fix: Use posix paths in import statements in Sass strings (#1684)

Author: gadenbuie

CHANGELOG.md

@@ -28,7 +28,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   * Fixed a bug with `Chat()` sometimes not removing it's loading icon (on error or a `None` transform). (#1679)
   * `.messages(format="anthropic")` correctly removes non-user starting messages (once again). (#1685)
 
-* `shiny create` now uses the template `id` rather than the directory name as the default directory. (#1666)
+* `shiny create` now uses the template `id` rather than the directory name as the default directory.
+(#1666)
+
+* `ui.Theme()` now works correctly on Windows when the theme requires Sass compilation. (thanks @yuuuxt, #1684)
 
 ## [1.1.0] - 2024-09-03
 

shiny/ui/_theme.py

@@ -510,7 +510,10 @@ def path_pkg_preset(preset: ShinyThemePreset, *args: str) -> str:
     #> "{shiny}/www/shared/sass/preset/shiny/bootstrap.min.css"
     ```
     """
-    return os.path.realpath(path_pkg_www("sass", "preset", str(preset), *args))
+    path = os.path.realpath(path_pkg_www("sass", "preset", str(preset), *args))
+    # these paths end up in strings passed to sass.compile(). Converting to POSIX means
+    # we use forward slashes to avoid needing to double-escape the Windows backslash
+    return pathlib.Path(path).as_posix()
 
 
 def check_is_valid_preset(preset: ShinyThemePreset) -> None: