fix linter errors thrown by unconvert, goconst, and nakedret (#3960)

* Remove unnecessary type conversions

* Consolidate repeated strings into consts

* Clothe return statements

* Update blockchain/v1/reactor_fsm_test.go

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

This PR repairs linter errors seen when running the following commands:
golangci-lint run --no-config --disable-all=true --enable=unconvert
golangci-lint run --no-config --disable-all=true --enable=goconst
golangci-lint run --no-config --disable-all=true --enable=nakedret

Contributes to #3262

rpc/client/rpc_test.go

@@ -559,7 +559,7 @@ func makeEvidences(t *testing.T, val *privval.FilePV, chainID string) (ev types.
 	// exactly same vote
 	vote2 = deepcpVote(vote)
 	fakes[41] = newEvidence(t, val, vote, vote2, chainID)
-	return
+	return ev, fakes
 }
 
 func TestBroadcastEvidenceDuplicateVote(t *testing.T) {

rpc/core/tx.go

@@ -106,7 +106,7 @@ func Tx(ctx *rpctypes.Context, hash []byte, prove bool) (*ctypes.ResultTx, error
 	return &ctypes.ResultTx{
 		Hash:     hash,
 		Height:   height,
-		Index:    uint32(index),
+		Index:    index,
 		TxResult: r.Result,
 		Tx:       r.Tx,
 		Proof:    proof,

rpc/lib/rpc_test.go

@@ -33,6 +33,8 @@ const (
 	unixAddr   = "unix://" + unixSocket
 
 	websocketEndpoint = "/websocket/endpoint"
+
+	testVal = "acbd"
 )
 
 type ResultEcho struct {
@@ -189,7 +191,7 @@ func echoDataBytesViaHTTP(cl client.HTTPClient, bytes cmn.HexBytes) (cmn.HexByte
 }
 
 func testWithHTTPClient(t *testing.T, cl client.HTTPClient) {
-	val := "acbd"
+	val := testVal
 	got, err := echoViaHTTP(cl, val)
 	require.Nil(t, err)
 	assert.Equal(t, got, val)
@@ -255,7 +257,7 @@ func echoBytesViaWS(cl *client.WSClient, bytes []byte) ([]byte, error) {
 }
 
 func testWithWSClient(t *testing.T, cl *client.WSClient) {
-	val := "acbd"
+	val := testVal
 	got, err := echoViaWS(cl, val)
 	require.Nil(t, err)
 	assert.Equal(t, got, val)
@@ -314,7 +316,7 @@ func TestWSNewWSRPCFunc(t *testing.T) {
 	require.Nil(t, err)
 	defer cl.Stop()
 
-	val := "acbd"
+	val := testVal
 	params := map[string]interface{}{
 		"arg": val,
 	}
@@ -339,7 +341,7 @@ func TestWSHandlesArrayParams(t *testing.T) {
 	require.Nil(t, err)
 	defer cl.Stop()
 
-	val := "acbd"
+	val := testVal
 	params := []interface{}{val}
 	err = cl.CallWithArrayParams(context.Background(), "echo_ws", params)
 	require.Nil(t, err)

rpc/lib/server/handlers.go

@@ -376,9 +376,9 @@ func _nonJSONStringToArg(cdc *amino.Codec, rt reflect.Type, arg string) (reflect
 		rv, err := jsonStringToArg(cdc, rt, qarg)
 		if err != nil {
 			return rv, err, false
-		} else {
-			return rv, nil, true
 		}
+
+		return rv, nil, true
 	}
 
 	if isHexString {
@@ -396,7 +396,7 @@ func _nonJSONStringToArg(cdc *amino.Codec, rt reflect.Type, arg string) (reflect
 		if rt.Kind() == reflect.String {
 			return reflect.ValueOf(string(value)), nil, true
 		}
-		return reflect.ValueOf([]byte(value)), nil, true
+		return reflect.ValueOf(value), nil, true
 	}
 
 	if isQuotedString && expectingByteSlice {

rpc/lib/types/types_test.go

@@ -39,17 +39,17 @@ func TestResponses(t *testing.T) {
 		a := NewRPCSuccessResponse(cdc, jsonid, &SampleResult{"hello"})
 		b, _ := json.Marshal(a)
 		s := fmt.Sprintf(`{"jsonrpc":"2.0","id":%v,"result":{"Value":"hello"}}`, tt.expected)
-		assert.Equal(string(s), string(b))
+		assert.Equal(s, string(b))
 
 		d := RPCParseError(jsonid, errors.New("Hello world"))
 		e, _ := json.Marshal(d)
 		f := fmt.Sprintf(`{"jsonrpc":"2.0","id":%v,"error":{"code":-32700,"message":"Parse error. Invalid JSON","data":"Hello world"}}`, tt.expected)
-		assert.Equal(string(f), string(e))
+		assert.Equal(f, string(e))
 
 		g := RPCMethodNotFoundError(jsonid)
 		h, _ := json.Marshal(g)
 		i := fmt.Sprintf(`{"jsonrpc":"2.0","id":%v,"error":{"code":-32601,"message":"Method not found"}}`, tt.expected)
-		assert.Equal(string(h), string(i))
+		assert.Equal(string(h), i)
 	}
 }