From c190c5d473c976f0d4726ca5f42a262903f42f52 Mon Sep 17 00:00:00 2001
From: Andrew Johnson <andrew.johnson@arjohnsonau.com>
Date: Mon, 25 Sep 2023 12:01:52 +0300
Subject: [PATCH 1/2] Fix handling of single-length inits for containers

---
 R/args.R                         |  7 +++++++
 tests/testthat/test-model-init.R | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/R/args.R b/R/args.R
index 7794510e4..56d08611b 100644
--- a/R/args.R
+++ b/R/args.R
@@ -826,6 +826,13 @@ process_init_list <- function(init, num_procs, model_variables = NULL) {
       if (!all(is_parameter_value_supplied)) {
         missing_parameter_values[[i]] <- parameter_names[!is_parameter_value_supplied]
       }
+      for (par_name in parameter_names[is_parameter_value_supplied]) {
+        # Make sure that initial values for single-element containers don't get
+        # unboxed when writing to JSON
+        if (model_variables$parameters[[par_name]]$dimensions == 1 && is.null(attr(init[[i]][[par_name]], "dim"))) {
+          init[[i]][[par_name]] <- array(init[[i]][[par_name]], dim = 1)
+        }
+      }
     }
     if (length(missing_parameter_values) > 0) {
       warning_message <- c(
diff --git a/tests/testthat/test-model-init.R b/tests/testthat/test-model-init.R
index 221c8dfb3..cbf66c264 100644
--- a/tests/testthat/test-model-init.R
+++ b/tests/testthat/test-model-init.R
@@ -262,3 +262,25 @@ test_that("print message if not all parameters are initialized", {
     fixed = TRUE
   )
 })
+
+test_that("Initial values for single-element containers treated correctly", {
+  modcode <- "
+  data {
+    real y_mean;
+  }
+  parameters {
+    vector[1] y;
+  }
+  model {
+    y_mean ~ normal(y[1], 1);
+  }
+  "
+  mod <- cmdstan_model(write_stan_file(modcode), force_recompile = TRUE)
+  expect_no_error(
+    fit <- mod$sample(
+      data = list(y_mean = 0),
+      init = list(list(y = c(0))),
+      chains = 1
+    )
+  )
+})

From 50616d0d070913c2112ac12b5b3f2a312f41107e Mon Sep 17 00:00:00 2001
From: Andrew Johnson <andrew.johnson@arjohnsonau.com>
Date: Mon, 25 Sep 2023 18:37:54 +0300
Subject: [PATCH 2/2] Fix dim check

---
 R/args.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R/args.R b/R/args.R
index 56d08611b..a2a31af08 100644
--- a/R/args.R
+++ b/R/args.R
@@ -829,7 +829,7 @@ process_init_list <- function(init, num_procs, model_variables = NULL) {
       for (par_name in parameter_names[is_parameter_value_supplied]) {
         # Make sure that initial values for single-element containers don't get
         # unboxed when writing to JSON
-        if (model_variables$parameters[[par_name]]$dimensions == 1 && is.null(attr(init[[i]][[par_name]], "dim"))) {
+        if (model_variables$parameters[[par_name]]$dimensions == 1 && length(init[[i]][[par_name]]) == 1) {
           init[[i]][[par_name]] <- array(init[[i]][[par_name]], dim = 1)
         }
       }