git: Introduce new ObjectID type

We're currently passing around object IDs as plain strings, making it
harder than necessary at times to see what a given thing actually
represents. To lay the foundation, this commit introduces a new ObjectID
which we can slowly migrate towards in the future to improve type
safety.

2 files changed, 73 insertions, 0 deletions

diff --git a/internal/git/id.go b/internal/git/id.go
index be07c4d79..e64942c73 100644
--- a/internal/git/id.go
+++ b/internal/git/id.go
@@ -14,6 +14,30 @@ var (
 	objectIDRegex = regexp.MustCompile(`\A[0-9a-f]{40}\z`)
 )
 
+// ObjectID represents an object ID.
+type ObjectID string
+
+// NewObjectIDFromHex constructs a new ObjectID from the given hex
+// representation of the object ID. Returns ErrInvalidObjectID if the given
+// OID is not valid.
+func NewObjectIDFromHex(hex string) (ObjectID, error) {
+	if err := ValidateObjectID(hex); err != nil {
+		return "", err
+	}
+	return ObjectID(hex), nil
+}
+
+// String returns the hex representation of the ObjectID.
+func (oid ObjectID) String() string {
+	return string(oid)
+}
+
+// Revision returns a revision of the ObjectID. This directly returns the hex
+// representation as every object ID is a valid revision.
+func (oid ObjectID) Revision() Revision {
+	return Revision(oid.String())
+}
+
 // ValidateObjectID checks if id is a syntactically correct object ID. Abbreviated
 // object IDs are not deemed to be valid. Returns an ErrInvalidObjectID if the
 // id is not valid.
diff --git a/internal/git/id_test.go b/internal/git/id_test.go
index 5bff91ac2..0ab6f0dd9 100644
--- a/internal/git/id_test.go
+++ b/internal/git/id_test.go
@@ -55,3 +55,52 @@ func TestValidateObjectID(t *testing.T) {
 		})
 	}
 }
+
+func TestNewObjectIDFromHex(t *testing.T) {
+	for _, tc := range []struct {
+		desc  string
+		oid   string
+		valid bool
+	}{
+		{
+			desc:  "valid object ID",
+			oid:   "356e7793f9654d51dfb27312a1464062bceb9fa3",
+			valid: true,
+		},
+		{
+			desc:  "object ID with non-hex characters fails",
+			oid:   "x56e7793f9654d51dfb27312a1464062bceb9fa3",
+			valid: false,
+		},
+		{
+			desc:  "object ID with upper-case letters fails",
+			oid:   "356E7793F9654D51DFB27312A1464062BCEB9FA3",
+			valid: false,
+		},
+		{
+			desc:  "too short object ID fails",
+			oid:   "356e7793f9654d51dfb27312a1464062bceb9fa",
+			valid: false,
+		},
+		{
+			desc:  "too long object ID fails",
+			oid:   "356e7793f9654d51dfb27312a1464062bceb9fa33",
+			valid: false,
+		},
+		{
+			desc:  "empty string fails",
+			oid:   "",
+			valid: false,
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			oid, err := NewObjectIDFromHex(tc.oid)
+			if tc.valid {
+				require.NoError(t, err)
+				require.Equal(t, tc.oid, oid.String())
+			} else {
+				require.Error(t, err)
+			}
+		})
+	}
+}