From aea5efd012dd0cbd06d274ef4fe3993a84d8366f Mon Sep 17 00:00:00 2001
From: Laura Hausmann <laura@hausmann.dev>
Date: Tue, 5 Nov 2024 22:53:57 +0100
Subject: [PATCH] [parsing] Add support for italic and bold segments surrounded
 by underscores (ISH-585)

---
 Iceshrimp.Parsing/Mfm.fs            | 7 ++++++-
 Iceshrimp.Tests/Parsing/MfmTests.cs | 8 ++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/Iceshrimp.Parsing/Mfm.fs b/Iceshrimp.Parsing/Mfm.fs
index 4b326758..378ecea1 100644
--- a/Iceshrimp.Parsing/Mfm.fs
+++ b/Iceshrimp.Parsing/Mfm.fs
@@ -196,7 +196,8 @@ module private MfmParser =
         }
 
     // Patterns
-    let italicPattern = (notFollowedBy <| str "**") >>. skipChar '*'
+    let italicPattern = ((notFollowedBy <| str "**") >>. skipChar '*')
+    let italicPatternAlt = ((notFollowedBy <| str "__") >>. skipChar '_')
     let codePattern = (notFollowedBy <| str "```") >>. skipChar '`'
 
     // Matchers
@@ -207,6 +208,8 @@ module private MfmParser =
 
     let italicNode =
         (italicPattern >>. pushLine >>. manyTill inlineNode italicPattern .>> assertLine)
+        <|> (italicPatternAlt >>. pushLine >>. manyTill inlineNode italicPatternAlt
+             .>> assertLine)
         <|> (skipString "<i>" >>. pushLine >>. manyTill inlineNode (skipString "</i>")
              .>> assertLine)
         |>> fun c -> MfmItalicNode(aggregateTextInline c) :> MfmNode
@@ -214,6 +217,8 @@ module private MfmParser =
     let boldNode =
         (skipString "**" >>. pushLine >>. manyTill inlineNode (skipString "**")
          .>> assertLine)
+        <|> (skipString "__" >>. pushLine >>. manyTill inlineNode (skipString "__")
+             .>> assertLine)
         <|> (skipString "<b>" >>. pushLine >>. manyTill inlineNode (skipString "</b>")
              .>> assertLine)
         |>> fun c -> MfmBoldNode(aggregateTextInline c) :> MfmNode
diff --git a/Iceshrimp.Tests/Parsing/MfmTests.cs b/Iceshrimp.Tests/Parsing/MfmTests.cs
index 7d9e7017..786dc78b 100644
--- a/Iceshrimp.Tests/Parsing/MfmTests.cs
+++ b/Iceshrimp.Tests/Parsing/MfmTests.cs
@@ -24,7 +24,9 @@ public class MfmTests
 		];
 
 		var res         = Mfm.parse("*italic **bold** italic*").ToList();
-		var resAlt      = Mfm.parse("<i>italic <b>bold</b> italic</i>").ToList();
+		var resAlt      = Mfm.parse("_italic **bold** italic_").ToList();
+		var resAlt2     = Mfm.parse("_italic __bold__ italic_").ToList();
+		var resAlt3     = Mfm.parse("<i>italic <b>bold</b> italic</i>").ToList();
 		var resMixed    = Mfm.parse("<i>italic **bold** italic</i>").ToList();
 		var resMixedAlt = Mfm.parse("*italic <b>bold</b> italic*").ToList();
 
@@ -32,6 +34,8 @@ public class MfmTests
 
 		res.Should().Equal(expected, MfmNodeEqual);
 		resAlt.Should().Equal(expected, MfmNodeEqual);
+		resAlt2.Should().Equal(expected, MfmNodeEqual);
+		resAlt3.Should().Equal(expected, MfmNodeEqual);
 		resMixed.Should().Equal(expected, MfmNodeEqual);
 		resMixedAlt.Should().Equal(expected, MfmNodeEqual);
 	}
@@ -380,7 +384,7 @@ public class MfmTests
 		{
 			var pre = Stopwatch.GetTimestamp();
 			Mfm.parse(mfm);
-			var ms   = Stopwatch.GetElapsedTime(pre).GetTotalMilliseconds();
+			var ms = Stopwatch.GetElapsedTime(pre).GetTotalMilliseconds();
 			Console.WriteLine($@"Took {ms} ms");
 			return ms;
 		}