[parsing/mfm] Rework codeblock node parsing & serialization

Iceshrimp.Backend/Core/Helpers/LibMfm/Serialization/MfmSerializer.cs

@@ -17,7 +17,7 @@ public static class MfmSerializer
 				{
 					result.Append($"\n```{mfmCodeBlockNode.Language?.Value ?? ""}\n");
 					result.Append(mfmCodeBlockNode.Code);
-					result.Append("\n```\n\n");
+					result.Append("\n```\n");
 					break;
 				}
 				case MfmMathBlockNode mfmMathBlockNode:

Iceshrimp.Parsing/Mfm.fs

@@ -202,13 +202,15 @@ module private MfmParser =
         |>> fun v -> MfmInlineCodeNode(v) :> MfmNode
 
     let codeBlockNode =
-        opt (previousCharSatisfies isNewline >>. skipNewline)
+        opt skipNewline
+        >>. opt skipNewline
         >>. previousCharSatisfiesNot isNotNewline
         >>. skipString "```"
         >>. opt (many1CharsTill asciiLetter (lookAhead newline))
         .>>. (skipNewline
               >>. manyCharsTill anyChar (attempt (skipNewline >>. skipString "```")))
-        .>> (opt <| attempt (skipNewline >>. skipNewline))
+        .>> (skipNewline <|> eof)
+        .>> opt skipNewline
         |>> fun (lang: string option, code: string) -> MfmCodeBlockNode(code, lang) :> MfmNode
 
     let mathNode =

Iceshrimp.Tests/Parsing/MfmTests.cs

@@ -140,7 +140,15 @@ public class MfmTests
 	[TestMethod]
 	public void TestCodeBlock()
 	{
-		const string input = """
+		const string canonical = """
+		                         test 123
+		                         ```
+		                         this is a code block
+		                         ```
+		                         test 123
+		                         """;
+
+		const string alt = """
 		                   test 123
 
 		                   ```
@@ -149,17 +157,21 @@ public class MfmTests
 
 		                   test 123
 		                   """;
+
 		List<MfmNode> expected =
 		[
-			new MfmTextNode("test 123\n"),
+			new MfmTextNode("test 123"),
 			new MfmCodeBlockNode("this is a code block", null),
 			new MfmTextNode("test 123")
 		];
-		var res = Mfm.parse(input);
+		var res  = Mfm.parse(canonical);
+		var res2 = Mfm.parse(alt);
 
 		AssertionOptions.FormattingOptions.MaxDepth = 100;
 		res.ToList().Should().Equal(expected, MfmNodeEqual);
-		MfmSerializer.Serialize(res).Should().BeEquivalentTo(input);
+		res2.ToList().Should().Equal(expected, MfmNodeEqual);
+		MfmSerializer.Serialize(res).Should().BeEquivalentTo(canonical);
+		MfmSerializer.Serialize(res2).Should().BeEquivalentTo(canonical);
 	}
 
 	[TestMethod]