Interface changes after rebase

R/model.R

@@ -25,7 +25,8 @@ mcstate_model_properties <- function(has_gradient = NULL,
                                      has_direct_sample = NULL,
                                      is_stochastic = NULL) {
   ret <- list(has_gradient = has_gradient,
-              has_direct_sample = has_direct_sample)
+              has_direct_sample = has_direct_sample,
+              is_stochastic = is_stochastic)
   class(ret) <- "mcstate_model_properties"
   ret
 }
@@ -247,12 +248,23 @@ validate_model_rng_state <- function(model, properties, call) {
   if (isFALSE(properties$is_stochastic)) {
     return(NULL)
   }
+  if (is.null(properties$is_stochastic) && is.null(model$set_rng_state)) {
+    return(NULL)
+  }
   if (!is.function(model$set_rng_state)) {
+    if (isTRUE(model$is_stochastic)) {
+      hint <- paste("You have specified 'is_stochastic = TRUE', so in order",
+                    "to use your stochastic model we need a way of setting",
+                    "its state")
+    } else {
+      hint <- paste("I found a non-function element 'set_rng_state' within",
+                    "your model and you have not set the 'is_stochastic'",
+                    "property")
+    }
     cli::cli_abort(
       c("Expected 'model$set_rng_state' to be a function",
-        i = paste("You have specified 'is_stochastic = TRUE', so in order",
-                  "to use your stochastic model we need a way of setting",
-                  "its state")))
+        i = hint),
+      arg = "model", call = call)
   }
   list(set = model$set_rng_state)
 }

tests/testthat/helper-mcstate2.R

@@ -73,5 +73,5 @@ ex_dust_sir <- function(n_particles = 100, n_threads = 1,
          parameters = c("beta", "gamma"),
          domain = cbind(c(0, 0), c(Inf, Inf)),
          set_rng_state = set_rng_state),
-    is_stochastic = !deterministic)
+    mcstate_model_properties(is_stochastic = !deterministic))
 }

tests/testthat/test-model.R

@@ -128,4 +128,9 @@ test_that("stochastic models need an rng setting function", {
       mcstate_model_properties(is_stochastic = TRUE)),
     "Expected 'model$set_rng_state' to be a function",
     fixed = TRUE)
+  expect_error(
+    mcstate_model(
+      list(density = identity, parameters = "a", set_rng_state = TRUE)),
+    "Expected 'model$set_rng_state' to be a function",
+    fixed = TRUE)
 })