Merge bitcoin/bitcoin#31916: init: Handle dropped UPnP support more gracefully

44041ae init: Handle dropped UPnP support more gracefully (laanwj)

Pull request description:

  Closes #843.

  In that issue it was brought up that users likely don't care what kind of port forwarding is used, and that the setting is opportunistic anyway, so instead of showing an extensive warning, we can simply "upgrade" from UPNP to NAT-PMP+PCP.

  - Change the logic for removed runtime setting `-upnp` to set `-natpmp` instead, and log a message.

  - Also remove any lingering `upnp` from `settings.json` and replace it with `natpmp`, when it makes sense (this is important so that the UI shows the right values in the settings):

  ```json
  {
      "upnp": true
  }
  ```
  becomes
  ```json
  {
      "natpmp": true
  }
  ```

  and

  ```json
  {
      "upnp": false
  }
  ```
  becomes
  ```json
  {
      "natpmp": false
  }
  ```

ACKs for top commit:
  darosior:
    tACK 44041ae
  davidgumberg:
    lightly reviewed code, tested ACK bitcoin/bitcoin@44041ae
  achow101:
    ACK 44041ae
  ryanofsky:
    Code review ACK 44041ae. Code changes look good. Could potentially add test coverage for this, though I don't think it is too important.
  hodlinator:
    cr-ACK 44041ae

Tree-SHA512: ca822f7160529e59973bab6a7cc31753ffa3caaa806887b5073b42c4ae5c918a5ea2cf93c666e5125ea70d10c6954709a535a264b04c2fd4cf916b3c59ab9964

Author: achow101

src/init.cpp

@@ -793,6 +793,32 @@ void InitParameterInteraction(ArgsManager& args)
             LogInfo("parameter interaction: -onlynet excludes IPv4 and IPv6 -> setting -dnsseed=0\n");
         }
     }
+
+    // If settings.json contains a "upnp" option, migrate it to use "natpmp" instead
+    bool settings_changed{false}; // Whether settings.json file needs to be rewritten
+    args.LockSettings([&](common::Settings& settings) {
+        if (auto* upnp{common::FindKey(settings.rw_settings, "upnp")}) {
+            if (common::FindKey(settings.rw_settings, "natpmp") == nullptr) {
+                LogWarning(R"(Adding "natpmp": %s to settings.json to replace obsolete "upnp" setting)", upnp->write());
+                settings.rw_settings["natpmp"] = *upnp;
+            }
+            LogWarning(R"(Removing obsolete "upnp" setting from settings.json)");
+            settings.rw_settings.erase("upnp");
+            settings_changed = true;
+        }
+    });
+    if (settings_changed) args.WriteSettingsFile();
+
+    // We dropped UPnP support but kept the arg as hidden for now to display a friendlier error to user who has the
+    // option in their config, and migrate the setting to -natpmp.
+    if (const auto arg{args.GetBoolArg("-upnp")}) {
+        std::string message;
+        if (args.SoftSetBoolArg("-natpmp", *arg)) {
+            message = strprintf(" Substituting '-natpmp=%s'.", *arg);
+        }
+        LogWarning("Option '-upnp=%s' is given but UPnP support was dropped in version 29.0.%s",
+                *arg, message);
+    }
 }
 
 /**
@@ -874,12 +900,6 @@ bool AppInitParameterInteraction(const ArgsManager& args)
 
     // also see: InitParameterInteraction()
 
-    // We drop UPnP support but kept the arg as hidden for now to display a friendlier error to user who have the
-    // option in their config. TODO: remove (here and above) for version 30.0.
-    if (args.IsArgSet("-upnp")) {
-        InitWarning(_("Option '-upnp' is set but UPnP support was dropped in version 29.0. Consider using '-natpmp' instead."));
-    }
-
     // Error if network-specific options (-addnode, -connect, etc) are
     // specified in default section of config file, but not overridden
     // on the command line or in this chain's section of the config file.