fix(lwip): forward-declare struct dhcp before DHCP extra-option hook (IDFGH-17738)#18668
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When CONFIG_LWIP_HOOK_DHCP_EXTRA_OPTION_CUSTOM (or _DEFAULT) is enabled,
lwip_default_hooks.h declares
void lwip_dhcp_on_extra_option(struct dhcp *dhcp, ...);
while `struct dhcp` is only forward-declared further down, inside the
`#ifdef CONFIG_LWIP_IPV4` block. Any translation unit that includes the
header therefore declares `struct dhcp` inside the parameter list, which
GCC reports as:
error: 'struct dhcp' declared inside parameter list will not be
visible outside of this definition or declaration [-Werror]
The lwip component is built with -Werror and this diagnostic has no
individual -W flag to waive, so every project enabling the DHCP
extra-option hook fails to build. Reproduced on ESP-IDF v6.0.1 and
current master (GCC 13.2, xtensa-esp32s3).
Add a `struct dhcp;` forward declaration ahead of the prototype. A
pointer parameter only needs an incomplete type, so this is minimal and
sufficient; the redundant forward decl inside CONFIG_LWIP_IPV4 is left
untouched.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Problem
When
CONFIG_LWIP_HOOK_DHCP_EXTRA_OPTION_CUSTOM(or..._DEFAULT) isenabled,
components/lwip/port/include/lwip_default_hooks.hdeclares:but
struct dhcpis only forward-declared further down, inside the#ifdef CONFIG_LWIP_IPV4block — after this prototype. Everytranslation unit that includes the header therefore declares
struct dhcpinside the parameter list, which GCC reports as:
The lwip component is built with
-Werror, and this particular GCCdiagnostic has no individual
-Wflag, so it cannot be waived with-Wno-error=.... The result: any project that enables the DHCPextra-option hook fails to build.
Reproduction
master(GCC 13.2, xtensa-esp32s3)CONFIG_LWIP_HOOK_DHCP_EXTRA_OPTION_CUSTOM=ywith an app-providedlwip_dhcp_on_extra_option()implementationFix
Add a
struct dhcp;forward declaration ahead of the prototype. A pointerparameter only needs an incomplete type, so this is minimal and
sufficient. The redundant forward declaration inside
CONFIG_LWIP_IPV4is left untouched to keep the diff to a single added line.