Enforce error handling and checking type assertions (#5403)

* Enforce error handling and checking type assertions
* Reference issue #5404 in the TODO message
* doc description
* Merge branch 'master' into errcheck
* fix tests and address @nisdas feedbacK
* gaz
* fix docker image

tools/interop/convert-keys/main.go

@@ -57,7 +57,11 @@ func main() {
 	if err != nil {
 		log.Fatalf("Failed to create file at %s: %v", os.Args[2], err)
 	}
-	defer outFile.Close()
+	defer func() {
+		if err := outFile.Close(); err != nil {
+			panic(err)
+		}
+	}()
 	if err := keygen.SaveUnencryptedKeysToFile(outFile, out); err != nil {
 		log.Fatalf("Failed to save %v", err)
 	}

tools/interop/export-genesis/main.go

@@ -26,7 +26,11 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
-	defer d.Close()
+	defer func() {
+		if err := d.Close(); err != nil {
+			panic(err)
+		}
+	}()
 	gs, err := d.GenesisState(context.Background())
 	if err != nil {
 		panic(err)