Addon-config: don’t overwrite autosaved props

Fix for: https://sourceforge.net/p/flightgear/codetickets/2059/

When copying addon-config into the main property tree, skip props
which already exist and which are marked ARCHIVE, on the assumption
they came from autosave.xml.

src/Add-ons/AddonManager.cxx

@@ -96,13 +96,33 @@ AddonManager::loadConfigFileIfExists(const SGPath& configFile)
     return;
   }
 
+  SGPropertyNode_ptr configProps(new SGPropertyNode);
   try {
-    readProperties(configFile, globals->get_props());
+    readProperties(configFile, configProps);
   } catch (const sg_exception &e) {
     throw errors::error_loading_config_file(
       "unable to load add-on config file '" + configFile.utf8Str() + "': " +
       e.getFormattedMessage());
   }
+  
+  // bug https://sourceforge.net/p/flightgear/codetickets/2059/
+  // since we're loading this after autosave.xml is loaded, the defaults
+  // always take precedence. To fix this, only copy a value from the
+  // addon-config if it's not makred as ARCHIVE. (We assume ARCHIVE props
+  // came from autosave.xml)
+  copyPropertiesIf(configProps, globals->get_props(), [](const SGPropertyNode* src) {
+    if (src->nChildren() > 0)
+      return true;
+    
+    // find the correspnding destination node
+    auto dstNode = globals->get_props()->getNode(src->getPath());
+    if (!dstNode)
+      return true; // easy, just copy it
+    
+    // copy if it's NOT marked archive. In other words, we can replace
+    // values from defaults, but not autosave
+    return dstNode->getAttribute(SGPropertyNode::ARCHIVE) == false;
+  });
 
   SG_LOG(SG_GENERAL, SG_INFO,
          "Loaded add-on config file: '" << configFile.utf8Str() + "'");

test_suite/simgear_tests/props/test_props.cxx

@@ -20,6 +20,7 @@
 
 #include "test_props.hxx"
 
+#include <simgear/props/props_io.hxx>
 
 // Set up function for each test.
 void SimgearPropsTests::setUp()
@@ -50,3 +51,31 @@ void SimgearPropsTests::testAliasLeak()
     alias = tree->getNode("test-alias", true);
     alias->alias("test-node");
 }
+
+void SimgearPropsTests::testPropsCopyIf()
+{
+// dummy property tree structure
+    tree->setIntValue("a/a/a", 42);
+    tree->setStringValue("a/a/b", "foo");
+    tree->setIntValue("a/a/c[2]", 99);
+    tree->setIntValue("a/a/d", 1);
+    tree->setIntValue("a/b/a[0]", 50);
+    tree->setIntValue("a/b/a[1]", 100);
+    tree->setStringValue("a/b/b", "foo");
+
+    SGPropertyNode_ptr destA(new SGPropertyNode);
+
+    copyPropertiesIf(tree, destA, [](const SGPropertyNode* src) {
+        // always copy non-leaf nodes
+        if (src->nChildren() > 0) 
+            return true;
+
+        return (src->getType() == simgear::props::INT) &&
+            src->getIntValue() > 50;
+    });
+
+    CPPUNIT_ASSERT_EQUAL(1, destA->getNode("a/a")->nChildren()); // only 99
+    CPPUNIT_ASSERT_EQUAL(99, destA->getIntValue("a/a/c[2]"));
+    CPPUNIT_ASSERT_EQUAL(1, destA->getNode("a/b")->nChildren()); // only 100
+    CPPUNIT_ASSERT_EQUAL(100, destA->getIntValue("a/b/a[1]"));
+}

test_suite/simgear_tests/props/test_props.hxx

@@ -34,6 +34,7 @@ class SimgearPropsTests : public CppUnit::TestFixture
     // Set up the test suite.
     CPPUNIT_TEST_SUITE(SimgearPropsTests);
     CPPUNIT_TEST(testAliasLeak);
+    CPPUNIT_TEST(testPropsCopyIf);
     CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -45,7 +46,7 @@ public:
 
     // The tests.
     void testAliasLeak();
-
+    void testPropsCopyIf();
 private:
     // A property tree.
     SGPropertyNode *tree;