[Libguestfs] [PATCH nbdkit 2/2] tests: Test that public headers are ANSI (ISO C90) compatible.

[Eric Blake]

On 1/14/19 6:15 AM, Richard W.M. Jones wrote:
> In commit 3775916120749e935d287f35cb29ff6c586656df (and before that in
> discussions with Eric) we decided that we should try to allow plugins
> to be compiled with C compilers other than GCC or Clang (or with very
> old / peculiar / incompatible versions of those compilers).
> 
> However until we test this we cannot guarantee that changes to the
> code will not break this in future, hence this test.
> 
> Note that GCC or Clang is still required to compile nbdkit itself.
> ---
>  tests/test-ansi-c-plugin.c | 167 +++++++++++++++++++++++++++++++++++++
>  tests/Makefile.am          |  24 ++++++
>  tests/test-ansi-c.sh       |  39 +++++++++
>  3 files changed, 230 insertions(+)
> 
> diff --git a/tests/test-ansi-c-plugin.c b/tests/test-ansi-c-plugin.c
> new file mode 100644
> index 0000000..8596ca5
> --- /dev/null
> +++ b/tests/test-ansi-c-plugin.c

> +
> +#include <config.h>

Do we really want to be including <config.h> in this file?  This is the
one case where we know we are standalone; I'm also worried that the
macros defined in config.h were determined based on the existence of
extensions during configure probes, and may be inaccurately-defined for
compilation under a different set of compiler flags.  I'd omit this (but
perhaps leave a comment why), as proof that we are truly independent of
how nbdkit was configured.

> +/* Strictly speaking (and we're compiling with -pedantic, so we _are_

lol

> + * strictly speaking), ANSI C did not allow struct initialization
> + * using labels.  However it was a common extension to C compilers of
> + * the period.
> + *
> + * Therefore we rely here on the order of fields in struct
> + * nbdkit_plugin.  But that's OK because of nbdkit's stable ABI
> + * guarantee.
> + *
> + * If you are really writing an nbdkit plugin which can only use C90
> + * then you are advised to find the extension to your compiler which
> + * allows you to initialize named fields.
> + */
> +static struct nbdkit_plugin plugin = {
> +  0, 0, 0,

I'd typically use NULL for pointers, but using 0 is strictly portable,
so I'm fine with it.

> +  "ansic",
> +  0,
> +  PACKAGE_VERSION,
> +  0,
> +  ansi_c_load,
> +  0,
> +  0, 0, 0,
> +  ansi_c_open,
> +  0,
> +  ansi_c_get_size,
> +  0, 0, 0, 0,
> +  ansi_c_pread
> +};
> +
> +NBDKIT_REGISTER_PLUGIN(plugin)

> +++ b/tests/Makefile.am

>  
> +# This builds a plugin using an ANSI (ISO C90) compiler to ensure that
> +# the header file is compatible.  The plugin does nothing very
> +# interesting, it's mainly a compile test.
> +TESTS += \
> +	test-ansi-c.sh
> +# check_LTLIBRARIES won't build a shared library (see automake manual).
> +# So we have to do this and add a dependency.
> +noinst_LTLIBRARIES += test-ansi-c-plugin.la
> +test-ansi-c.sh: test-ansi-c-plugin.la
> +
> +test_ansi_c_plugin_la_SOURCES = \
> +	test-ansi-c-plugin.c \
> +	$(top_srcdir)/include/nbdkit-plugin.h
> +test_ansi_c_plugin_la_CPPFLAGS = \
> +	-std=c90 -pedantic \
> +	-I$(top_srcdir)/include
> +test_ansi_c_plugin_la_CFLAGS = \
> +        $(WARNINGS_CFLAGS)
> +# For use of the -rpath option, see:
> +# https://lists.gnu.org/archive/html/libtool/2007-07/msg00067.html
> +test_ansi_c_plugin_la_LDFLAGS = \
> +	-module -avoid-version -shared -rpath /nowhere

Looks sane, if it still works without <config.h>.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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