Macro expansion leads to a bare expression

[pauluap]

Description

Compile: lwip_stack.c
In file included from ../features/FEATURE_LWIP/lwip-interface/lwip_stack.c:41:0:
../features/FEATURE_LWIP/lwip-interface/lwip_stack.c: In function 'mbed_lwip_bringup_2':
../features/FEATURE_LWIP/lwip-interface/ppp_lwip.h:58:44: warning: statement with no effect [-Wunused-value]
 #define ppp_lwip_disconnect()              ERR_IF
                                            ^
../features/FEATURE_LWIP/lwip-interface/lwip_stack.c:858:21: note: in expansion of macro 'ppp_lwip_disconnect'
                     ppp_lwip_disconnect();
                     ^~~~~~~~~~~~~~~~~~~
../features/FEATURE_LWIP/lwip-interface/ppp_lwip.h:58:44: warning: statement with no effect [-Wunused-value]
 #define ppp_lwip_disconnect()              ERR_IF
                                            ^
../features/FEATURE_LWIP/lwip-interface/lwip_stack.c:875:21: note: in expansion of macro 'ppp_lwip_disconnect'
                     ppp_lwip_disconnect();

                     ^~~~~~~~~~~~~~~~~~~

If the implementation used functions, a function returning a bare value wouldn't be a problem, but here the 'return' is done by macro expansion. Since the value isn't assigned to anything, it turns out to be a bare expression, thus the warning message.

Cast to void to ignore, technique distilled from https://stackoverflow.com/questions/777261/avoiding-unused-variables-warnings-when-using-assert-in-a-release-build

Pull request type

[X] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[0xc0170]

@pauluap Thanks for the contributions, I'll review them today.

Please use PR type, use X to select what PR type is it to clarify the intent in your commits

Second, use master as destination branch, not mbed-os-5.8 (we apply patches when release is prepared).

[pauluap]

I'll definitely use master as the merge target in the future.

I did mark the PR as a fix. Does it need to be at the top of the PR or something?

[kjbracey]

Equivalent changes are already on the feature-emac branch. No objection to having this on master now though - will get overwritten in merge.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1737
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6614/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1371
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6614/

[mbed-ci]

Test : SUCCESS

Build number : 1540
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6614/1540

[0xc0170]

/morph mbed2-build

[0xc0170]

Travis run, but did not report status back. I restarted it https://travis-ci.org/ARMmbed/mbed-os/builds/365358118 but might not still report it back :( We can try close/open

[cmonr]

sigh

Going to close and reopen this to see if we can't get travis-ci to report it's success.

[cmonr]

Interesting.
If I had to bet, I'd say thing will work this time around.

@0xc0170 @pauluap It looks like restarting the ci build wasn't working because the destination branch inside of travis somehow didn't get the message that this PR was change from mbed-os-5.8 to master.
Good to know for the future.

[mbed-ci]

Build : SUCCESS

Build number : 1777
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6614/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : FAILURE

Build number : 1418
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6614/

[mbed-ci]

Exporter Build : FAILURE

Build number : 1418
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6614/

[mbed-ci]

Test : SUCCESS

Build number : 1587
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6614/1587

[0xc0170]

Pipe closed, restarting exporters

/morph export-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1427
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6614/