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qapi: add 'if' to top-level expressions

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Accept 'if' key in top-level elements, accepted as string or list of
string type. The following patches will modify the test visitor to
check the value is correctly saved, and generate #if/#endif code (as a
single #if/endif line or a series for a list).

Example of 'if' key:
{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
  'if': 'defined(TEST_IF_STRUCT)' }

The generated code is for now *unconditional*. Later patches generate
the conditionals.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180703155648.11933-2-marcandre.lureau@redhat.com>
[Commit message and Documentation improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Marc-André Lureau 2018-07-03 17:56:35 +02:00 • committed by Markus Armbruster
parent b07cd3e748
commit 967c885108
22 changed files with 146 additions and 6 deletions
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29
docs/devel/qapi-code-gen.txt
View file

@ -744,6 +744,35 @@ Example: Red Hat, Inc. controls redhat.com, and may therefore add a
downstream command __com.redhat_drive-mirror.
=== Configuring the schema ===
The 'struct', 'enum', 'union', 'alternate', 'command' and 'event'
top-level expressions can take an 'if' key. Its value must be a string
or a list of strings. A string is shorthand for a list containing just
that string. The code generated for the top-level expression will then
be guarded by #if COND for each COND in the list.
Example: a conditional struct
{ 'struct': 'IfStruct', 'data': { 'foo': 'int' },
'if': ['defined(CONFIG_FOO)', 'defined(HAVE_BAR)'] }
gets its generated code guarded like this:
#if defined(CONFIG_FOO)
#if defined(HAVE_BAR)
... generated code ...
#endif /* defined(HAVE_BAR) */
#endif /* defined(CONFIG_FOO) */
Please note that you are responsible to ensure that the C code will
compile with an arbitrary combination of conditions, since the
generators are unable to check it at this point.
The presence of 'if' keys in the schema is reflected through to the
introspection output depending on the build configuration.
== Client JSON Protocol introspection ==
Clients of a Client JSON Protocol commonly need to figure out what