save_metric_files: fix doc and error message, and add tests

R/fit.R

@@ -916,7 +916,8 @@ CmdStanFit$set("public", name = "cmdstan_diagnose", value = cmdstan_diagnose)
 #'
 #' For `$save_metric_files()` everything is the same as for
 #' `$save_output_files()` except `"-metric-"` is included in the new
-#' file name after `basename`.
+#' file name after `basename`. Make sure to set `save_metric=TRUE` when
+#' fitting the model.
 #'
 #' For `$save_config_files()` everything is the same as for
 #' `$save_output_files()` except `"-config-"` is included in the new

R/run.R

@@ -258,6 +258,12 @@ CmdStanRun <- R6::R6Class(
                                  timestamp = TRUE,
                                  random = TRUE) {
       current_files <- self$metric_files(include_failed = TRUE) # used so we get error if 0 files
+      if (is.null(current_files)) {
+        stop(
+          "No metric files found. Make sure to set 'save_metric=TRUE' when fitting the model.",
+          call. = FALSE
+        )
+      }
       new_paths <- copy_temp_files(
         current_paths = current_files,
         new_dir = dir,

man-roxygen/model-sample-args.R

@@ -94,5 +94,5 @@
 #' @param save_metric (logical) When `TRUE`, call CmdStan with argument
 #'   `"adaptation save_metric=1"` to save the adapted metric in separate JSON
 #'   file with elements "stepsize", "metric_type" and "inv_metric". The default
-#'   is `TRUE`. This option is only available in CmdStan 2.34.0 and later.
+#'    is `FALSE`. This option is only available in CmdStan 2.34.0 and later.
 #'

tests/testthat/test-fit-mcmc.R

@@ -399,3 +399,14 @@ test_that("metadata()$time has chains rowss", {
   expect_equal(nrow(fit_mcmc_2$metadata()$time), fit_mcmc_2$num_chains())
   expect_equal(nrow(fit_mcmc_3$metadata()$time), fit_mcmc_3$num_chains())
 })
+
+test_that("save_metric_files works and has clear error message when no files", {
+  expect_error(
+    fit_mcmc$save_metric_files(),
+    "No metric files found"
+  )
+  fit_save_metric <- testing_fit("logistic", save_metric = TRUE)
+  paths <- fit_save_metric$save_metric_files()
+  checkmate::expect_file_exists(paths, extension = "json")
+  expect_true(all(file.size(paths) > 0))
+})