From 265c5abe526f10aff8d6a96d79b41dc4e8f93f20 Mon Sep 17 00:00:00 2001
From: Brian Ward <bward@flatironinstitute.org>
Date: Mon, 25 Nov 2024 11:11:14 -0500
Subject: [PATCH] stan_csv_reader: fix trying to read non-existant metric for
 size-0 HMC

---
 src/stan/io/stan_csv_reader.hpp               |   4 +
 src/test/unit/io/stan_csv_reader_test.cpp     |  13 ++
 .../io/test_csv_files/no_parameters_hmc.csv   | 157 ++++++++++++++++++
 3 files changed, 174 insertions(+)
 create mode 100644 src/test/unit/io/test_csv_files/no_parameters_hmc.csv

diff --git a/src/stan/io/stan_csv_reader.hpp b/src/stan/io/stan_csv_reader.hpp
index 22a11947a4..0ca732e32b 100644
--- a/src/stan/io/stan_csv_reader.hpp
+++ b/src/stan/io/stan_csv_reader.hpp
@@ -250,6 +250,10 @@ class stan_csv_reader {
 
     int rows = lines - 3;
     int cols = std::count(line.begin(), line.end(), ',') + 1;
+    if (cols == 1) {
+      // model has no parameters
+      return;
+    }
     adaptation.metric.resize(rows, cols);
     char comment;  // Buffer for comment indicator, #
 
diff --git a/src/test/unit/io/stan_csv_reader_test.cpp b/src/test/unit/io/stan_csv_reader_test.cpp
index 864bd1512e..9a84ce8ccd 100644
--- a/src/test/unit/io/stan_csv_reader_test.cpp
+++ b/src/test/unit/io/stan_csv_reader_test.cpp
@@ -30,6 +30,8 @@ class StanIoStanCsvReader : public testing::Test {
         "src/test/unit/io/test_csv_files/bernoulli_warmup.csv");
     fixed_param_stream.open(
         "src/test/unit/io/test_csv_files/fixed_param_output.csv");
+    no_params_stream.open(
+        "src/test/unit/io/test_csv_files/no_parameters_hmc.csv");
   }
 
   void TearDown() {
@@ -46,6 +48,7 @@ class StanIoStanCsvReader : public testing::Test {
     bernoulli_thin_stream.close();
     bernoulli_warmup_stream.close();
     fixed_param_stream.close();
+    no_params_stream.close();
   }
 
   std::ifstream blocker0_stream, epil0_stream;
@@ -58,6 +61,7 @@ class StanIoStanCsvReader : public testing::Test {
   std::ifstream bernoulli_thin_stream;
   std::ifstream bernoulli_warmup_stream;
   std::ifstream fixed_param_stream;
+  std::ifstream no_params_stream;
 };
 
 TEST_F(StanIoStanCsvReader, read_metadata1) {
@@ -570,6 +574,14 @@ TEST_F(StanIoStanCsvReader, fixed_param) {
   ASSERT_EQ(10, fixed_param.samples.rows());
 }
 
+TEST_F(StanIoStanCsvReader, no_parameters) {
+  stan::io::stan_csv no_parameters_hmc;
+  std::stringstream out;
+  no_parameters_hmc = stan::io::stan_csv_reader::parse(no_params_stream, &out);
+  ASSERT_EQ(100, no_parameters_hmc.samples.rows());
+  ASSERT_EQ(0, no_parameters_hmc.adaptation.metric.size());
+}
+
 TEST_F(StanIoStanCsvReader, no_samples) {
   std::ifstream no_samples_stream;
   no_samples_stream.open(
@@ -590,4 +602,5 @@ TEST_F(StanIoStanCsvReader, variational) {
       = stan::io::stan_csv_reader::parse(variational_stream, &out);
   variational_stream.close();
   ASSERT_EQ(1000, variational.metadata.num_samples);
+  ASSERT_EQ(0, variational.adaptation.metric.size());
 }
diff --git a/src/test/unit/io/test_csv_files/no_parameters_hmc.csv b/src/test/unit/io/test_csv_files/no_parameters_hmc.csv
new file mode 100644
index 0000000000..35dc61f1ac
--- /dev/null
+++ b/src/test/unit/io/test_csv_files/no_parameters_hmc.csv
@@ -0,0 +1,157 @@
+# stan_version_major = 2
+# stan_version_minor = 35
+# stan_version_patch = 0
+# model = sim_model
+# start_datetime = 2024-11-25 16:05:51 UTC
+# method = sample (Default)
+#   sample
+#     num_samples = 100
+#     num_warmup = 100
+#     save_warmup = false (Default)
+#     thin = 1 (Default)
+#     adapt
+#       engaged = true (Default)
+#       gamma = 0.05 (Default)
+#       delta = 0.8 (Default)
+#       kappa = 0.75 (Default)
+#       t0 = 10 (Default)
+#       init_buffer = 75 (Default)
+#       term_buffer = 50 (Default)
+#       window = 25 (Default)
+#       save_metric = false (Default)
+#     algorithm = hmc (Default)
+#       hmc
+#         engine = nuts (Default)
+#           nuts
+#             max_depth = 10 (Default)
+#         metric = diag_e (Default)
+#         metric_file =  (Default)
+#         stepsize = 1 (Default)
+#         stepsize_jitter = 0 (Default)
+#     num_chains = 1 (Default)
+# id = 1 (Default)
+# data
+#   file =  (Default)
+# init = 2 (Default)
+# random
+#   seed = 1799096017 (Default)
+# output
+#   file = output.csv (Default)
+#   diagnostic_file =  (Default)
+#   refresh = 100 (Default)
+#   sig_figs = -1 (Default)
+#   profile_file = profile.csv (Default)
+#   save_cmdstan_config = false (Default)
+# num_threads = 1 (Default)
+# stanc_version = %%NAME%%3 %%VERSION%%
+# stancflags = 
+lp__,accept_stat__,stepsize__,treedepth__,n_leapfrog__,divergent__,energy__,x
+# Adaptation terminated
+# Step size = 1.35996e+14
+# Diagonal elements of inverse mass matrix:
+# 
+0,1,1.35996e+14,1,1,0,0,8.57152
+0,1,1.35996e+14,1,1,0,0,-4.56101
+0,1,1.35996e+14,1,1,0,0,9.30019
+0,1,1.35996e+14,1,1,0,0,-14.6254
+0,1,1.35996e+14,1,1,0,0,8.30123
+0,1,1.35996e+14,1,1,0,0,19.2067
+0,1,1.35996e+14,1,1,0,0,12.6027
+0,1,1.35996e+14,1,1,0,0,-5.70173
+0,1,1.35996e+14,1,1,0,0,3.04002
+0,1,1.35996e+14,1,1,0,0,-8.28215
+0,1,1.35996e+14,1,1,0,0,3.20386
+0,1,1.35996e+14,1,1,0,0,-6.45707
+0,1,1.35996e+14,1,1,0,0,-5.29269
+0,1,1.35996e+14,1,1,0,0,5.1527
+0,1,1.35996e+14,1,1,0,0,-3.69775
+0,1,1.35996e+14,1,1,0,0,-1.77925
+0,1,1.35996e+14,1,1,0,0,-13.7562
+0,1,1.35996e+14,1,1,0,0,-0.789554
+0,1,1.35996e+14,1,1,0,0,-14.0911
+0,1,1.35996e+14,1,1,0,0,-4.71911
+0,1,1.35996e+14,1,1,0,0,-12.7874
+0,1,1.35996e+14,1,1,0,0,15.029
+0,1,1.35996e+14,1,1,0,0,-6.30709
+0,1,1.35996e+14,1,1,0,0,3.50805
+0,1,1.35996e+14,1,1,0,0,9.01495
+0,1,1.35996e+14,1,1,0,0,5.9809
+0,1,1.35996e+14,1,1,0,0,11.02
+0,1,1.35996e+14,1,1,0,0,9.68621
+0,1,1.35996e+14,1,1,0,0,-4.20659
+0,1,1.35996e+14,1,1,0,0,-7.71128
+0,1,1.35996e+14,1,1,0,0,-13.6125
+0,1,1.35996e+14,1,1,0,0,0.541567
+0,1,1.35996e+14,1,1,0,0,-6.96969
+0,1,1.35996e+14,1,1,0,0,2.49902
+0,1,1.35996e+14,1,1,0,0,8.31074
+0,1,1.35996e+14,1,1,0,0,13.4856
+0,1,1.35996e+14,1,1,0,0,-4.60591
+0,1,1.35996e+14,1,1,0,0,6.84733
+0,1,1.35996e+14,1,1,0,0,-16.8676
+0,1,1.35996e+14,1,1,0,0,4.43181
+0,1,1.35996e+14,1,1,0,0,-10.6785
+0,1,1.35996e+14,1,1,0,0,-5.56113
+0,1,1.35996e+14,1,1,0,0,-0.95401
+0,1,1.35996e+14,1,1,0,0,11.2198
+0,1,1.35996e+14,1,1,0,0,3.43417
+0,1,1.35996e+14,1,1,0,0,-11.2942
+0,1,1.35996e+14,1,1,0,0,-14.3029
+0,1,1.35996e+14,1,1,0,0,3.69492
+0,1,1.35996e+14,1,1,0,0,0.319324
+0,1,1.35996e+14,1,1,0,0,-5.95097
+0,1,1.35996e+14,1,1,0,0,5.99333
+0,1,1.35996e+14,1,1,0,0,-6.59629
+0,1,1.35996e+14,1,1,0,0,14.1795
+0,1,1.35996e+14,1,1,0,0,-7.58818
+0,1,1.35996e+14,1,1,0,0,4.89377
+0,1,1.35996e+14,1,1,0,0,4.63195
+0,1,1.35996e+14,1,1,0,0,-4.62905
+0,1,1.35996e+14,1,1,0,0,-11.4145
+0,1,1.35996e+14,1,1,0,0,4.03017
+0,1,1.35996e+14,1,1,0,0,-10.0459
+0,1,1.35996e+14,1,1,0,0,-11.8674
+0,1,1.35996e+14,1,1,0,0,-0.161997
+0,1,1.35996e+14,1,1,0,0,-5.75037
+0,1,1.35996e+14,1,1,0,0,-13.3027
+0,1,1.35996e+14,1,1,0,0,4.86817
+0,1,1.35996e+14,1,1,0,0,11.1937
+0,1,1.35996e+14,1,1,0,0,13.918
+0,1,1.35996e+14,1,1,0,0,-12.2423
+0,1,1.35996e+14,1,1,0,0,22.3588
+0,1,1.35996e+14,1,1,0,0,-8.30628
+0,1,1.35996e+14,1,1,0,0,-6.87127
+0,1,1.35996e+14,1,1,0,0,12.721
+0,1,1.35996e+14,1,1,0,0,-7.86135
+0,1,1.35996e+14,1,1,0,0,-8.56196
+0,1,1.35996e+14,1,1,0,0,-4.04709
+0,1,1.35996e+14,1,1,0,0,-21.6766
+0,1,1.35996e+14,1,1,0,0,-19.6485
+0,1,1.35996e+14,1,1,0,0,1.99421
+0,1,1.35996e+14,1,1,0,0,11.2645
+0,1,1.35996e+14,1,1,0,0,-9.35154
+0,1,1.35996e+14,1,1,0,0,-3.37081
+0,1,1.35996e+14,1,1,0,0,2.46874
+0,1,1.35996e+14,1,1,0,0,7.28248
+0,1,1.35996e+14,1,1,0,0,19.3846
+0,1,1.35996e+14,1,1,0,0,-4.92502
+0,1,1.35996e+14,1,1,0,0,-11.4687
+0,1,1.35996e+14,1,1,0,0,3.12818
+0,1,1.35996e+14,1,1,0,0,-5.79636
+0,1,1.35996e+14,1,1,0,0,12.2196
+0,1,1.35996e+14,1,1,0,0,5.59427
+0,1,1.35996e+14,1,1,0,0,-22.9084
+0,1,1.35996e+14,1,1,0,0,2.70951
+0,1,1.35996e+14,1,1,0,0,-0.604509
+0,1,1.35996e+14,1,1,0,0,1.06201
+0,1,1.35996e+14,1,1,0,0,-3.10986
+0,1,1.35996e+14,1,1,0,0,6.57804
+0,1,1.35996e+14,1,1,0,0,9.0426
+0,1,1.35996e+14,1,1,0,0,3.30854
+0,1,1.35996e+14,1,1,0,0,8.85378
+0,1,1.35996e+14,1,1,0,0,-1.71584
+# 
+#  Elapsed Time: 0 seconds (Warm-up)
+#                0 seconds (Sampling)
+#                0 seconds (Total)
+#