Abstract hash function usage (#28138)

Refactor Hash interfaces and centralize hash function. This will allow
easier introduction of different hash function later on.

This forms the "no-op" part of the SHA256 enablement patch.

modules/git/repo.go

@@ -7,6 +7,7 @@ package git
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"net/url"
@@ -62,14 +63,40 @@ func IsRepoURLAccessible(ctx context.Context, url string) bool {
 	return err == nil
 }
 
+// GetObjectFormatOfRepo returns the hash type of a repository at a given path
+func GetObjectFormatOfRepo(ctx context.Context, repoPath string) (ObjectFormat, error) {
+	var stdout, stderr strings.Builder
+
+	err := NewCommand(ctx, "hash-object", "--stdin").Run(&RunOpts{
+		Dir:    repoPath,
+		Stdout: &stdout,
+		Stderr: &stderr,
+		Stdin:  &strings.Reader{},
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	if stderr.Len() > 0 {
+		return nil, errors.New(stderr.String())
+	}
+
+	h, err := IDFromString(strings.TrimRight(stdout.String(), "\n"))
+	if err != nil {
+		return nil, err
+	}
+
+	return h.Type(), nil
+}
+
 // InitRepository initializes a new Git repository.
-func InitRepository(ctx context.Context, repoPath string, bare bool) error {
+func InitRepository(ctx context.Context, repoPath string, bare bool, objectFormat ObjectFormat) error {
 	err := os.MkdirAll(repoPath, os.ModePerm)
 	if err != nil {
 		return err
 	}
 
-	cmd := NewCommand(ctx, "init")
+	cmd := NewCommand(ctx, "init", "--object-format").AddDynamicArguments(objectFormat.String())
 	if bare {
 		cmd.AddArguments("--bare")
 	}