Re: [Qemu-devel] [PATCH RFC v2 07/47] qapi: Generate a nicer struct for flat unions

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> On 07/29/2015 01:33 AM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>> 
>>> On 07/01/2015 02:21 PM, Markus Armbruster wrote:
>>>> The struct generated for a flat union is weird: the members of its
>>>> base are at the end, except for the union tag, which is renamed to
>>>> 'kind' and put at the beginning.
>>>
>
>>> Therefore, it might be worth mentioning that avoiding the rename to
>>> 'kind' is a bug fix, not just a nicer struct :)
>> 
>> Cool!  I'll work (a variation of) this test case into my series.
>
> Another name collision bug: our code generates flat unions as:
>
> struct BlockdevOptions {
>     BlockdevDriver driver;
> ...
>     /* End fields inherited from BlockdevOptionsBase. */
>     /* union tag is BlockdevDriver driver */
>     union {
>         void *data;
>         BlockdevOptionsArchipelago *archipelago;
> ...
>
> which means that if we name any of the branches 'data' (that is, if
> 'data' is a member of the enum discriminator), things fail to compile.
> We could probably fix that by naming our dummy branch '_data'.

Works, because schema names should not begin with '_', except for
downstream extensions, which begin with '__RFQDN_'.  We don't enforce
that, however.  I'll include the appended patch.


Subject: [PATCH] qapi: Document flaws in checking of names

We don't actually enforce our "other than downstream extensions [...],
all names should begin with a letter" rule.  Add a FIXME.

We should reject names that differ only in '_' vs. '.'  vs. '-',
because they're liable to clash in generated C.  Add a FIXME.
---
 scripts/qapi.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 4af47ef..e61db30 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -341,6 +341,8 @@ def discriminator_find_enum_define(expr):
 
     return find_enum(discriminator_type)
 
+# FIXME should enforce "other than downstream extensions [...], all
+# names should begin with a letter".
 valid_name = re.compile('^[a-zA-Z_][a-zA-Z0-9_.-]*$')
 def check_name(expr_info, source, name, allow_optional = False,
                enum_member = False):
@@ -367,6 +369,8 @@ def check_name(expr_info, source, name, allow_optional = 
False,
 def add_name(name, info, meta, implicit = False):
     global all_names
     check_name(info, "'%s'" % meta, name)
+    # FIXME should reject names that differ only in '_' vs. '.'
+    # vs. '-', because they're liable to clash in generated C.
     if name in all_names:
         raise QAPIExprError(info,
                             "%s '%s' is already defined"
-- 
2.4.3