[parsing] Further improve mention parser logic, add more tests

Iceshrimp.Parsing/Mfm.fs

@@ -134,24 +134,20 @@ module private MfmParser =
     let aggregateTextInline nodes =
         nodes |> aggregateText |> List.map (fun x -> x :?> MfmInlineNode)
 
-    let domainFirstComponent =
-        many1Chars (satisfy isAsciiLetter <|> satisfy isDigit <|> anyOf "_-")
-
     let domainComponent =
-        many1Chars (satisfy isAsciiLetter <|> satisfy isDigit <|> anyOf "._-")
+        many1Chars (
+            satisfy isAsciiLetterOrNumber
+            <|> pchar '_'
+            <|> attempt (
+                pchar '-'
+                .>> (previousCharSatisfies isAsciiLetterOrNumber
+                     <|> nextCharSatisfies isAsciiLetterOrNumber)
+            )
+        )
 
-    let domainStart = (satisfy isAsciiLetter <|> satisfy isDigit)
+    let domain =
-
+        domainComponent .>>. (many <| attempt (skipChar '.' >>. domainComponent))
-    let domainFull =
+        |>> fun (a, b) -> String.concat "." <| Seq.append [ a ] b
-        domainStart .>>. domainFirstComponent .>>. pchar '.' .>>. many1 domainComponent
-
-    let domainAggregate1 (a: char, b: string) = string a + b
-    let domainAggregate2 (a: char * string, b: char) = (domainAggregate1 a) + string b
-
-    let domainAggregate (x: (char * string) * char, y: string list) =
-        domainAggregate2 x + (String.concat "" y)
-
-    let domain = domainFull |>> domainAggregate
 
     let acct (user: string, host: string option) =
         match host with
@@ -230,7 +226,10 @@ module private MfmParser =
     let mentionNode =
         previousCharSatisfiesNot isNotWhitespace
         >>. skipString "@"
-        >>. many1Chars (satisfy isAsciiLetter <|> satisfy isDigit <|> anyOf "._-")
+        >>. many1Chars (
+            satisfy isAsciiLetterOrNumber
+            <|> attempt (anyOf "._-" .>> nextCharSatisfies isAsciiLetterOrNumber)
+        )
         .>>. opt (skipChar '@' >>. domain)
         .>> (lookAhead
              <| choice

Iceshrimp.Tests/Parsing/MfmTests.cs

@@ -66,10 +66,13 @@ public class MfmTests
 	[TestMethod]
 	public void TestMention()
 	{
-		const string input = "test @test test";
+		const string input = "test @test test @test@instance.tld";
 		List<MfmNode> expected =
 		[
-			new MfmTextNode("test "), new MfmMentionNode("test", "test", null), new MfmTextNode(" test")
+			new MfmTextNode("test "),
+			new MfmMentionNode("test", "test", null),
+			new MfmTextNode(" test "),
+			new MfmMentionNode("test@instance.tld", "test", "instance.tld")
 		];
 		var res = Mfm.parse(input);
 
@@ -90,6 +93,30 @@ public class MfmTests
 		MfmSerializer.Serialize(res).Should().BeEquivalentTo(input);
 	}
 
+	[TestMethod]
+	public void TestMentionTrailingDot()
+	{
+		const string  input    = "@test@asdf.com.";
+		List<MfmNode> expected = [new MfmMentionNode("test@asdf.com", "test", "asdf.com"), new MfmTextNode(".")];
+		var           res      = Mfm.parse(input);
+
+		AssertionOptions.FormattingOptions.MaxDepth = 100;
+		res.ToList().Should().Equal(expected, MfmNodeEqual);
+		MfmSerializer.Serialize(res).Should().BeEquivalentTo(input);
+	}
+
+	[TestMethod]
+	public void TestMentionTrailingDotLocal()
+	{
+		const string  input    = "@test.";
+		List<MfmNode> expected = [new MfmMentionNode("test", "test", null), new MfmTextNode(".")];
+		var           res      = Mfm.parse(input);
+
+		AssertionOptions.FormattingOptions.MaxDepth = 100;
+		res.ToList().Should().Equal(expected, MfmNodeEqual);
+		MfmSerializer.Serialize(res).Should().BeEquivalentTo(input);
+	}
+
 	[TestMethod]
 	public void TestCodeBlock()
 	{