Add clientdata accessor to session; allow access to input names via dir()

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `shiny create` includes new and improved `ui.Chat()` template options. Most of these templates leverage the new [`{chatlas}` package](https://posit-dev.github.io/chatlas/), our opinionated approach to interfacing with various LLM. (#1806)
 
+* Client data values (e.g., url info, output sizes/styles, etc.) can now be accessed in the server-side Python code via `session.clientdata`, which is collection of reactive `Inputs`. For example, `session.clientdata.url_search()` reactively reads the URL search parameters. See [this PR](https://github.com/posit-dev/py-shiny/pull/1832) for a more complete example. (#1832)
+
 ### Bug fixes
 
 * `ui.Chat()` now correctly handles new `ollama.chat()` return value introduced in `ollama` v0.4. (#1787)

shiny/session/_session.py

@@ -170,6 +170,7 @@ class Session(ABC):
     id: str
     input: Inputs
     output: Outputs
+    clientdata: Inputs
     user: str | None
     groups: list[str] | None
 
@@ -519,6 +520,7 @@ def __init__(
 
         self.input: Inputs = Inputs(dict())
         self.output: Outputs = Outputs(self, self.ns, outputs=dict())
+        self.clientdata: Inputs = Inputs(dict())
 
         self.user: str | None = None
         self.groups: list[str] | None = None
@@ -692,7 +694,12 @@ def _manage_inputs(self, data: dict[str, object]) -> None:
             # The keys[0] value is already a fully namespaced id; make that explicit by
             # wrapping it in ResolvedId, otherwise self.input will throw an id
             # validation error.
-            self.input[ResolvedId(keys[0])]._set(val)
+            k = keys[0]
+            self.input[ResolvedId(k)]._set(val)
+
+            if k.startswith(".clientdata_"):
+                k2 = k.split("_", 1)[1]
+                self.clientdata[ResolvedId(k2)]._set(val)
 
         self.output._manage_hidden()
 
@@ -1352,6 +1359,9 @@ def __contains__(self, key: str) -> bool:
         # creates a reactive dependency, and returns whether the value is set.
         return self[key].is_set()
 
+    def __dir__(self):
+        return list(self._map.keys())
+
 
 # ======================================================================================
 # Outputs