add utility function to calculate underline size for category names

src/towncrier/_builder.py

@@ -7,6 +7,7 @@
 import os
 import re
 import textwrap
+import unicodedata
 
 from collections import defaultdict
 from pathlib import Path
@@ -159,6 +160,22 @@ def find_fragments(
     return content, fragment_files
 
 
+def get_underline_size(text: str) -> int:
+    """
+    Given `text` determine the underline size needed for the reStructuredText output.
+
+    Particularly helps determine if an extra underline is needed for wide characters like emojis.
+    """
+    underline_size: int = 0
+    for char in text:
+        if unicodedata.east_asian_width(char) in ("W", "F"):
+            underline_size += 2
+        else:
+            underline_size += 1
+
+    return underline_size
+
+
 def indent(text: str, prefix: str) -> str:
     """
     Adds `prefix` to the beginning of non-empty lines in `text`.
@@ -202,6 +219,11 @@ def split_fragments(
                 # it's recorded.
                 content = ""
 
+            # Calculate the underline size for the name of the category.
+            definitions[category]["underline_size"] = get_underline_size(
+                definitions[category]["name"]
+            )
+
             texts = section.setdefault(category, {})
 
             issues = texts.setdefault(content, [])

src/towncrier/newsfragments/626.bugfix.rst

@@ -0,0 +1 @@
+Fixed section names not having enough underline characters for emojis.

src/towncrier/templates/default.rst

@@ -16,7 +16,7 @@
 {% if sections[section] %}
 {% for category, val in definitions.items() if category in sections[section]%}
 {{ definitions[category]['name'] }}
-{{ underline * definitions[category]['name']|length }}
+{{ underline * definitions[category]['underline_size'] }}
 
 {% for text, values in sections[section][category].items() %}
 - {% if text %}{{ text }}{% if values %} ({{ values|join(', ') }}){% endif %}{% else %}{{ values|join(', ') }}{% endif  %}

src/towncrier/templates/hr-between-versions.rst

@@ -16,7 +16,7 @@
 {% if sections[section] %}
 {% for category, val in definitions.items() if category in sections[section]%}
 {{ definitions[category]['name'] }}
-{{ underline * definitions[category]['name']|length }}
+{{ underline * definitions[category]['underline_size'] }}
 
 {% if definitions[category]['showcontent'] %}
 {% for text, values in sections[section][category].items() %}

src/towncrier/templates/single-file-no-bullets.rst

@@ -16,7 +16,7 @@
 {% for category, val in definitions.items() if category in sections[section] %}
 
 {{ definitions[category]['name'] }}
-{{ underline * definitions[category]['name']|length }}
+{{ underline * definitions[category]['underline_size'] }}
 
 {% if definitions[category]['showcontent'] %}
 {% for text, values in sections[section][category].items() %}

src/towncrier/test/test_builder.py

@@ -5,7 +5,7 @@
 
 from twisted.trial.unittest import TestCase
 
-from .._builder import parse_newfragment_basename, render_fragments
+from .._builder import get_underline_size, parse_newfragment_basename, render_fragments
 
 
 class TestParseNewsfragmentBasename(TestCase):
@@ -204,3 +204,13 @@ def test_ordering(self):
             - Added Fish
 """
         )
+
+
+class TestUtilityFunctions(TestCase):
+    def test_get_underline_size_ascii(self):
+        """Determine underline size for normal ASCII strings."""
+        assert get_underline_size("bugfixes") == 8
+
+    def test_get_underline_size_wide_character(self):
+        """Determine underline size for strings with wide characters."""
+        assert get_underline_size("🐛 Bugfixes") == 11