reactable() doesn't respect `htmlwidget::sizingPolicy()`'s `viewer.fill` (or `browser.fill`)

[cpsievert]

The reason why reactable() currently doesn't fill the RStudio IDE viewer pane (which is the default {htmlwidgets} behavior) is that reactable() passes a default value of "auto" to createWidget()'s height/width

reactable/R/reactable.R

Lines 220 to 221 in f6a4e0a

	width = "auto",
	height = "auto",

reactable/R/reactable.R

Lines 718 to 724 in f6a4e0a

	htmlwidgets::createWidget(
	name = "reactable",
	reactR::reactMarkup(component),
	width = width,
	height = height,
	# Don't limit width when rendered inside an R Notebook
	sizingPolicy = htmlwidgets::sizingPolicy(knitr.figure = FALSE),

This is because htmlwidgets::createWidget() assumes non-NULL values are user specified values. This isn't very well documented, but you can see evidence of this in http://www.htmlwidgets.org/develop_intro.html as well as the code {htmlwidgets} uses to resolve sizingPolicy():

https://github.com/ramnathv/htmlwidgets/blob/cb052ac613ffe13bd6a3f4b6e9333002e72b59d8/R/sizing.R#L193-L194

I've also noticed that we can't simply change width/height's default in reactable to NULL, because of this:

reactable/R/reactable.R

Lines 710 to 716 in f6a4e0a

	if (static) {
	# HACK: widget_html is the only way to customize the widget HTML, but it
	# doesn't have access to the widget attributes. To work around this, we attach
	# the widget attributes as an attribute on width, which just happens to be passed
	# as-is for static rendered HTML widgets.
	attr(width, "ssrGetAttribs") <- function() component$attribs
	}

However, I think I have an idea for removing that "hack", which will allow for non-NULL width.

(P.S., I ran across this because we're currently working on a new fill setting in htmlwidgets::sizingPolicy() that allows widgets to fill a container marked with htmltools::bindFillRole(container = TRUE), which will power "resizable cards" https://rstudio.github.io/bslib/articles/cards.html#responsive-sizing )