Fix #1193: adjust the environment in which R code chunks in Shiny Rmd…

… are evaluated

The environment should not be simply render_args$envir (which defaults to parent.frame() in render()), because Shiny's input/output/session variables are not available in this environment. We have to create a new environment with the environment of Shiny's server function environment being its parent, and render_args$envir being its grandparent environment.

All previous relevant cases #1162, #619, and #1124 have been tested.

Also closes #1194.

R/shiny.R

@@ -225,6 +225,12 @@ rmarkdown_shiny_server <- function(dir, file, encoding, auto_reload, render_args
     else
       function() { file }
 
+    envir_global <- render_args[['envir']]
+    envir_server <- list2env(list(
+      input = input, output = output, session = session
+    ), parent = envir_global)
+    render_args$envir <- new.env(parent = envir_server)
+
     # when the file loads (or is changed), render to a temporary file, and
     # read the contents into a reactive value
     doc <- shiny::reactive({