catch syntax error for options and defaults

Author: seungpark

snooty/parser.py

@@ -939,7 +939,19 @@ def handle_composable(self, node: n.ComposableDirective) -> None:
                     )
                     continue
                 ordered_spec_composables.append(composable_from_spec)
-                specified_default_id = default_ids[index]
+                try:
+                    specified_default_id = default_ids[index]
+                except IndexError:
+                    # error to be verbose about default ids not matching up with option ids
+                    self.diagnostics.append(
+                        InvalidChildCount(
+                            "composable-tutorial",
+                            "defaults",
+                            str(len(option_ids)),
+                            node.start[0],
+                        )
+                    )
+                    continue
                 allowed_values_dict = {
                     option.id: option for option in composable_from_spec.options
                 }

snooty/test_postprocess.py

@@ -18,6 +18,7 @@
     GuideAlreadyHasChapter,
     InvalidChapter,
     InvalidChild,
+    InvalidChildCount,
     InvalidContextError,
     InvalidIAEntry,
     InvalidIALinkedData,
@@ -4272,6 +4273,26 @@ def test_composable_tutorial_errors() -> None:
             MissingChild,
         ]
 
+    with make_test(
+        {
+            Path(
+                "source/index.txt"
+            ): """
+.. composable-tutorial::
+   :options: interface, language, cluster-topology, cloud-provider
+   :defaults: driver, None, repl
+
+   .. selected-content::
+      :selections: driver, None, repl
+        """
+        }
+    ) as result:
+        diagnostics = result.diagnostics[FileId("index.txt")]
+        assert len(diagnostics) == 1
+        assert [type(d) for d in diagnostics] == [
+            InvalidChildCount,
+        ]
+
 
 def test_composable_headings() -> None:
     with make_test(