Backport: Fix read_from_file error propagation

src/ert/config/gen_data_config.py

@@ -150,10 +150,11 @@ def _read_file(filename: Path, report_step: int) -> xr.Dataset:
                     except ValueError as err:
                         errors.append(str(err))
 
-            ds_all_report_steps = xr.concat(
-                datasets_per_report_step, dim="report_step"
-            ).expand_dims(name=[name])
-            datasets_per_name.append(ds_all_report_steps)
+            if len(datasets_per_report_step) > 0:
+                ds_all_report_steps = xr.concat(
+                    datasets_per_report_step, dim="report_step"
+                ).expand_dims(name=[name])
+                datasets_per_name.append(ds_all_report_steps)
 
         if errors:
             raise ValueError(f"Error reading GEN_DATA: {self.name}, errors: {errors}")

tests/unit_tests/config/test_gen_data_config.py

@@ -59,3 +59,30 @@ def test_malformed_or_missing_gen_data_result_file(result_file, error_message):
             GenDataConfig.from_config_dict({"GEN_DATA": [config_line.split()]})
     else:
         GenDataConfig.from_config_dict({"GEN_DATA": [config_line.split()]})
+
+
+def test_that_invalid_gendata_outfile_error_propagates(tmp_path):
+    (tmp_path / "poly.out").write_text("""
+        4.910405046410615,4.910405046410615
+        6.562317389289953,6.562317389289953
+        9.599763191512997,9.599763191512997
+        14.022742453079745,14.022742453079745
+        19.831255173990197,19.831255173990197
+        27.025301354244355,27.025301354244355
+        35.604880993842215,35.604880993842215
+        45.56999409278378,45.56999409278378
+        56.92064065106905,56.92064065106905
+        69.65682066869802,69.65682066869802
+    """)
+
+    config = GenDataConfig(
+        name="gen_data",
+        keys=["something"],
+        report_steps_list=[None],
+        input_files=["poly.out"],
+    )
+    with pytest.raises(
+        ValueError,
+        match="Error reading GEN_DATA.*could not convert string.*4.910405046410615,4.910405046410615.*to float64",
+    ):
+        config.read_from_file(tmp_path, 0)