cmd/geth: print warning when whisper config is present in toml (#21544)

* cmd/geth: print warning when whisper config is present in toml

* Update cmd/geth/config.go
Co-authored-by: NMartin Holst Swende <martin@swende.se>

cmd/geth/config.go

@@ -73,8 +73,19 @@ type ethstatsConfig struct {
 	URL string `toml:",omitempty"`
 }
 
+// whisper has been deprecated, but clients out there might still have [Shh]
+// in their config, which will crash. Cut them some slack by keeping the
+// config, and displaying a message that those config switches are ineffectual.
+// To be removed circa Q1 2021 -- @gballet.
+type whisperDeprecatedConfig struct {
+	MaxMessageSize                        uint32  `toml:",omitempty"`
+	MinimumAcceptedPOW                    float64 `toml:",omitempty"`
+	RestrictConnectionBetweenLightClients bool    `toml:",omitempty"`
+}
+
 type gethConfig struct {
 	Eth      eth.Config
+	Shh      whisperDeprecatedConfig
 	Node     node.Config
 	Ethstats ethstatsConfig
 }
@@ -117,6 +128,10 @@ func makeConfigNode(ctx *cli.Context) (*node.Node, gethConfig) {
 		if err := loadConfig(file, &cfg); err != nil {
 			utils.Fatalf("%v", err)
 		}
+
+		if cfg.Shh != (whisperDeprecatedConfig{}) {
+			log.Warn("Deprecated whisper config detected. Whisper has been moved to github.com/ethereum/whisper")
+		}
 	}
 
 	// Apply flags.