Release builds fail to compile due to unused variable

[electricbrass]

When trying to build libwebsockets, it fails in lib/core/context.c due to an unused variable. This seems to only occur on release builds. On debug builds, there is no issue.

[cmake] /home/mia/source/odamex/libraries/libwebsockets/lib/core/context.c:1765:20: error: ‘cname’ defined but not used [-Werror=unused-variable]
[cmake]  1765 | static const char *cname[] = { "Unknown", "OK", "Captive", "No internet" };
[cmake]       |                    ^~~~~

In my case LWS_WITH_SYS_STATE is disabled, as is LWS_WITH_NO_LOGS.

libwebsockets/lib/core/context.c

Lines 1764 to 1766 in 85c6f79

	#if (defined(LWS_WITH_SYS_STATE) && defined(LWS_WITH_SYS_SMD)) || !defined(LWS_WITH_NO_LOGS)
	static const char *cname[] = { "Unknown", "OK", "Captive", "No internet" };
	#endif

As far as I can tell, that means cname is defined, and is used only a few lines later:

libwebsockets/lib/core/context.c

Lines 1774 to 1776 in 85c6f79

	#if !defined(LWS_WITH_NO_LOGS)
	lwsl_cx_info(cx, "setting CPD result %s", cname[result]);
	#endif

So I don't understand why there would be an error for it being unused.

I am using v4.5.2

[electricbrass]

libwebsockets/include/libwebsockets/lws-logs.h

Lines 371 to 375 in d8c745e

	#if (_LWS_ENABLED_LOGS & LLL_INFO)
	#define lwsl_cx_info(_c, ...) lwsl_cx(_c, LLL_INFO, __VA_ARGS__)
	#else
	#define lwsl_cx_info(_c, ...) do {} while(0)
	#endif

libwebsockets/include/libwebsockets/lws-logs.h

Lines 218 to 233 in d8c745e

	#if defined(_DEBUG)
	/*
	* In DEBUG build, select all logs unless NO_LOGS
	*/
	#if defined(LWS_WITH_NO_LOGS)
	#define _LWS_LINIT (LLL_ERR | LLL_USER)
	#else
	#define _LWS_LINIT ((1 << LLL_COUNT) - 1)
	#endif
	#else /* not _DEBUG */
	#if defined(LWS_WITH_NO_LOGS)
	#define _LWS_LINIT (LLL_ERR | LLL_USER)
	#else
	#define _LWS_LINIT (LLL_ERR | LLL_USER | LLL_WARN | LLL_NOTICE)
	#endif
	#endif /* _DEBUG */

Here we go, it looks like on a release build (_LWS_ENABLED_LOGS & LLL_INFO) is false, and so this lwsl_cx_info gets turned into an empty do-while that doesn't use cname.

[lws-team]

The difficulty is coming because in release mode, INFO level debug messages are not built... so there is effectively no usage of cname[] even though NO_LOGS is not set. The fix below solves it by checking if INFO level debug messages are buit or not

diff --git a/lib/core/context.c b/lib/core/context.c
index 299106b5..07278507 100644
--- a/lib/core/context.c
+++ b/lib/core/context.c
@@ -1795,7 +1795,7 @@ lws_system_cpd_start_defer(struct lws_context *cx, lws_usec_t defer_us)
                         lws_system_deferred_cb, defer_us);
 }
 
-#if (defined(LWS_WITH_SYS_STATE) && defined(LWS_WITH_SYS_SMD)) || !defined(LWS_WITH_NO_LOGS)
+#if (defined(LWS_WITH_SYS_STATE) && defined(LWS_WITH_SYS_SMD)) || (_LWS_ENABLED_LOGS & LLL_INFO)
 static const char *cname[] = { "Unknown", "OK", "Captive", "No internet" };
 #endif
 
@@ -1805,7 +1805,7 @@ lws_system_cpd_set(struct lws_context *cx, lws_cpd_result_t result)
        if (cx->captive_portal_detect != LWS_CPD_UNKNOWN)
                return;
 
-#if !defined(LWS_WITH_NO_LOGS)
+#if (_LWS_ENABLED_LOGS & LLL_INFO) 
        lwsl_cx_info(cx, "setting CPD result %s", cname[result]);
 #endif
 

[electricbrass]

Just tested with:

diff --git a/lib/core/context.c b/lib/core/context.c
index 64028b0f..0076eb62 100644
--- a/lib/core/context.c
+++ b/lib/core/context.c
@@ -1761,7 +1761,7 @@ lws_system_cpd_start_defer(struct lws_context *cx, lws_usec_t defer_us)
                         lws_system_deferred_cb, defer_us);
 }
 
-#if (defined(LWS_WITH_SYS_STATE) && defined(LWS_WITH_SYS_SMD)) || !defined(LWS_WITH_NO_LOGS)
+#if (defined(LWS_WITH_SYS_STATE) && defined(LWS_WITH_SYS_SMD)) || (_LWS_ENABLED_LOGS & LLL_INFO)
 static const char *cname[] = { "Unknown", "OK", "Captive", "No internet" };
 #endif
 
@@ -1771,9 +1771,7 @@ lws_system_cpd_set(struct lws_context *cx, lws_cpd_result_t result)
        if (cx->captive_portal_detect != LWS_CPD_UNKNOWN)
                return;
 
-#if !defined(LWS_WITH_NO_LOGS)
        lwsl_cx_info(cx, "setting CPD result %s", cname[result]);
-#endif
 
        cx->captive_portal_detect = (uint8_t)result;

I got rid of the #if around the the lwsl_cx_info since that's already a macro that's that only does anything when (_LWS_ENABLED_LOGS & LLL_INFO)
Didn't encounter any issues :)
Thanks

[electricbrass]

No rush, but just wondering if this will be making its way to main or v4.5-stable any time soon since the fix is already known now.

[lws-team]

There's a big backport of fixes found on main to v4.5-stable yesterday as "4.5.3", I will tag it out later.