Re: [PATCH v3 2/3] qapi: Do not generate empty enum

[Philippe Mathieu-Daudé]

On 16/3/23 15:57, Markus Armbruster wrote:
Daniel P. Berrangé <berra...@redhat.com> writes:
On Thu, Mar 16, 2023 at 01:31:04PM +0100, Markus Armbruster wrote:
Philippe Mathieu-Daudé <phi...@linaro.org> writes:

Per the C++ standard, empty enum are ill-formed. Do not generate

The C standard.  The C++ standard doesn't apply here :)

I can't find how empty enums are considered by the C standard...

But all of this falls apart with conditional members!

Example 1 (taken from qapi/block-core.json):

     { 'enum': 'BlockdevAioOptions',
       'data': [ 'threads', 'native',
                 { 'name': 'io_uring', 'if': 'CONFIG_LINUX_IO_URING' } ] }

Generates now:

     typedef enum BlockdevAioOptions {
         BLOCKDEV_AIO_OPTIONS_THREADS,
         BLOCKDEV_AIO_OPTIONS_NATIVE,
     #if defined(CONFIG_LINUX_IO_URING)
         BLOCKDEV_AIO_OPTIONS_IO_URING,
     #endif /* defined(CONFIG_LINUX_IO_URING) */
         BLOCKDEV_AIO_OPTIONS__MAX,
     } BlockdevAioOptions;

BLOCKDEV_AIO_OPTIONS__MAX is 3 if defined(CONFIG_LINUX_IO_URING), else
2.

After the next patch:

     typedef enum BlockdevAioOptions {
         BLOCKDEV_AIO_OPTIONS_THREADS,
         BLOCKDEV_AIO_OPTIONS_NATIVE,
     #if defined(CONFIG_LINUX_IO_URING)
         BLOCKDEV_AIO_OPTIONS_IO_URING,
     #endif /* defined(CONFIG_LINUX_IO_URING) */
     #define BLOCKDEV_AIO_OPTIONS__MAX 3
     } BlockdevAioOptions;

Now it's always 3.

Good catch... Using:

-- >8 --
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
@@ -110,8 +110,11 @@ def gen_enum(name: str,

     ret += mcgen('''
 } %(c_name)s;
+_Static_assert(%(c_last_enum)s == %(c_length)s - 1, "%(c_name)s");
 ''',
-                 c_name=c_name(name))
+                 c_name=c_name(name),
+                 c_last_enum=c_enum_const(name, members[-1].name, prefix),
+                 c_length=len(members))

     ret += mcgen('''
---

I get:

./qapi/qapi-types-block-core.h:355:1: error: static_assert failed due to 
requirement 'BLOCKDEV_AIO_OPTIONS_NATIVE == 3 - 1' "BlockdevAioOptions"
_Static_assert(BLOCKDEV_AIO_OPTIONS_IO_URING == 3 - 1, 
"BlockdevAioOptions");
^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./qapi/qapi-types-block-core.h:430:1: error: static_assert failed due to 
requirement 'BLOCKDEV_DRIVER_VVFAT == 47 - 1' "BlockdevDriver"
_Static_assert(BLOCKDEV_DRIVER_VVFAT == 47 - 1, "BlockdevDriver");
^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./qapi/qapi-types-char.h:110:1: error: static_assert failed due to 
requirement 'CHARDEV_BACKEND_KIND_MEMORY == 22 - 1' "ChardevBackendKind"
_Static_assert(CHARDEV_BACKEND_KIND_MEMORY == 22 - 1, "ChardevBackendKind");
^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...