[Libguestfs] [PATCH nbdkit] golang: Compile against the local nbdkit build, not installed.

[Eric Blake]

On 4/23/20 11:58 AM, Daniel P. Berrangé wrote:
> On Thu, Apr 23, 2020 at 05:55:14PM +0100, Richard W.M. Jones wrote:
>> When compiling when an older nbdkit is installed, the build would fail
>> because certain symbols such as .get_ready were not defined:
>>
>>    ../../src/libguestfs.org/nbdkit/nbdkit.go:541:8: plugin.get_ready undefined (type _Ctype_struct_nbdkit_plugin has no field or method get_ready)
>>
>> This happens because we were using the installed <nbdkit-plugin.h>
>> rather than the local copy.
>>
>> We don't want to modify the *.go files themselves as they might be
>> copied into other projects.  Instead we can set PKG_CONFIG to point to
>> a fake pkg-config binary which will return the correct CFLAGS.
>>
>> Fixes: commit 1ff44288ae1cf95428283e252edd9474c3fe3b55
>> Thanks: Dan Berrangé, Eric Blake
> 
>> +# This fake pkg-config program is used to trick cgo so that
>> +# "#cgo pkg-config nbdkit" lines are processed relative to the local
>> +# directory and not the installed nbdkit.
>> +
>> +case "$1" in
>> +    --cflags*) echo "-I at abs_top_builddir@/include" ;;
>> +    *) ;;
>> +esac
> 
> Don't you need something like this too:
> 
>     --libs)  echo "-L at abs_top_builddir@/lib -lnbdkit"

Also, if you're installing this in PATH prior to the real pkg-config, 
shouldn't you start by checking whether 'nbdkit' is one of the 
arguments?  If so, fall through to the 'case "$1"' code, if not, 
short-circuit into 'exec /path/to/pkg-config "$@"', so that whatever 
_other_ pkg-config queries cgo makes will be answered as usual?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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