Use magic comment

Author: wch

shiny/express/__init__.py

@@ -37,16 +37,6 @@
 session: _Session
 
 
-allow_express_in_core = False
-"""
-Control whether Shiny Express imports are allowed in Shiny Core apps.
-
-Normally Shiny Express imports are not allowed in Shiny Core apps because the mixing of
-the two could lead to confusion. However, there are special cases where we do allow
-this, like when using Shiny Express syntax in a Quarto Dashboard.
-"""
-
-
 # Note that users should use `from shiny.express import input` instead of `from shiny
 # import express` and acces via `express.input`. The former provides a static value for
 # `input`, but the latter is dynamic -- every time `express.input` is accessed, it

shiny/express/_is_express.py

@@ -44,24 +44,29 @@ def is_express_app(app: str, app_dir: str | None) -> bool:
         # Read the file, parse it, and look for any imports of shiny.express.
         with open(app_path) as f:
             content = f.read()
+
+        # Check for magic comment in the first 1000 characters
+        for line in content[:1000].splitlines():
+            line = line.rstrip()
+            if line == "# shiny_mode: express":
+                return True
+            elif line == "# shiny_mode: core":
+                return False
+
         tree = ast.parse(content, app_path)
         detector = DetectShinyExpressVisitor()
         detector.visit(tree)
 
     except Exception:
         return False
 
-    return detector.is_express_app()
+    return detector.found_shiny_express_import
 
 
 class DetectShinyExpressVisitor(ast.NodeVisitor):
     def __init__(self):
         super().__init__()
         self.found_shiny_express_import = False
-        self.found_shiny_express_in_core = False
-
-    def is_express_app(self) -> bool:
-        return self.found_shiny_express_import and not self.found_shiny_express_in_core
 
     def visit_Import(self, node: ast.Import) -> None:
         if any(alias.name == "shiny.express" for alias in node.names):
@@ -75,20 +80,6 @@ def visit_ImportFrom(self, node: ast.ImportFrom) -> None:
         ):
             self.found_shiny_express_import = True
 
-    def visit_Assign(self, node: ast.Assign) -> None:
-        for target in node.targets:
-            # Look for the statement `shiny.express.allow_express_in_core = True` at the
-            # top level.
-            if (
-                isinstance(target, ast.Attribute)
-                and isinstance(target.value, ast.Attribute)
-                and target.value.attr == "express"
-                and isinstance(target.value.value, ast.Name)
-                and target.value.value.id == "shiny"
-                and target.attr == "allow_express_in_core"
-            ):
-                self.found_shiny_express_in_core = True
-
     # Visit top-level nodes.
     def visit_Module(self, node: ast.Module) -> None:
         super().generic_visit(node)

shiny/express/_run.py

@@ -144,15 +144,8 @@ def set_result(x: object):
         get_top_level_recall_context_manager().__exit__(None, None, None)
 
         # If we're running as an Express app but there's also a top-level item named app
-        # which is a shiny.App object, the user probably made a mistake. The exception
-        # is if allow_express_in_core is True, which happens with Quarto Dashboards.
-        from . import allow_express_in_core
-
-        if (
-            not allow_express_in_core
-            and "app" in var_context
-            and isinstance(var_context["app"], App)
-        ):
+        # which is a shiny.App object, the user probably made a mistake.
+        if "app" in var_context and isinstance(var_context["app"], App):
             raise RuntimeError(
                 "This looks like a Shiny Express app because it imports shiny.express, "
                 "but it also looks like a Shiny Core app because it has a variable named "

shiny/quarto.py

@@ -68,14 +68,12 @@ def convert_code_cells_to_app_py(json_file: str | Path, app_file: str | Path) ->
             )
 
     app_content = f"""# This file generated by Quarto; do not edit by hand.
+# shiny_mode: core
 
 from __future__ import annotations
 
 from pathlib import Path
 from shiny import App, Inputs, Outputs, Session, ui
-import shiny.express
-
-shiny.express.allow_express_in_core = True
 
 {"".join(global_code_cell_texts)}