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 strong' 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.

Add method `translate_styles` that manually converts the pygments
`bold italic` style into the urwid-compatible `bold, italics`.

Tests added.

Fixes part of zulip#1434.

tests/config/test_themes.py

@@ -12,6 +12,7 @@
 from zulipterminal.config.regexes import REGEX_COLOR_VALID_FORMATS
 from zulipterminal.config.themes import (
     REQUIRED_STYLES,
+    STYLE_TRANSLATIONS,
     THEMES,
     InvalidThemeColorCode,
     MissingThemeAttributeError,
@@ -21,6 +22,7 @@
     generate_pygments_styles,
     generate_theme,
     parse_themefile,
+    translate_styles,
     valid_16_color_codes,
     validate_colors,
 )
@@ -402,3 +404,64 @@ class Color3(Enum):
         + "- GRAY_244 = dark_gra\n"
         + "- LIGHT2 = whit"
     )
+
+
+@pytest.mark.parametrize(
+    "styles, expected_styles, translations",
+    [
+        case(
+            {},
+            {},
+            STYLE_TRANSLATIONS,
+            id="empty_input",
+        ),
+        case(
+            {
+                "token1": "style1",
+                "token2": "style2",
+            },
+            {
+                "token1": "style1",
+                "token2": "style2",
+            },
+            {},
+            id="empty_translations",
+        ),
+        case(
+            {
+                "token1": "bold italic",
+                "token2": "italic bold",
+                "token3": "italic #abc",
+            },
+            {
+                "token1": "bold, italics",
+                "token2": "italics, bold",
+                "token3": "italics, #abc",
+            },
+            STYLE_TRANSLATIONS,
+            id="default_translations",
+        ),
+        case(
+            {
+                "token1": "style italic",
+                "token3": "#abc",
+            },
+            {
+                "token1": "newstyle italic",
+                "token3": "#abc",
+            },
+            {"style": "newstyle"},
+            id="custom_translations",
+        ),
+    ],
+)
+def test_translate_styles(
+    mocker: MockerFixture,
+    styles: Dict[Any, str],
+    expected_styles: Dict[Any, str],
+    translations: Dict[str, str],
+) -> None:
+    pygments_styles = translate_styles(styles, translations)
+
+    for style in expected_styles:
+        assert style in pygments_styles

zulipterminal/config/themes.py

@@ -128,6 +128,12 @@
     "white",
 ]
 
+# These are translations for translating pygments styles into urwid-compatible styles
+STYLE_TRANSLATIONS = {
+    " ": ",",
+    "italic": "italics",
+}
+
 
 class ThemeError(Exception):
     pass
@@ -255,6 +261,28 @@ def parse_themefile(
     return urwid_theme
 
 
+def translate_styles(
+    styles: Dict[Any, str], translations: Dict[str, str] = STYLE_TRANSLATIONS
+) -> Dict[Any, str]:
+    """
+    This function translates pygments styles into urwid compatible styles.
+
+    Parameters:
+    - styles (Dict[Any, str]): pygments styles
+    - translations (Dict[str, str]): replacements to be applied
+
+    Returns:
+    - Dict[Any, str]: translated urwid-compatible styles
+    """
+    translated_styles = {}
+    for token, style in styles.items():
+        updated_style = style
+        for old_value, new_value in translations.items():
+            updated_style = updated_style.replace(old_value, new_value)
+        translated_styles[token] = updated_style
+    return translated_styles
+
+
 def generate_pygments_styles(pygments: Dict[str, Any]) -> ThemeSpec:
     """
     This function adds pygments styles for use in syntax
@@ -278,6 +306,9 @@ def generate_pygments_styles(pygments: Dict[str, Any]) -> ThemeSpec:
     term16_bg = term16.background_color
 
     theme_styles_from_pygments: ThemeSpec = []
+
+    pygments_styles = translate_styles(pygments_styles)
+
     for token, css_class in STANDARD_TYPES.items():
         if css_class in pygments_overrides:
             pygments_styles[token] = pygments_overrides[css_class]