cleanup: remove redundant error plumbing (#6778)

This is a mostly-automated fixup using Comby (https://comby.dev) to remove 
lexically-obvious redundant error checks. No functional changes are intended.

To reproduce the core change:

    # Collapse redundant error check conditionals
    % comby -in-place 'if err != nil {
       return err
    }
    return nil' 'return err' .go

    # Fold out unnecessary error temporaries
    % comby -in-place ':[spc~^\s*]err :[~:?]= :[any]
       return err' ':[spc]return :[any]' .go

Fixes #6479 and related cases.

abci/types/messages.go

@@ -15,11 +15,7 @@ const (
 func WriteMessage(msg proto.Message, w io.Writer) error {
 	protoWriter := protoio.NewDelimitedWriter(w)
 	_, err := protoWriter.WriteMsg(msg)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return err
 }
 
 // ReadMessage reads a varint length-delimited protobuf message.

privval/signer_listener_endpoint.go

@@ -142,12 +142,7 @@ func (sl *SignerListenerEndpoint) ensureConnection(maxWait time.Duration) error
 	// block until connected or timeout
 	sl.Logger.Info("SignerListener: Blocking for connection")
 	sl.triggerConnect()
-	err := sl.WaitConnection(sl.connectionAvailableCh, maxWait)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return sl.WaitConnection(sl.connectionAvailableCh, maxWait)
 }
 
 func (sl *SignerListenerEndpoint) acceptNewConnection() (net.Conn, error) {

state/indexer/sink/psql/psql_test.go

@@ -255,12 +255,7 @@ func verifyTimeStamp(tb string) error {
 
 	if rows.Next() {
 		var ts string
-		err = rows.Scan(&ts)
-		if err != nil {
-			return err
-		}
-
-		return nil
+		return rows.Scan(&ts)
 	}
 
 	return errors.New("no result")

state/store.go

@@ -661,10 +661,5 @@ func (store dbStore) saveConsensusParamsInfo(
 		return err
 	}
 
-	err = batch.Set(consensusParamsKey(nextHeight), bz)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return batch.Set(consensusParamsKey(nextHeight), bz)
 }

test/e2e/runner/cleanup.go

@@ -15,11 +15,7 @@ func Cleanup(testnet *e2e.Testnet) error {
 	if err != nil {
 		return err
 	}
-	err = cleanupDir(testnet.Dir)
-	if err != nil {
-		return err
-	}
-	return nil
+	return cleanupDir(testnet.Dir)
 }
 
 // cleanupDocker removes all E2E resources (with label e2e=True), regardless
@@ -37,13 +33,8 @@ func cleanupDocker() error {
 		return err
 	}
 
-	err = exec("bash", "-c", fmt.Sprintf(
+	return exec("bash", "-c", fmt.Sprintf(
 		"docker network ls -q --filter label=e2e | xargs %v docker network rm", xargsR))
-	if err != nil {
-		return err
-	}
-
-	return nil
 }
 
 // cleanupDir cleans up a testnet directory
@@ -74,10 +65,5 @@ func cleanupDir(dir string) error {
 		return err
 	}
 
-	err = os.RemoveAll(dir)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return os.RemoveAll(dir)
 }

test/e2e/runner/wait.go

@@ -21,10 +21,7 @@ func Wait(testnet *e2e.Testnet, blocks int64) error {
 func WaitUntil(testnet *e2e.Testnet, height int64) error {
 	logger.Info(fmt.Sprintf("Waiting for all nodes to reach height %v...", height))
 	_, err := waitForAllNodes(testnet, height, waitingTime(len(testnet.Nodes)))
-	if err != nil {
-		return err
-	}
-	return nil
+	return err
 }
 
 // waitingTime estimates how long it should take for a node to reach the height.

test/fuzz/rpc/jsonrpc/server/handler.go

@@ -59,6 +59,5 @@ func Fuzz(data []byte) int {
 
 func outputJSONIsSlice(input []byte) bool {
 	slice := []interface{}{}
-	err := json.Unmarshal(input, &slice)
-	return err == nil
+	return json.Unmarshal(input, &slice) == nil
 }

types/node_key.go

@@ -33,11 +33,7 @@ func (nodeKey NodeKey) SaveAs(filePath string) error {
 	if err != nil {
 		return err
 	}
-	err = ioutil.WriteFile(filePath, jsonBytes, 0600)
-	if err != nil {
-		return err
-	}
-	return nil
+	return ioutil.WriteFile(filePath, jsonBytes, 0600)
 }
 
 // LoadOrGenNodeKey attempts to load the NodeKey from the given filePath. If