From 624db9a0b0c1b12cfb5b6df01f1def7a0d284d93 Mon Sep 17 00:00:00 2001
From: Stanislav <vissi@vissi.su>
Date: Fri, 16 Oct 2026 02:48:25 +0400
Subject: [PATCH] Raise unknown named character errors with the sntufn tag

parse_escape_sequence raised NamedCharacterSyntaxError("Syntax", "sntufn", ...),
but SyntaxError takes the message tag as its first argument (the name is
always "Syntax"). The message then came out as
"Syntax::Syntax: Message Syntax::Syntax not found" instead of
"Syntax::sntufn: Unknown unicode longname ...".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 mathics_scanner/escape_sequences.py |  4 ++--
 test/test_escape_sequences.py       | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/mathics_scanner/escape_sequences.py b/mathics_scanner/escape_sequences.py
index b0675b92..ef9b3e17 100644
--- a/mathics_scanner/escape_sequences.py
+++ b/mathics_scanner/escape_sequences.py
@@ -117,11 +117,11 @@ def parse_escape_sequence(
         if i == len(source_text):
             # Note: named characters do not have \n's in them. (Is this right)?
             # FIXME: decide what to do here.
-            raise NamedCharacterSyntaxError("Syntax", "sntufn", source_text[pos:])
+            raise NamedCharacterSyntaxError("sntufn", source_text[pos:])
 
         named_character = parse_named_character(source_text, pos, i)
         if named_character is None:
-            raise NamedCharacterSyntaxError("Syntax", "sntufn", source_text[pos:i])
+            raise NamedCharacterSyntaxError("sntufn", source_text[pos:i])
 
         result += named_character
         pos = i + 1
diff --git a/test/test_escape_sequences.py b/test/test_escape_sequences.py
index f9631089..4b912e47 100644
--- a/test/test_escape_sequences.py
+++ b/test/test_escape_sequences.py
@@ -57,6 +57,26 @@ def test_invalid_named_character_sequences():
             parse_escape_sequence(text, 1, is_in_string=False)
 
 
+@pytest.mark.parametrize(
+    ("text", "name"),
+    [
+        (r"\[Fake]", "Fake"),
+        (r"\[Alpha\]", "Alpha\\"),
+        (r"\[\Sigma]", "\\Sigma"),
+        (r"\[Theta", "Theta"),
+    ],
+)
+def test_invalid_named_character_message(text, name):
+    """The error carries the "sntufn" tag and the unknown name as its first argument,
+    which is what the Syntax::sntufn message template expects."""
+    with pytest.raises(NamedCharacterSyntaxError) as excinfo:
+        parse_escape_sequence(text, 1, is_in_string=False)
+    error = excinfo.value
+    assert error.name == "Syntax"
+    assert error.tag == "sntufn"
+    assert error.args[0] == name
+
+
 def test_invalid_number_encoding():
     for text in (
         # Octal