gnoweb: an unticked checkbox in a gno-form submits its value

[aditya-manit]

Description

In a gno-form with an exec function, a checkbox the user never ticks still contributes
its value to the transaction. A boolean-ish parameter is therefore always "on", and there
is no way to submit "off" from the browser. Every other input type in the same form behaves
correctly.

Because a Gno function cannot accept "" for a bool (unexpected bool value ""), such
parameters tend to be declared as strings — so this fails silently rather than loudly.

Your environment

• gnoweb as served at pearl.testnets.gno.land
• Gno commit: c4c72fdd288c757e8da0d93aae867fa479b1b15c (tag chain/pearl); the JS quoted
  below is unchanged on master
• Desktop browser with the Adena extension

Steps to reproduce

1. Deploy a realm whose Render emits a form with p/jeronimoalbi/mdform:

   form := mdform.New("exec", "Submit")
   form.Input("name", "placeholder", "Name")
   form.Checkbox("required", "1", "description", "Required?")
   res.Write(form.String())

2. Open the page, fill in name, leave the checkbox untouched, submit.

3. Inspect the transaction the wallet is handed.

A form already deployed for this is at
https://pearl.testnets.gno.land/r/nym-encapsulate001/test2, whose index renders eight
rows of label / kind / required / options.

Expected behaviour

An unticked checkbox contributes no value, as an unticked checkbox does in an ordinary HTML
form.

Actual behaviour

It contributes its value attribute, indistinguishable from having been ticked.

Logs

Transaction 5bca8a623d4d47146d2c3def47e05b3a86d538306a192f56622cab9a4e7cb657 (pearl-1,
height 269777). Five rows were filled in; rows 6-8 were left completely untouched. Decoded
arguments for those rows:

arg	control	submitted	expected
l6, l7, l8	text input	""	"" ✓
k6, k7, k8	select, default text	"text"	"text" ✓
o6, o7, o8	text input	""	"" ✓
r6, r7, r8	checkbox, value="1"	"1"	"" ✗
deadline	number input	""	"" ✓

Untouched selects sent their default and untouched text/number inputs sent empty, so the
behaviour is specific to checkboxes.

It is not the realm's markdown, which emits no checked:

<gno-input type="checkbox" name="r6" value="1" description="Field 6 required" />

and not the rendered HTML, which is also unchecked — the full served tag:

<input type="checkbox" id="r6_43" name="r6" value="1" aria-labelledby="desc_r6_43"
       data-action-function-target="param-input"
       data-action="change->action-function#updateAllArgs"
       data-action-function-param-value="r6" />

There is no checked anywhere on the page, so the value appears during argument collection
rather than at render time.

Proposed solution

I traced this partway and stopped short of confirming it, so treat the mechanism as a
hypothesis and the behaviour above as the finding.

In gno.land/pkg/gnoweb/frontend/js/controller-action-function.ts,
_getParamCurrentValue does filter checkboxes by .checked, but _initializeArgs only
pushes a value when it is truthy (line 127 on master):

const paramValue = this._getParamCurrentValue(paramName);
this._params[paramName] = paramValue;
if (paramValue) this._updateArgInDOM(paramName, paramValue);

An unchecked box therefore never writes its empty value into the arg nodes or the execute
URL. What then supplies "1" is where I stopped — I did not find where those are first
populated. If that is the cause, initialising every param unconditionally (writing the
empty string rather than skipping it) would fix it.

Workaround for realm authors meanwhile: use a two-option <select> (no / yes).
Untouched selects submit their selected option correctly — verified at
https://pearl.testnets.gno.land/r/nym-encapsulate001/test3.