config/themes: Convert pygments styles to urwid compatible styles.

Pygments 2.16.0 introduced a style to support a combination of bold and
italic styling in pygments/pygments#2444. Both of our gruvbox themes and
the light native theme gain a 'bold italic' style via pygments as a
result, which urwid fails to parse and blocks the application from
loading.

This work would represent a clean fix for zulip#1431, which was temporarily
fixed by pinning pygments at ~=2.15.1 in zulip#1433.

This minimally handles spaces and the shortened `italic` in pygments
styles, sufficient to resolve the current style issue. Note that other
pygments styles in themes that we do not yet use may need additional
translation or adjustment.

Tests added.

Fixes part of zulip#1434.

tests/config/test_themes.py

@@ -5,13 +5,14 @@
 import pytest
 from pygments.styles.material import MaterialStyle
 from pygments.styles.perldoc import PerldocStyle
-from pygments.token import STANDARD_TYPES
+from pygments.token import STANDARD_TYPES, _TokenType
 from pytest import param as case
 from pytest_mock import MockerFixture
 
 from zulipterminal.config.regexes import REGEX_COLOR_VALID_FORMATS
 from zulipterminal.config.themes import (
     REQUIRED_STYLES,
+    STYLE_TRANSLATIONS,
     THEMES,
     InvalidThemeColorCode,
     MissingThemeAttributeError,
@@ -20,6 +21,7 @@
     complete_and_incomplete_themes,
     generate_pygments_styles,
     generate_theme,
+    generate_urwid_compatible_pygments_styles,
     parse_themefile,
     valid_16_color_codes,
     validate_colors,
@@ -402,3 +404,65 @@ class Color3(Enum):
         + "- GRAY_244 = dark_gra\n"
         + "- LIGHT2 = whit"
     )
+
+
+@pytest.mark.parametrize(
+    "pygments_styles, expected_styles, style_translations",
+    [
+        case(
+            {},
+            {},
+            STYLE_TRANSLATIONS,
+            id="empty_input",
+        ),
+        case(
+            {
+                "token1": "style1",
+                "token2": "style2",
+            },
+            {
+                "token1": "style1",
+                "token2": "style2",
+            },
+            {},
+            id="empty_translations",
+        ),
+        case(
+            {
+                "token1": "bold italic",  # pygments/pygments#2444
+                "token2": "italic bold",  # + order shouldn't matter
+                "token3": "italic #abc",  # + italic should work with color
+            },
+            {
+                "token1": "bold,italics",
+                "token2": "italics,bold",
+                "token3": "italics,#abc",
+            },
+            STYLE_TRANSLATIONS,
+            id="default_translations",
+        ),
+        case(
+            {
+                "token1": "style italic",
+                "token2": "#abc",
+            },
+            {
+                "token1": "newstyle italic",
+                "token2": "#abc",
+            },
+            {"style": "newstyle"},
+            id="custom_translations",
+        ),
+    ],
+)
+def test_generate_urwid_compatible_pygments_styles(
+    pygments_styles: Dict[_TokenType, str],  # NOTE: placeholder string values used
+    expected_styles: Dict[_TokenType, str],  #       in parametrized dict keys
+    style_translations: Dict[str, str],
+) -> None:
+    generated_styles = generate_urwid_compatible_pygments_styles(
+        pygments_styles, style_translations
+    )
+
+    assert set(expected_styles) == set(generated_styles)  # keys unchanged
+    assert sorted(expected_styles.items()) == sorted(generated_styles.items())

zulipterminal/config/themes.py

@@ -3,7 +3,7 @@
 """
 from typing import Any, Dict, List, Optional, Tuple, Union
 
-from pygments.token import STANDARD_TYPES
+from pygments.token import STANDARD_TYPES, _TokenType
 
 from zulipterminal.config.color import term16
 from zulipterminal.themes import gruvbox_dark, gruvbox_light, zt_blue, zt_dark, zt_light
@@ -128,6 +128,13 @@
     "white",
 ]
 
+# These are style_translations for translating pygments styles into
+# urwid-compatible styles
+STYLE_TRANSLATIONS = {
+    " ": ",",
+    "italic": "italics",
+}
+
 
 class ThemeError(Exception):
     pass
@@ -255,6 +262,19 @@ def parse_themefile(
     return urwid_theme
 
 
+def generate_urwid_compatible_pygments_styles(
+    pygments_styles: Dict[_TokenType, str],
+    style_translations: Dict[str, str] = STYLE_TRANSLATIONS,
+) -> Dict[_TokenType, str]:
+    urwid_compatible_styles = {}
+    for token, style in pygments_styles.items():
+        updated_style = style
+        for old_value, new_value in style_translations.items():
+            updated_style = updated_style.replace(old_value, new_value)
+        urwid_compatible_styles[token] = updated_style
+    return urwid_compatible_styles
+
+
 def generate_pygments_styles(pygments: Dict[str, Any]) -> ThemeSpec:
     """
     This function adds pygments styles for use in syntax
@@ -278,6 +298,8 @@ def generate_pygments_styles(pygments: Dict[str, Any]) -> ThemeSpec:
     term16_bg = term16.background_color
 
     theme_styles_from_pygments: ThemeSpec = []
+    pygments_styles = generate_urwid_compatible_pygments_styles(pygments_styles)
+
     for token, css_class in STANDARD_TYPES.items():
         if css_class in pygments_overrides:
             pygments_styles[token] = pygments_overrides[css_class]