[RFC,15/18] qapi: Support empty modules

If you added an include file that doesn't contain any definitions, no
source files would be generated for it. However, in other source files,
you would still get an #include for the header files of the empty
module.

The intended behaviour is that empty source files are created for empty
modules. This patch makes QAPISchema keep a list of all modules
(including empty ones) and modifies visit() to first visit all modules
in that list.

Some test reference outputs need to be updated due to the additional
visitor calls.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 scripts/qapi/schema.py                   | 9 +++++++++
 tests/qapi-schema/comments.out           | 2 ++
 tests/qapi-schema/doc-bad-section.out    | 2 ++
 tests/qapi-schema/doc-good.out           | 2 ++
 tests/qapi-schema/empty.out              | 2 ++
 tests/qapi-schema/event-case.out         | 2 ++
 tests/qapi-schema/include-repetition.out | 4 ++++
 tests/qapi-schema/include-simple.out     | 3 +++
 tests/qapi-schema/indented-expr.out      | 2 ++
 tests/qapi-schema/qapi-schema-test.out   | 4 ++++
 10 files changed, 32 insertions(+)

Kevin Wolf <kwolf@redhat.com> writes:

> If you added an include file that doesn't contain any definitions, no
> source files would be generated for it. However, in other source files,
> you would still get an #include for the header files of the empty
> module.

Bug.

Cause: we generate #include module.h always, and the module.h when
visiting its first definition.  If there are no definitions, we don't.

> The intended behaviour is that empty source files are created for empty
> modules.

Yes.

>          This patch makes QAPISchema keep a list of all modules
> (including empty ones) and modifies visit() to first visit all modules
> in that list.

Minimally invasive fix.  Backends still initialize module output on
first visit_module(), but now all modules are visited upfront.

Separating "initialize module" from "switch to module" might be easier
to understand.  Idea, not demand.

> Some test reference outputs need to be updated due to the additional
> visitor calls.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  scripts/qapi/schema.py                   | 9 +++++++++
>  tests/qapi-schema/comments.out           | 2 ++
>  tests/qapi-schema/doc-bad-section.out    | 2 ++
>  tests/qapi-schema/doc-good.out           | 2 ++
>  tests/qapi-schema/empty.out              | 2 ++
>  tests/qapi-schema/event-case.out         | 2 ++
>  tests/qapi-schema/include-repetition.out | 4 ++++
>  tests/qapi-schema/include-simple.out     | 3 +++
>  tests/qapi-schema/indented-expr.out      | 2 ++
>  tests/qapi-schema/qapi-schema-test.out   | 4 ++++
>  10 files changed, 32 insertions(+)
>
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index 38041098bd..e1b034d67d 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -749,6 +749,7 @@ class QAPISchema(object):
>          self.docs = parser.docs
>          self._entity_list = []
>          self._entity_dict = {}
> +        self._modules = [os.path.basename(fname)]
>          self._predefining = True
>          self._def_predefineds()
>          self._predefining = False
> @@ -800,6 +801,8 @@ class QAPISchema(object):
>              main_info = main_info.parent
>          fname = os.path.relpath(include, os.path.dirname(main_info.fname))
>          self._def_entity(QAPISchemaInclude(fname, info))
> +        if fname not in self._modules:
> +            self._modules.append(fname)
>  
>      def _def_builtin_type(self, name, json_type, c_type):
>          self._def_entity(QAPISchemaBuiltinType(name, json_type, c_type))
> @@ -1033,6 +1036,12 @@ class QAPISchema(object):
>          visitor.visit_begin(self)
>          module = None
>          visitor.visit_module(module)
> +
> +        # Make sure that all modules are visited, even if they contain no
> +        # entities
> +        for module in self._modules:
> +            visitor.visit_module(module)
> +

Slightly neater, I think:

           visitor.visit_begin(self)
  +
  +        # Visit all modules, to ensure @visitor sees them
  +        for module in self._modules:
  +            visitor.visit_module(module)
  +
           module = None
           visitor.visit_module(module)

This way, we keep starting with module None rather than whatever user
module comes last.  The .out diffs below then don't add a nother "module
None" line.

>          for entity in self._entity_list:
>              if visitor.visit_needed(entity):
>                  if entity.module != module:
> diff --git a/tests/qapi-schema/comments.out b/tests/qapi-schema/comments.out
> index 273f0f54e1..fa7e95d1cc 100644
> --- a/tests/qapi-schema/comments.out
> +++ b/tests/qapi-schema/comments.out
> @@ -1,4 +1,6 @@
>  module None
> +module comments.json
> +module None
>  object q_empty
>  enum QType
>      prefix QTYPE
[...]