Many implicit-fallthrough errors

[yelkarama]

I did this

Building the latest release of curl (7.77) on RHEL6 using newly built gcc toolchain (git: 12.0.0)
When using Werror, I'm getting these many implicit-fallthrough error:

>[21/206] Building C object lib/CMakeFiles/libcurl.dir/content_encoding.c.o
FAILED: lib/CMakeFiles/libcurl.dir/content_encoding.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/content_encoding.c.o -MF lib/CMakeFiles/libcurl.dir/content_encoding.c.o.d -o lib/CMakeFiles/libcurl.dir/content_encoding.c.o -c ../lib/content_encoding.c
../lib/content_encoding.c: In function 'inflate_stream':
../lib/content_encoding.c:230:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
  230 |       if(zp->zlib_init == ZLIB_INIT) {
      |         ^
../lib/content_encoding.c:244:5: note: here
  244 |     default:
      |     ^~~~~~~
cc1: all warnings being treated as errors
[23/206] Building C object lib/CMakeFiles/libcurl.dir/cookie.c.o
FAILED: lib/CMakeFiles/libcurl.dir/cookie.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/cookie.c.o -MF lib/CMakeFiles/libcurl.dir/cookie.c.o.d -o lib/CMakeFiles/libcurl.dir/cookie.c.o -c ../lib/cookie.c
../lib/cookie.c: In function 'Curl_cookie_add':
../lib/cookie.c:899:15: error: this statement may fall through [-Werror=implicit-fallthrough=]
  899 |         fields++; /* add a field and fall down to secure */
      |         ~~~~~~^~
../lib/cookie.c:901:7: note: here
  901 |       case 3:
      |       ^~~~
cc1: all warnings being treated as errors
[45/206] Building C object lib/CMakeFiles/libcurl.dir/ftp.c.o
FAILED: lib/CMakeFiles/libcurl.dir/ftp.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/ftp.c.o -MF lib/CMakeFiles/libcurl.dir/ftp.c.o.d -o lib/CMakeFiles/libcurl.dir/ftp.c.o -c ../lib/ftp.c
../lib/ftp.c: In function 'ftp_done':
../lib/ftp.c:3216:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
 3216 |     if(!premature)
      |       ^
../lib/ftp.c:3222:3: note: here
 3222 |   default:       /* by default, an error means the control connection is
      |   ^~~~~~~
cc1: all warnings being treated as errors
[57/206] Building C object lib/CMakeFiles/libcurl.dir/formdata.c.o
FAILED: lib/CMakeFiles/libcurl.dir/formdata.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/formdata.c.o -MF lib/CMakeFiles/libcurl.dir/formdata.c.o.d -o lib/CMakeFiles/libcurl.dir/formdata.c.o -c ../lib/formdata.c
../lib/formdata.c: In function 'FormAdd':
../lib/formdata.c:278:27: error: this statement may fall through [-Werror=implicit-fallthrough=]
  278 |       current_form->flags |= HTTPPOST_PTRNAME; /* fall through */
      |       ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
../lib/formdata.c:281:5: note: here
  281 |     case CURLFORM_COPYNAME:
      |     ^~~~
../lib/formdata.c:305:27: error: this statement may fall through [-Werror=implicit-fallthrough=]
  305 |       current_form->flags |= HTTPPOST_PTRCONTENTS;
      |       ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
../lib/formdata.c:307:5: note: here
  307 |     case CURLFORM_COPYCONTENTS:
      |     ^~~~
cc1: all warnings being treated as errors
[61/206] Building C object lib/CMakeFiles/libcurl.dir/http_ntlm.c.o
FAILED: lib/CMakeFiles/libcurl.dir/http_ntlm.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/http_ntlm.c.o -MF lib/CMakeFiles/libcurl.dir/http_ntlm.c.o.d -o lib/CMakeFiles/libcurl.dir/http_ntlm.c.o -c ../lib/http_ntlm.c
../lib/http_ntlm.c: In function 'Curl_output_ntlm':
../lib/http_ntlm.c:252:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
  252 |     *state = NTLMSTATE_LAST;
      |     ~~~~~~~^~~~~~~~~~~~~~~~
../lib/http_ntlm.c:254:3: note: here
  254 |   case NTLMSTATE_LAST:
      |   ^~~~
cc1: all warnings being treated as errors
[73/206] Building C object lib/CMakeFiles/libcurl.dir/http.c.o
FAILED: lib/CMakeFiles/libcurl.dir/http.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/http.c.o -MF lib/CMakeFiles/libcurl.dir/http.c.o.d -o lib/CMakeFiles/libcurl.dir/http.c.o -c ../lib/http.c
../lib/http.c: In function 'Curl_http_statusline':
../lib/http.c:3746:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
 3746 |     if(data->set.timecondition)
      |       ^
../lib/http.c:3749:3: note: here
 3749 |   case 204:
      |   ^~~~
cc1: all warnings being treated as errors
[77/206] Building C object lib/CMakeFiles/libcurl.dir/mqtt.c.o
FAILED: lib/CMakeFiles/libcurl.dir/mqtt.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/mqtt.c.o -MF lib/CMakeFiles/libcurl.dir/mqtt.c.o.d -o lib/CMakeFiles/libcurl.dir/mqtt.c.o -c ../lib/mqtt.c
../lib/mqtt.c: In function 'mqtt_doing':
../lib/mqtt.c:575:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  575 |     mqstate(data, MQTT_REMAINING_LENGTH, MQTT_NOSTATE);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../lib/mqtt.c:577:3: note: here
  577 |   case MQTT_REMAINING_LENGTH:
      |   ^~~~
../lib/mqtt.c: In function 'mqtt_read_publish':
../lib/mqtt.c:483:17: error: this statement may fall through [-Werror=implicit-fallthrough=]
  483 |     mq->npacket = remlen; /* get this many bytes */
      |     ~~~~~~~~~~~~^~~~~~~~
../lib/mqtt.c:485:3: note: here
  485 |   case MQTT_PUB_REMAIN: {
      |   ^~~~
cc1: all warnings being treated as errors
[82/206] Building C object lib/CMakeFiles/libcurl.dir/multi.c.o
FAILED: lib/CMakeFiles/libcurl.dir/multi.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/multi.c.o -MF lib/CMakeFiles/libcurl.dir/multi.c.o.d -o lib/CMakeFiles/libcurl.dir/multi.c.o -c ../lib/multi.c
../lib/multi.c: In function 'Curl_update_timer':
../lib/multi.c:3199:64: error: '?:' using integer constants in boolean context [-Werror=int-in-bool-context]
 3199 |     if(Curl_splaycomparekeys(none, multi->timer_lastcall)) {
      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~   ^                                                                                                                                                                                      
cc1: all warnings being treated as errors
[90/206] Building C object lib/CMakeFiles/libcurl.dir/mprintf.c.o
FAILED: lib/CMakeFiles/libcurl.dir/mprintf.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/mprintf.c.o -MF lib/CMakeFiles/libcurl.dir/mprintf.c.o.d -o lib/CMakeFiles/libcurl.dir/mprintf.c.o -c ../lib/mprintf.c
../lib/mprintf.c: In function 'dprintf_Pass1':
../lib/mprintf.c:362:13: error: this statement may fall through [-Werror=implicit-fallthrough=]
  362 |           if(!(flags & FLAGS_LEFT))
      |             ^
../lib/mprintf.c:365:9: note: here
  365 |         case '1': case '2': case '3': case '4':
      |         ^~~~
../lib/mprintf.c:399:15: error: this statement may fall through [-Werror=implicit-fallthrough=]
  399 |         flags |= FLAGS_ALT;
      |         ~~~~~~^~~~~~~~~~~~
../lib/mprintf.c:401:7: note: here
  401 |       case 's':
      |       ^~~~
cc1: all warnings being treated as errors
[99/206] Building C object lib/CMakeFiles/libcurl.dir/socks.c.o
FAILED: lib/CMakeFiles/libcurl.dir/socks.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/socks.c.o -MF lib/CMakeFiles/libcurl.dir/socks.c.o.d -o lib/CMakeFiles/libcurl.dir/socks.c.o -c ../lib/socks.c
../lib/socks.c: In function 'Curl_SOCKS4':
../lib/socks.c:262:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
  262 |     if(dns) {
      |       ^
../lib/socks.c:279:3: note: here
  279 |   CONNECT_RESOLVED:
      |   ^~~~~~~~~~~~~~~~
../lib/socks.c:280:26: error: this statement may fall through [-Werror=implicit-fallthrough=]
  280 |   case CONNECT_RESOLVED: {
      |                          ^
../lib/socks.c:317:3: note: here
  317 |   CONNECT_REQ_INIT:
      |   ^~~~~~~~~~~~~~~~
../lib/socks.c:359:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
  359 |       sxstate(data, CONNECT_REQ_SENDING);
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:362:3: note: here
  362 |   case CONNECT_REQ_SENDING:
      |   ^~~~
../lib/socks.c:380:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  380 |     sxstate(data, CONNECT_SOCKS_READ);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:383:3: note: here
  383 |   case CONNECT_SOCKS_READ:
      |   ^~~~
../lib/socks.c: In function 'Curl_SOCKS5':
../lib/socks.c:584:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
  584 |     if(written != sx->outstanding) {
      |       ^
../lib/socks.c:591:3: note: here
  591 |   CONNECT_SOCKS_READ_INIT:
      |   ^~~~~~~~~~~~~~~~~~~~~~~
../lib/socks.c:594:14: error: this statement may fall through [-Werror=implicit-fallthrough=]
  594 |     sx->outp = socksreq; /* store it here */
      |     ~~~~~~~~~^~~~~~~~~~
../lib/socks.c:596:3: note: here
  596 |   case CONNECT_SOCKS_READ:
      |   ^~~~
../lib/socks.c:706:14: error: this statement may fall through [-Werror=implicit-fallthrough=]
  706 |     sx->outp = socksreq;
      |     ~~~~~~~~~^~~~~~~~~~
../lib/socks.c:709:3: note: here
  709 |   case CONNECT_AUTH_SEND:
      |   ^~~~
../lib/socks.c:724:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  724 |     sxstate(data, CONNECT_AUTH_READ);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:726:3: note: here
  726 |   case CONNECT_AUTH_READ:
      |   ^~~~
../lib/socks.c:752:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  752 |     sxstate(data, CONNECT_REQ_INIT);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:754:3: note: here
  754 |   CONNECT_REQ_INIT:
      |   ^~~~~~~~~~~~~~~~
../lib/socks.c:784:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
  784 |     if(!dns) {
      |       ^
../lib/socks.c:793:3: note: here
  793 |   CONNECT_RESOLVED:
      |   ^~~~~~~~~~~~~~~~
../lib/socks.c:856:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
  856 |     if(!socks5_resolve_local) {
      |       ^
../lib/socks.c:866:3: note: here
  866 |   CONNECT_REQ_SEND:
      |   ^~~~~~~~~~~~~~~~
../lib/socks.c:881:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  881 |     sxstate(data, CONNECT_REQ_SENDING);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:883:3: note: here
  883 |   case CONNECT_REQ_SENDING:
      |   ^~~~
../lib/socks.c:904:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
  904 |     sxstate(data, CONNECT_REQ_READ);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
../lib/socks.c:906:3: note: here
  906 |   case CONNECT_REQ_READ:
      |   ^~~~
../lib/socks.c:992:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
  992 |       if(len > 10) {
      |         ^
../lib/socks.c:1005:3: note: here
 1005 |   case CONNECT_REQ_READ_MORE:
      |   ^~~~
cc1: all warnings being treated as errors
[105/206] Building C object lib/CMakeFiles/libcurl.dir/mime.c.o
FAILED: lib/CMakeFiles/libcurl.dir/mime.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/mime.c.o -MF lib/CMakeFiles/libcurl.dir/mime.c.o.d -o lib/CMakeFiles/libcurl.dir/mime.c.o -c ../lib/mime.c
../lib/mime.c: In function 'encoder_base64_read':
../lib/mime.c:467:11: error: this statement may fall through [-Werror=implicit-fallthrough=]
  467 |         i = (st->buf[st->bufbeg + 1] & 0xFF) << 8;
      |         ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../lib/mime.c:469:7: note: here
  469 |       case 1:
      |       ^~~~
../lib/mime.c: In function 'readback_part':
../lib/mime.c:966:11: error: this statement may fall through [-Werror=implicit-fallthrough=]
  966 |         if(part->kind == MIMEKIND_FILE && part->fp) {
      |           ^
../lib/mime.c:971:7: note: here
  971 |       case CURL_READFUNC_ABORT:
      |       ^~~~
../lib/mime.c:924:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
  924 |       if(match_header(hdr, "Content-Type", 12)) {
      |         ^
../lib/mime.c:929:5: note: here
  929 |     case MIMESTATE_CURLHEADERS:
      |     ^~~~
../lib/mime.c: In function 'read_part_content':
../lib/mime.c:804:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
  804 |       if(part->fp && feof(part->fp))
      |         ^
../lib/mime.c:807:5: note: here
  807 |     default:
      |     ^~~~~~~
cc1: all warnings being treated as errors
[114/206] Building C object lib/CMakeFiles/libcurl.dir/telnet.c.o
FAILED: lib/CMakeFiles/libcurl.dir/telnet.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/telnet.c.o -MF lib/CMakeFiles/libcurl.dir/telnet.c.o.d -o lib/CMakeFiles/libcurl.dir/telnet.c.o -c ../lib/telnet.c
../lib/telnet.c: In function 'telnet_do':
../lib/telnet.c:1495:22: error: this statement may fall through [-Werror=implicit-fallthrough=]
 1495 |       pfd[1].revents = 0;
      |       ~~~~~~~~~~~~~~~^~~
../lib/telnet.c:1497:5: note: here
 1497 |     default:                    /* read! */
      |     ^~~~~~~
cc1: all warnings being treated as errors
[115/206] Building C object lib/CMakeFiles/libcurl.dir/urlapi.c.o
FAILED: lib/CMakeFiles/libcurl.dir/urlapi.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/urlapi.c.o -MF lib/CMakeFiles/libcurl.dir/urlapi.c.o.d -o lib/CMakeFiles/libcurl.dir/urlapi.c.o -c ../lib/urlapi.c
../lib/urlapi.c: In function 'strlen_url':
../lib/urlapi.c:162:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
  162 |       left = FALSE;
../lib/urlapi.c:164:5: note: here
  164 |     default:
      |     ^~~~~~~
../lib/urlapi.c: In function 'strcpy_url':
../lib/urlapi.c:207:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
  207 |       left = FALSE;
../lib/urlapi.c:209:5: note: here
  209 |     default:
      |     ^~~~~~~
cc1: all warnings being treated as errors
[152/206] Building C object lib/CMakeFiles/libcurl.dir/vtls/openssl.c.o
FAILED: lib/CMakeFiles/libcurl.dir/vtls/openssl.c.o 
/usr/lib/ccache/bin/gcc -DBUILDING_LIBCURL -DCURL_HIDDEN_SYMBOLS -DHAVE_CONFIG_H -I../include -Ilib/../include -I../lib/.. -I../lib/../include -Ilib/.. -I../lib -Ilib -isystem /var/data/gcc12gnu212/x86_64-linux-gnu/sysroot/usr/include -Ofast -s -fPIC -pipe -DNDEBUG -march=x86-64 -Wl,--strip-debug,--strip-all -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wno-long-long -Wno-multichar -Wno-format-nonliteral -Wno-sign-conversion -Wno-system-headers -Werror -O3 -DNDEBUG -fvisibility=hidden -MD -MT lib/CMakeFiles/libcurl.dir/vtls/openssl.c.o -MF lib/CMakeFiles/libcurl.dir/vtls/openssl.c.o.d -o lib/CMakeFiles/libcurl.dir/vtls/openssl.c.o -c ../lib/vtls/openssl.c
../lib/vtls/openssl.c: In function 'cert_stuff':
../lib/vtls/openssl.c:998:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
  998 |       if(cert_done)
      |         ^
../lib/vtls/openssl.c:1001:5: note: here
 1001 |     case SSL_FILETYPE_ASN1:
      |     ^~~~
cc1: all warnings being treated as errors
[154/206] Building C object lib/CMakeFiles/libcurl.dir/url.c.o
ninja: build stopped: cannot make progress due to previous errors.

I expected the following

Successful build

curl/libcurl version

7.77

operating system

Linux localhost.localdomain 2.6.32-754.35.1.el6.x86_64 #1 SMP Sat Nov 7 12:42:14 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

[dfandrich]

Technically, they're implicit-fallthrough warnings. It's your configuration that's treating them as errors. That's probably not a good idea for third-party source code over which you don't have direct control.

[bagder]

Are not all of these places marked with /* FALLTHROUGH */ comments accordingly? I would argue that gcc should not complain when we have marked them like that.

[vszakats]

Not long ago the /* FALLTHROUGH */-style tagging started to be replaced by different methods (e.g. __attribute__((__fallthrough__)) in gcc/llvm, and since then these newer releases also ignore this comment. I can't cite exact version numbers unfortunately.

Ref with some details: https://www.kernel.org/doc/html/v5.7/process/deprecated.html#implicit-switch-case-fall-through

[bagder]

(What a weird behavior-breaking change.) So we'll need both the comment and a new creative way to define that attribute for the compilers that insist on that method...

[bagder]

@yelkarama, are you interested in working on a fix for this?

[jzakrzewski]

I'd expect this (WIP) page to list such a breaking change. I also was unable to locate a commit that may introduce such change. Maybe it's some kind of bug in gcc (the gcc12 cycle has just begun)?

[bagder]

I did a first take on using the attribute - in #7302

[vszakats]

[ Looks like this feature first appeared in GCC 7 with support for the attribute and various flavours of comments, configurable via the -Wimplicit-fallthrough[=mode] option. LLVM later added support for the attribute first (~2019), then for comments (~2020). ]

[bagder]

Based on the results of my attempt to fix this, I think we might instead rather decide to stick with the comment version for the time being. There doesn't even seem to be a reliable way to silence these warnings using the attribute method in our CI, so I can't even start to fathom how spectacularly it'll fail at users' places if we'd decide to ship that.

@yelkarama I propose you tell your compiler to accept the comments as fallthrough-indicators.

[vszakats]

@bagder: It indeed looks like a hot mess. Tried digging up info about the default warning mode in GCC, but the documentation wasn't helpful there. The LLVM doc is even less talkative and for some reason lists this option as far back as clang 4.0.0 (early 2017). The end result when doing an actual build is rather accidental. It's less than ideal because otherwise this warning (when justified) is useful.