[PATCH v5 2/4] docs, qapi: generate undocumented return sections

[John Snow <jsnow@redhat.com>]

This patch changes the qapidoc parser to generate stub Return value
documentation for any command that has a return value but does not have
a "Returns:" doc section.

The stubs include just the type name, which will be rendered with a
cross-reference link in the HTML output.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 docs/sphinx/qapidoc.py | 14 ++++++++------
 scripts/qapi/parser.py | 34 ++++++++++++++++++++++++++++++++++
 scripts/qapi/schema.py |  3 +++
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/docs/sphinx/qapidoc.py b/docs/sphinx/qapidoc.py
index 8011ac9efaf..77e28a65cfc 100644
--- a/docs/sphinx/qapidoc.py
+++ b/docs/sphinx/qapidoc.py
@@ -255,16 +255,18 @@ def visit_feature(self, section: QAPIDoc.ArgSection) -> None:
     def visit_returns(self, section: QAPIDoc.Section) -> None:
         assert isinstance(self.entity, QAPISchemaCommand)
         rtype = self.entity.ret_type
-        # q_empty can produce None, but we won't be documenting anything
-        # without an explicit return statement in the doc block, and we
-        # should not have any such explicit statements when there is no
-        # return value.
+        # return statements will not be present (and won't be
+        # autogenerated) for any command that doesn't return
+        # *something*, so rtype will always be defined here.
         assert rtype
 
         typ = self.format_type(rtype)
         assert typ
-        assert section.text
-        self.add_field("return", typ, section.text, section.info)
+
+        if section.text:
+            self.add_field("return", typ, section.text, section.info)
+        else:
+            self.add_lines(f":return-nodesc: {typ}", section.info)
 
     def visit_errors(self, section: QAPIDoc.Section) -> None:
         # FIXME: the formatting for errors may be inconsistent and may
diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
index 949d9e8bff7..fc5174e3357 100644
--- a/scripts/qapi/parser.py
+++ b/scripts/qapi/parser.py
@@ -815,6 +815,40 @@ def connect_feature(self, feature: 'QAPISchemaFeature') -> None:
                                % feature.name)
         self.features[feature.name].connect(feature)
 
+    def ensure_returns(self, info: QAPISourceInfo) -> None:
+
+        def _insert_after_kind(
+            kind: QAPIDoc.Kind,
+            new_sect: QAPIDoc.Section
+        ) -> bool:
+            for sect in filter(lambda sect: sect.kind == kind, reversed(
+                    self.all_sections)):
+                idx = self.all_sections.index(sect) + 1
+                self.all_sections.insert(idx, new_sect)
+                return True
+            return False
+
+        if any(s.kind == QAPIDoc.Kind.RETURNS for s in self.all_sections):
+            return
+
+        # Stub "Returns" section for undocumented returns value
+        stub = QAPIDoc.Section(info, QAPIDoc.Kind.RETURNS)
+
+        if any(_insert_after_kind(kind, stub) for kind in (
+                # 1. If arguments, right after those.
+                QAPIDoc.Kind.MEMBER,
+                # 2. Elif errors, right after those.
+                QAPIDoc.Kind.ERRORS,
+                # 3. Elif features, right after those.
+                QAPIDoc.Kind.FEATURE,
+        )):
+            return
+
+        # Otherwise, it should go right after the intro. The intro
+        # is always the first section and is always present (even
+        # when empty), so we can insert directly at index=1 blindly.
+        self.all_sections.insert(1, stub)
+
     def check_expr(self, expr: QAPIExpression) -> None:
         if 'command' in expr:
             if self.returns and 'returns' not in expr:
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index cbe3b5aa91e..3abddea3525 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -1062,6 +1062,9 @@ def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
             if self.arg_type and self.arg_type.is_implicit():
                 self.arg_type.connect_doc(doc)
 
+            if self.ret_type and self.info:
+                doc.ensure_returns(self.info)
+
     def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_command(
-- 
2.48.1