Interpret 'required' key when present in a reportlets config dictionary.

If its true and no files/figures were found then raise an exception.
Report indexer will catch these exceptions and raise a single exception
at the end of its run with all of the collected reportlet exceptions.

nireports/assembler/report.py

@@ -36,6 +36,7 @@
 
 from nireports.assembler import data
 from nireports.assembler.reportlet import Reportlet
+from nireports.exceptions import NiReportsException, ReportletException
 
 # Add a new figures spec
 try:
@@ -339,6 +340,7 @@ def index(self, config):
 
         This method also places figures in their final location.
         """
+        exceptions = []
         # Initialize a BIDS layout
         _indexer = BIDSLayoutIndexer(
             config_filename=data.load("nipreps.json"),
@@ -361,22 +363,25 @@ def index(self, config):
             orderings = [s for s in subrep_cfg.get("ordering", "").strip().split(",") if s]
             entities, list_combos = self._process_orderings(orderings, layout.get(**bids_filters))
 
+            reportlets = []
+
             if not list_combos:  # E.g. this is an anatomical reportlet
-                reportlets = [
-                    Reportlet(
-                        layout,
-                        config=cfg,
-                        out_dir=out_dir,
-                        bids_filters=bids_filters,
-                        metadata=metadata,
-                    )
-                    for cfg in subrep_cfg["reportlets"]
-                ]
+                for cfg in subrep_cfg["reportlets"]:
+                    try:
+                        rlet = Reportlet(
+                            layout,
+                            config=cfg,
+                            out_dir=out_dir,
+                            bids_filters=bids_filters,
+                            metadata=metadata,
+                        )
+                        reportlets.append(rlet)
+                    except ReportletException as e:
+                        exceptions.append(e) 
                 list_combos = subrep_cfg.get("nested", False)
             else:
                 # Do not use dictionary for queries, as we need to preserve ordering
                 # of ordering columns.
-                reportlets = []
                 for c in list_combos:
                     # do not display entities with the value None.
                     c_filt = [
@@ -389,20 +394,28 @@ def index(self, config):
 
                     for cfg in subrep_cfg["reportlets"]:
                         cfg["bids"].update({entities[i]: c[i] for i in range(len(c))})
-                        rlet = Reportlet(
-                            layout,
-                            config=cfg,
-                            out_dir=out_dir,
-                            bids_filters=bids_filters,
-                            metadata=metadata,
-                        )
-                        if not rlet.is_empty():
-                            rlet.title = title
-                            title = None
-                            reportlets.append(rlet)
+                        try:
+                            rlet = Reportlet(
+                                layout,
+                                config=cfg,
+                                out_dir=out_dir,
+                                bids_filters=bids_filters,
+                                metadata=metadata,
+                            )
+                            if not rlet.is_empty():
+                                rlet.title = title
+                                title = None
+                                reportlets.append(rlet)
+                        except ReportletException as e:
+                            exceptions.append(e)
 
             # Filter out empty reportlets
             reportlets = [r for r in reportlets if not r.is_empty()]
+
+            # When support python < 3.11 dropped we can use ExceptionGroups
+            if exceptions:
+                raise NiReportsException(('There were errors generating report {self}', *exceptions))
+
             if reportlets:
                 sub_report = SubReport(
                     subrep_cfg["name"],
@@ -444,6 +457,9 @@ def process_plugins(self, config, metadata=None):
                         )
                     ],
                 )
+
+    def __str__(self):
+        return f'<Report {self.title}>'
 
     def generate_report(self):
         """Once the Report has been indexed, the final HTML can be generated"""

nireports/assembler/reportlet.py

@@ -32,6 +32,7 @@
 
 from nireports.assembler import data
 from nireports.assembler.misc import dict2html, read_crashfile
+from nireports.exceptions import RequiredReportletException
 
 SVG_SNIPPET = [
     """\
@@ -421,6 +422,10 @@ def __init__(self, layout, config=None, out_dir=None, bids_filters=None, metadat
                     boiler_tabs.append("</ul>")
                     self.components.append(("\n".join(boiler_tabs + boiler_body), desc_text))
 
+        if config.get("required", False) and self.is_empty():
+            raise RequiredReportletException(config)
+
+
     def is_empty(self):
         """Determine whether the reportlet has no components."""
         return len(self.components) == 0

nireports/assembler/tests/test_report.py

@@ -36,6 +36,7 @@
 
 from nireports.assembler import data
 from nireports.assembler.report import Report
+from nireports.exceptions import NiReportsException, RequiredReportletException 
 
 summary_meta = {
     "Summary": {
@@ -138,6 +139,20 @@ def test_report2(bids_sessions):
         subject="01",
     )
 
+def test_missing_reportlet(
+    test_report1,
+    bids_sessions
+):
+    out_dir = tempfile.mkdtemp()
+    report = test_report1
+    settings = yaml.safe_load(data.load.readable("default.yml").read_text())
+    settings["root"] = str(Path(bids_sessions) / "nireports")
+    settings["out_dir"] = str(Path(out_dir) / "nireports")
+    settings["run_uuid"] = "fakeuuid"
+    settings['sections'][0]['reportlets'][0]['required'] = True
+    settings['sections'][0]['reportlets'][0]['bids'] = {'datatype': 'fake'}
+    with pytest.raises(NiReportsException, match='No content found'):
+        report.index(settings)
 
 @pytest.mark.parametrize(
     "orderings,expected_entities,expected_value_combos",

nireports/exceptions.py

@@ -0,0 +1,9 @@
+class NiReportsException(Exception):
+    pass
+
+class ReportletException(NiReportsException):
+    pass
+
+class RequiredReportletException(ReportletException):
+    def __init__(self, config):
+        self.args = (f'No content found while generated reportlet listed as required with the following config: {config}',)