lib: Add MODULE_CONTEXT_REQUIRE

This will panic instead of return NULL. Should satisfy static
analyzers when used.

src/lib/module-context.h

@@ -50,6 +50,15 @@
 		module_get_context_id(&(id_ctx).id)) + \
 	 OBJ_REGISTER_COMPATIBLE(obj, id_ctx)))
 
+/* Will crash if context is missing. This is mainly used to simplify code and
+   keep static analyzers happy. This syntax discards result of i_panic and
+   returns NULL instead to keep compilers happy. */
+#define MODULE_CONTEXT_REQUIRE(obj, id_ctx) \
+	(module_get_context_id(&(id_ctx).id) < array_count(&(obj)->module_contexts) ? \
+	 (*((void **)array_idx_modifiable(&(obj)->module_contexts,      \
+		module_get_context_id(&(id_ctx).id)) + \
+	    OBJ_REGISTER_COMPATIBLE(obj, id_ctx))) : (i_panic("Module context " #id_ctx " missing"), NULL))
+
 #ifdef HAVE_TYPEOF
 #  define MODULE_CONTEXT_DEFINE(_name, _reg) \
 	struct _name { \