Wrapping of user-supplied expressions in renderPlotly

[cpsievert]

Another attempt at #1539, which was merged before fully understanding the shinytest failure (my bad). Note that the merge commit was already reverted on master via 2856731

I had tested #1539 on some minimal apps, but it turns out it would fail on any renderPlotly() statement that contained a reactive read. For example:

library(shiny)
library(plotly)

ui <- fluidPage(
  selectInput("x", "X", names(diamonds)),
  plotlyOutput("p")
)

server <- function(input, output, session) {
  output$p <- renderPlotly({
    plot_ly(x = 1, y = 1, text = input$x)
  })
}
shinyApp(ui, server)

Error in .getReactiveEnvironment()$currentContext: Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
  71: stop
  70: .getReactiveEnvironment()$currentContext [/Users/cpsievert/github/shiny/R/react.R#143]
  69: getCurrentContext [/Users/cpsievert/github/shiny/R/react.R#202]
  65: .subset2(x, "impl")$get [/Users/cpsievert/github/shiny/R/reactives.R#344]
  64: $.reactivevalues [/Users/cpsievert/github/shiny/R/reactives.R#605]
  61: renderPlotly [#4]
  60: func
  53: renderPlotly [/Users/cpsievert/github/plotly/R/shiny.R#52]
  52: server [#3]
Error in .getReactiveEnvironment()$currentContext() : 
  Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

I believe the problem is due to prepareWidget(func()) being evaluated too early? 1a714b8 addresses the problem by passing this in as a quoted expression.