If configure is run with --disable-gnutls, compilation will fail in oauth2.c, sample failure (similar on master, 4.1.0, 3.19.0):
make[4]: Entering directory '/var/tmp/portage/mail-client/claws-mail-4.1.0-r1/work/claws-mail-4.1.0/src'
gcc -DHAVE_CONFIG_H -I. -I..  -DG_LOG_DOMAIN=\"Claws-Mail\" -DLOCALEDIR=\""/usr/local/share/locale"\" -DPIXMAP_DIR=\""/usr/local/share/icons/hicolor/48x48/apps"\" -DMANUALDIR=\""/usr/local/share/doc/claws-mail/manual"\" -DTARGET_ALIAS=\""x86_64-pc-linux-gnu"\" -DSYSCONFDIR=\""/usr/local/etc"\" -DDATAROOTDIR=\""/usr/local/share"\" -I./common -Icommon -I./gtk -I./etpan -I/usr/include/enchant-2 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -pthread  -I/usr/include/gtk-3.0 -I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/lib64/libffi/include -I/usr/include/harfbuzz -I/usr/include/freetype2 -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/fribidi -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/gio-unix-2.0 -I/usr/include/atk-1.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/dbus-1.0 -I/usr/lib64/dbus-1.0/include -I/usr/include/at-spi-2.0 -pthread  -DGTK_DISABLE_SINGLE_INCLUDES -DGSEAL_ENABLE    -I/usr/include/startup-notification-1.0  -I/usr/include/dbus-1.0 -I/usr/lib64/dbus-1.0/include -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/lib64/libffi/include  -I/usr/include/librsvg-2.0 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/lib64/libffi/include -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -pthread -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz   -I/usr/include/valgrind    -Wall -Wno-pointer-sign -g -O2 -MT oauth2.o -MD -MP -MF .deps/oauth2.Tpo -c -o oauth2.o oauth2.c
oauth2.c: In function 'oauth2_obtain_tokens':
oauth2.c:253:13: error: 'SockInfo' {aka 'struct _SockInfo'} has no member named 'gnutls_priority'
  253 |         sock->gnutls_priority = "NORMAL:!VERS-SSL3.0:!VERS-TLS1.0:!VERS-TLS1.1";
      |             ^~
oauth2.c:254:13: warning: implicit declaration of function 'ssl_init_socket' [-Wimplicit-function-declaration]
  254 |         if (ssl_init_socket(sock) == FALSE) {
      |             ^~~~~~~~~~~~~~~
oauth2.c: In function 'oauth2_use_refresh_token':
oauth2.c:405:13: error: 'SockInfo' {aka 'struct _SockInfo'} has no member named 'gnutls_priority'
  405 |         sock->gnutls_priority = "NORMAL:!VERS-SSL3.0:!VERS-TLS1.0:!VERS-TLS1.1";
      |             ^~
make[4]: *** [Makefile:1609: oauth2.o] Error 1


There is also a call to ssl_init_socket().

Overall I suppose oauth2 does not make a lot of sense without gnutls - so skip relevant code with --disable-gnutls ?


Downstream bug: https://bugs.gentoo.org/859583