[Bug]: Trivial dependency cycles are not detected, neither output nor errors produced

[pfalcon]

Component

Reactive Programming

Severity

P1 - High (major feature broken)

Shiny Version

1.4.0

Python Version

3.10.12

Minimal Reproducible Example

from shiny.express import input, render, ui


@render.express
def myrender():
    ui.input_select("sel", None, ["All", "So", "Much"], selected="All")
    input.sel()
    "Sadly, we never get here - silently. Poor user will never know why."
    "Actually, nothing is rendered at all."

Behavior

The code above produces no rendered output and no error messages. This can hardly be called "transparent reactivity" (re: https://shiny.posit.co/py/docs/overview.html#reactivity ), as nothing there is transparent.

Expected behavior:
Complexity of dealing with circular dependencies (detecting, and whenever possible, avoiding in a manner of least user surprise) is understood. Yet, apparently, would be nice to do something about such cases.

Error Messages (if any)

None!

Environment

Ubuntu
Chromium 126

[pfalcon]

This leads to 2 arguably obvious questions:

1. Why reactive Value .get() methods doesn't have default param? That would allow to do input.sel.get("All") (ditto for selected=) and bootstrap it.
2. Yet better (from end user perspective, though I imagine pundits would find that controversial), why input_select("sel", ..., selected="All") doesn't pre-populate input.sel with "All" value? That would be truly transparent solution.

[pfalcon]

Why reactive Value .get() methods doesn't have default param?

#2010