git: change Commit#String format

This changes the string format of `Commit` to use an `@` separator
instead of `/`, and drops the usage of "HEAD" as a virtual named
reference for commits without a named pointer (e.g. a Git branch and/or
tag). Matching the (revision) format proposed in RFC-0005.

Signed-off-by: Hidde Beydals <[email protected]>

git/git.go

@@ -67,9 +67,9 @@ type Commit struct {
 // for a "tag-1" tag.
 func (c *Commit) String() string {
 	if short := strings.SplitAfterN(c.Reference, "/", 3); len(short) == 3 {
-		return fmt.Sprintf("%s/%s", short[2], c.Hash)
+		return fmt.Sprintf("%s@sha1:%s", short[2], c.Hash)
 	}
-	return fmt.Sprintf("HEAD/%s", c.Hash)
+	return fmt.Sprintf("sha1:%s", c.Hash)
 }
 
 // Verify the Signature of the commit with the given key rings.
@@ -121,8 +121,8 @@ var (
 )
 
 // IsConcreteCommit returns if a given commit is a concrete commit. Concrete
-// commits have most of commit metadata and commit content. In contrast, a
-// partial commit may only have some metadata and no commit content.
+// commits have most of the commit metadata and content. In contrast, a partial
+// commit may only have some metadata and no commit content.
 func IsConcreteCommit(c Commit) bool {
 	if c.Hash != nil && c.Encoded != nil {
 		return true

git/git_test.go

@@ -131,22 +131,22 @@ func TestCommit_String(t *testing.T) {
 				Hash:      []byte("commit"),
 				Reference: "refs/heads/main",
 			},
-			want: "main/commit",
+			want: "main@sha1:commit",
 		},
 		{
 			name: "Reference with slash and commit",
 			commit: &Commit{
 				Hash:      []byte("commit"),
 				Reference: "refs/heads/feature/branch",
 			},
-			want: "feature/branch/commit",
+			want: "feature/branch@sha1:commit",
 		},
 		{
-			name: "No reference",
+			name: "No name reference",
 			commit: &Commit{
 				Hash: []byte("commit"),
 			},
-			want: "HEAD/commit",
+			want: "sha1:commit",
 		},
 	}
 	for _, tt := range tests {