AP_DAL: added standalone link test

useful to check for clean linking of EKF2/EKF3

Co-authored-by: Peter Barker <pbarker@barker.dropbear.id.au>

libraries/AP_DAL/examples/AP_DAL_Standalone/main.cpp

@@ -0,0 +1,67 @@
+//
+// Ensure that AP_NavEKF3 can be compiled when not linked to anything
+// except the DAL.
+//
+
+#include <AP_DAL/AP_DAL.h>
+
+#include <AP_NavEKF3/AP_NavEKF3.h>
+
+#include <AP_Logger/AP_Logger.h>
+
+void AP_Param::setup_object_defaults(void const*, AP_Param::GroupInfo const*) {}
+
+int AP_HAL::Util::vsnprintf(char*, unsigned long, char const*, va_list) { return -1; }
+
+void *nologger = nullptr;
+AP_Logger &AP::logger() {
+    return *((AP_Logger*)nologger);  // this is not usually a good idea...
+}
+void AP_Logger::WriteBlock(void const*, unsigned short) {}
+
+class AP_HAL_DAL_Standalone : public AP_HAL::HAL {
+public:
+    AP_HAL_DAL_Standalone() :
+        AP_HAL::HAL(
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr
+            ) {}
+    void run(int argc, char* const argv[], Callbacks* callbacks) const override {}
+    void setup() { }
+    void loop() { }
+};
+
+AP_HAL_DAL_Standalone _hal;
+const AP_HAL::HAL &hal = _hal;
+
+NavEKF2 navekf2;
+NavEKF3 navekf3;
+
+int main(int argc, const char *argv[])
+{
+    navekf2.InitialiseFilter();
+    navekf3.InitialiseFilter();
+    navekf2.UpdateFilter();
+    navekf3.UpdateFilter();
+    return navekf2.healthy() && navekf3.healthy()?0:1;
+}

libraries/AP_DAL/examples/AP_DAL_Standalone/wscript

@@ -0,0 +1,24 @@
+#!/usr/bin/env python
+# encoding: utf-8
+
+def build(bld):
+    bld.ap_stlib(
+        name='AP_DAL' + '_libs',
+        ap_vehicle='AP_DAL_Standalone',
+        ap_libraries=[
+            'AP_NavEKF2',
+            'AP_NavEKF3',
+            'AP_NavEKF',
+            'AP_Common',
+            'AP_Math',
+            'AP_DAL',
+            'AP_InternalError',
+            'AP_Declination',
+            'AP_RTC',
+        ],
+    )
+
+    bld.ap_program(
+        program_groups=['examples'],
+        use='AP_DAL_libs',
+    )