[git-object] Encode empty tags like git does

git-object/src/tag/decode.rs

@@ -53,7 +53,8 @@ pub fn message<'a, E: ParseError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], (&
     let (i, _) = tag(NL)(i)?;
     fn all_to_end<'a, E: ParseError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], (&'a [u8], &'a [u8]), E> {
         if i.is_empty() {
-            return Err(nom::Err::Error(E::from_error_kind(i, nom::error::ErrorKind::Eof)));
+            // Empty message. That's OK.
+            return Ok((&[], (&[], &[])));
         }
         // an empty signature message signals that there is none - the function signature is needed
         // to work with 'alt(…)'. PGP signatures are never empty

git-object/src/tag/write.rs

@@ -29,8 +29,8 @@ impl crate::WriteTo for Tag {
             encode::trusted_header_signature(b"tagger", &tagger.to_ref(), &mut out)?;
         }
 
+        out.write_all(NL)?;
         if !self.message.is_empty() {
-            out.write_all(NL)?;
             out.write_all(&self.message)?;
         }
         if let Some(ref message) = self.pgp_signature {
@@ -49,11 +49,7 @@ impl crate::WriteTo for Tag {
                 .as_ref()
                 .map(|t| b"tagger".len() + 1 /* space */ + t.size() + 1 /* nl */)
                 .unwrap_or(0)
-            + if self.message.is_empty() {
-                0
-            } else {
-                1 /* nl */ + self.message.len()
-            }
+            + 1 /* nl */ + self.message.len()
             + self.pgp_signature.as_ref().map(|m| 1 /* nl */ + m.len() ).unwrap_or(0)
     }
 
@@ -71,8 +67,8 @@ impl<'a> crate::WriteTo for TagRef<'a> {
             encode::trusted_header_signature(b"tagger", tagger, &mut out)?;
         }
 
+        out.write_all(NL)?;
         if !self.message.is_empty() {
-            out.write_all(NL)?;
             out.write_all(self.message)?;
         }
         if let Some(message) = self.pgp_signature {
@@ -91,11 +87,7 @@ impl<'a> crate::WriteTo for TagRef<'a> {
                 .as_ref()
                 .map(|t| b"tagger".len() + 1 /* space */ + t.size() + 1 /* nl */)
                 .unwrap_or(0)
-            + if self.message.is_empty() {
-                0
-            } else {
-                1 /* nl */ + self.message.len()
-            }
+            + 1 /* nl */ + self.message.len()
             + self.pgp_signature.as_ref().map(|m| 1 /* nl */ + m.len()).unwrap_or(0)
     }
 

git-object/tests/fixtures/tag/empty.txt

@@ -2,3 +2,4 @@ object 01dd4e2a978a9f5bd773dae6da7aa4a5ac1cdbbc
 type commit
 tag empty
 tagger Sebastian Thiel <sebastian.thiel@icloud.com> 1592381636 +0800
+

git-object/tests/immutable/tag.rs

@@ -37,6 +37,10 @@ mod iter {
                 Token::TargetKind(Kind::Commit),
                 Token::Name(b"empty".as_bstr()),
                 Token::Tagger(tagger),
+                Token::Body {
+                    message: b"".as_bstr(),
+                    pgp_signature: None,
+                }
             ]
         );
         assert_eq!(tag_iter.target_id()?, target_id);
@@ -103,7 +107,7 @@ KLMHist5yj0sw1E4hDTyQa0=
     #[test]
     fn error_handling() -> crate::Result {
         let data = fixture_bytes("tag", "empty.txt");
-        let iter = TagRefIter::from_bytes(&data[..data.len() / 2]);
+        let iter = TagRefIter::from_bytes(&data[..data.len() / 3]);
         let tokens = iter.collect::<Vec<_>>();
         assert!(
             tokens.last().expect("at least the errored token").is_err(),