settings: add auto-generated warning msg for editing the file manually

Hopefully, refraining users from modifying the file unless they are
certain about the potential consequences.

Co-authored-by: Ryan Ofsky <ryan@ofsky.org>

Author: furszy

src/common/settings.cpp

@@ -4,6 +4,10 @@
 
 #include <common/settings.h>
 
+#if defined(HAVE_CONFIG_H)
+#include <config/bitcoin-config.h>
+#endif
+
 #include <tinyformat.h>
 #include <univalue.h>
 #include <util/fs.h>
@@ -116,6 +120,13 @@ bool WriteSettings(const fs::path& path,
     std::vector<std::string>& errors)
 {
     SettingsValue out(SettingsValue::VOBJ);
+    // Add auto-generated warning comment only if it does not exist
+    if (!values.contains("_warning_")) {
+        out.pushKV("_warning_", strprintf("This file is automatically generated and updated by %s. Please do not edit this file while the node "
+                                          "is running, as any changes might be ignored or overwritten.",
+                                          PACKAGE_NAME));
+    }
+    // Push settings values
     for (const auto& value : values) {
         out.pushKVEnd(value.first, value.second);
     }

src/qt/test/optiontests.cpp

@@ -61,7 +61,11 @@ void OptionTests::migrateSettings()
     QVERIFY(!settings.contains("addrSeparateProxyTor"));
 
     std::ifstream file(gArgs.GetDataDirNet() / "settings.json");
+    std::string default_warning = strprintf("This file is automatically generated and updated by %s. Please do not edit this file while the node "
+                                            "is running, as any changes might be ignored or overwritten.",
+                                            PACKAGE_NAME);
     QCOMPARE(std::string(std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>()).c_str(), "{\n"
+        "    \"_warning_\": \""+ default_warning+"\",\n"
         "    \"dbcache\": \"600\",\n"
         "    \"listen\": false,\n"
         "    \"onion\": \"onion:234\",\n"

test/functional/feature_settings.py

@@ -23,10 +23,11 @@ def run_test(self):
         settings = node.chain_path / "settings.json"
         conf = node.datadir_path / "bitcoin.conf"
 
-        # Assert empty settings file was created
+        # Assert default settings file was created
         self.stop_node(0)
+        default_settings = {"_warning_": "This file is automatically generated and updated by Bitcoin Core. Please do not edit this file while the node is running, as any changes might be ignored or overwritten."}
         with settings.open() as fp:
-            assert_equal(json.load(fp), {})
+            assert_equal(json.load(fp), default_settings)
 
         # Assert settings are parsed and logged
         with settings.open("w") as fp:
@@ -48,7 +49,7 @@ def run_test(self):
 
         # Assert settings are unchanged after shutdown
         with settings.open() as fp:
-            assert_equal(json.load(fp), {"string": "string", "num": 5, "bool": True, "null": None, "list": [6, 7]})
+            assert_equal(json.load(fp), {**default_settings, **{"string": "string", "num": 5, "bool": True, "null": None, "list": [6, 7]}})
 
         # Test invalid json
         with settings.open("w") as fp: