Merge #16115: On bitcoind startup, write config args to debug.log

b951b0973cfd4e0db4607a00d434a04afb0d6199 on startup, write config options to debug.log (Larry Ruane)

Pull request description:

  When a developer is examining `debug.log` after something goes wrong, it's often useful to know the exact options the failing instance of `bitcoind` was started with. Sometimes the `debug.log` file is all that's available for the analysis. This PR logs the `bitcoin.conf` entries and command-line arguments to `debug.log` on startup.

ACKs for top commit:
  MarcoFalke:
    ACK b951b0973cfd4e0db4607a00d434a04afb0d6199 🐪
  jonatack:
    ACK b951b0973c reviewed diff, re-code review, built, ran tests, launched bitcoind and reviewed debug log output, verified value of  `str` debug log in the added unit test.

Tree-SHA512: bbca4fb3d49f99261758302bde0b8b67300ccc72e7380b01f1f66a146ae8a008a045df0ca5ca9664caff034d0ee38ea7ef38a50f38374525608c07ba52790358

1 files changed, 15 insertions, 0 deletions

diff --git a/src/util/system.h b/src/util/system.h
index 473019bbed..bb69181de9 100644
--- a/src/util/system.h
+++ b/src/util/system.h
@@ -145,6 +145,8 @@ public:
          * between mainnet and regtest/testnet won't cause problems due to these
          * parameters by accident. */
         NETWORK_ONLY = 0x200,
+        // This argument's value is sensitive (such as a password).
+        SENSITIVE = 0x400,
     };
 
 protected:
@@ -318,6 +320,19 @@ public:
      * Return nullopt for unknown arg.
      */
     Optional<unsigned int> GetArgFlags(const std::string& name) const;
+
+    /**
+     * Log the config file options and the command line arguments,
+     * useful for troubleshooting.
+     */
+    void LogArgs() const;
+
+private:
+    // Helper function for LogArgs().
+    void logArgsPrefix(
+        const std::string& prefix,
+        const std::string& section,
+        const std::map<std::string, std::vector<util::SettingsValue>>& args) const;
 };
 
 extern ArgsManager gArgs;