action_age: Explicit error if age dimension missing #134

Without an age dimension, the stock_ss() calls will fail, but it's not
a sensible thing to do in the first place.

Fail with an informative error message.

R/action_age.R

@@ -6,6 +6,8 @@ g3a_age <- function(
         run_f = ~cur_step_final,
         run_at = g3_action_order$age,
         transition_at = g3_action_order$age ) {
+    if (is.null(tryCatch(g3_stock_def(stock, 'minage'), error = function(x) NULL))) stop("stock missing age ", stock$name)
+
     out <- new.env(parent = emptyenv())
 
     stock__num <- g3_stock_instance(stock, 0)

tests/test-action_age.R

@@ -3,6 +3,12 @@ library(unittest)
 
 library(gadget3)
 
+ok_group("g3a_age:no_age")
+ok(ut_cmp_error({
+    g3a_age(g3_stock('prey_a', seq(20, 40, 4)))
+}, "age.*prey_a"), "Cannot use g3a_age() without an age dimension")
+#### g3a_age:no_age
+
 ok_group("g3a_age:single_age", {
     # prey_a, with single age, outputs into b & c
     prey_a <- g3_stock('prey_a', seq(20, 40, 4)) %>% g3s_age(11, 11)