Ensure that callbacks fire in a FIFO order

Version bump required so Leaflet can detect this fix

R/map.R

@@ -23,6 +23,9 @@ Map <- R6Class(
       env[[key]] <- value
       value
     },
+    mget = function(keys) {
+      base::mget(keys, env)
+    },
     mset = function(...) {
       args <- list(...)
       if (length(args) == 0)

R/utils.R

@@ -580,7 +580,11 @@ Callbacks <- R6Class(
       })
     },
     invoke = function(..., onError=NULL) {
-      for (callback in .callbacks$values()) {
+      # Ensure that calls are invoked in the order that they were registered
+      keys <- as.character(sort(as.integer(.callbacks$keys()), decreasing = TRUE))
+      callbacks <- .callbacks$mget(keys)
+
+      for (callback in callbacks) {
         if (is.null(onError)) {
           callback(...)
         } else {

inst/tests/test-utils.R

@@ -100,3 +100,20 @@ test_that("anyUnnamed works as expected", {
   x <- x[3:4]
   expect_true(anyUnnamed(x))
 })
+
+test_that("Callbacks fire in predictable order", {
+  cb <- Callbacks$new()
+
+  x <- numeric(0)
+  cb$register(function() {
+    x <<- c(x, 1)
+  })
+  cb$register(function() {
+    x <<- c(x, 2)
+  })
+  cb$register(function() {
+    x <<- c(x, 3)
+  })
+  cb$invoke()
+  expect_equal(x, c(1, 2, 3))
+})