guard against evaluation of active bindings

[MilesMcBain]

• when inspecting environments
• when composing data view of environments

fixes #1030

What problem did you solve?

Fixed evaluation of active bindings when collecting data for the data view and the workspace viewer.

It may be that the guard is only desired when looking in the global environment for the workspace view?

(If you do not have screenshot) How can I check this pull request?

Check the test code from #1030 and confirm "get" is no longer printed, except when the active binding is accessed:

> f <- local( {
+     x <- 1
+     function(v) {
+        if (missing(v))
+            cat("get\n")
+        else {
+            cat("set\n")
+            x <<- v
+        }
+        x
+     }
+ })
> makeActiveBinding("fred", f, .GlobalEnv)
> bindingIsActive("fred", .GlobalEnv)
[1] TRUE
> fred
get
[1] 1

[renkun-ken]

Just curious, does bindingIsActive evaluate a promise in the first place?

[MilesMcBain]

HA. I'll have to check. That would be fun.

[renkun-ken]

fun <- function(x) {
  bindingIsActive("x", environment())
}

fun(stop("early evaluation!"))

Looks like bindingIsActive is safe.

[renkun-ken]

LGTM Thanks!