Improve ObjectFormat interface (#28496)

The 4 functions are duplicated, especially as interface methods. I think
we just need to keep `MustID` the only one and remove other 3.

```
MustID(b []byte) ObjectID
MustIDFromString(s string) ObjectID
NewID(b []byte) (ObjectID, error)
NewIDFromString(s string) (ObjectID, error)
```

Introduced the new interfrace method `ComputeHash` which will replace
the interface `HasherInterface`. Now we don't need to keep two
interfaces.

Reintroduced `git.NewIDFromString` and `git.MustIDFromString`. The new
function will detect the hash length to decide which objectformat of it.
If it's 40, then it's SHA1. If it's 64, then it's SHA256. This will be
right if the commitID is a full one. So the parameter should be always a
full commit id.

@AdamMajer Please review.

1 files changed, 17 insertions, 20 deletions

diff --git a/modules/git/object_format.go b/modules/git/object_format.go
index ee7e659ed0..27771e7459 100644
--- a/modules/git/object_format.go
+++ b/modules/git/object_format.go
@@ -6,6 +6,7 @@ package git
 import (
 	"crypto/sha1"
 	"regexp"
+	"strconv"
 )
 
 // sha1Pattern can be used to determine if a string is an valid sha
@@ -20,14 +21,12 @@ type ObjectFormat interface {
 	EmptyTree() ObjectID
 	// FullLength is the length of the hash's hex string
 	FullLength() int
-
+	// IsValid returns true if the input is a valid hash
 	IsValid(input string) bool
+	// MustID creates a new ObjectID from a byte slice
 	MustID(b []byte) ObjectID
-	MustIDFromString(s string) ObjectID
-	NewID(b []byte) (ObjectID, error)
-	NewIDFromString(s string) (ObjectID, error)
-
-	NewHasher() HasherInterface
+	// ComputeHash compute the hash for a given ObjectType and content
+	ComputeHash(t ObjectType, content []byte) ObjectID
 }
 
 type Sha1ObjectFormatImpl struct{}
@@ -59,20 +58,18 @@ func (Sha1ObjectFormatImpl) MustID(b []byte) ObjectID {
 	return &id
 }
 
-func (h Sha1ObjectFormatImpl) MustIDFromString(s string) ObjectID {
-	return MustIDFromString(h, s)
-}
-
-func (h Sha1ObjectFormatImpl) NewID(b []byte) (ObjectID, error) {
-	return IDFromRaw(h, b)
-}
-
-func (h Sha1ObjectFormatImpl) NewIDFromString(s string) (ObjectID, error) {
-	return genericIDFromString(h, s)
-}
-
-func (h Sha1ObjectFormatImpl) NewHasher() HasherInterface {
-	return &Sha1Hasher{sha1.New()}
+// ComputeHash compute the hash for a given ObjectType and content
+func (h Sha1ObjectFormatImpl) ComputeHash(t ObjectType, content []byte) ObjectID {
+	hasher := sha1.New()
+	_, _ = hasher.Write(t.Bytes())
+	_, _ = hasher.Write([]byte(" "))
+	_, _ = hasher.Write([]byte(strconv.FormatInt(int64(len(content)), 10)))
+	_, _ = hasher.Write([]byte{0})
+
+	// HashSum generates a SHA1 for the provided hash
+	var sha1 Sha1Hash
+	copy(sha1[:], hasher.Sum(nil))
+	return &sha1
 }
 
 var Sha1ObjectFormat ObjectFormat = Sha1ObjectFormatImpl{}