How to Use 4XJGU4ZOUBY
 for Better Productivity Kuniwak - DeNA Co., Ltd. March 22, 2019 - try! Swift Tokyo 2019

2 Some code will be presented in the slides,
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About me

,VOJXBL • Software Engineer in Test • github.com/Kuniwak • qiita.com/Kuniwak • Favorites: testing/parsing • IDE: AppCode 4

What I want to share
 in these 5 minutes

6TJOH4XJGU4ZOUBY we can easily do Linting and Code Generation 6

What's SwiftSyntax?

4XJGU4ZOUBYis a library developed by Apple github.com/apple/swift-syntax 8

2 things Swift- Syntax can do

Readable/writable Data Convert Readable/Writable data into code Source Code Readable/writable Data 10 Source Code Convert code into Readable/Writable data

Readable/writable Data Convert Readable/Writable data into code Source Code Readable/writable Data 11 Source Code Convert code into Readable/Writable data

Convert code into Readable/Writable data if let self = self {} 12 This is an example code to explain

if let self = self {} If statement 13 This is an "if" statement Convert code into Readable/Writable data

if let self = self {} if let self = self {} If statement Body Condition 14 This if statements has
 2 components Convert code into Readable/Writable data

if let self = self {} if let self = self {} If statement Body Option binding condition 15 In this case, the Condition is
 the "Option binding condition" Convert code into Readable/Writable data

if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} 16 This option binding condition has
 2 components: "Identifier pattern" and
 "Identifier expression" Convert code into Readable/Writable data

if let self = self {} if let self = self {} if let self = self {} 17 If we look at the components,
 we can see we're traversing
 a tree through our code Convert code into Readable/Writable data

if let self = self {} if let self = self {} if let self = self {} 18 ෳจ If statement Body Identifier pattern Identifier expression Option binding condition Convert code into Readable/Writable data

19 if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} If statement Body Identifier pattern Identifier expression Option binding condition Convert code into Readable/Writable data This is cleed a "Syntax Tree"

Reading a Syntax Tree
 using SwiftSyntax

Reading a Syntax Tree using 4XJGU4ZOUBY if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} Let's read its name! 21

import SwiftSyntax let url = URL(fileURLWithPath: "example.swift") let source = try String(contentsOf: url) let syntax = try SyntaxParser.parse(source: source) Importing SwiftSyntax, creating the syntax tree that we need for reading the code and 22

if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} ifStmt Getting the if statement is
 bitty complicated. Thus it'll
 be explained later 23 Reading a Syntax Tree using 4XJGU4ZOUBY

if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} ifStmt .conditions[0] .condition 
 24 Reading a Syntax Tree using 4XJGU4ZOUBY

if let self = self {} if let self = self {} If statement Body Option binding condition Identifier
 expression Identifier
 pattern if let self = self {} "self" ifStmt .conditions[0] .condition .pattern
 .identifier .text 25 Reading a Syntax Tree using 4XJGU4ZOUBY

let name = ifStmt .conditions[0] .condition .pattern
 .identifier .text if name == "this" { print("Oops!") } For example, this is a Lint to
 check whether variable names
 follow your guideline Now, we can implement our Lint easily 26

import SwiftSyntax let url = URL(fileURLWithPath: "example.swift") let source = try String(contentsOf: url) let syntax = try SyntaxParser.parse(source: source)
 let stmts = Array(syntax.statements)
 guard let ifStmt = stmts.first?.item as? IfStmtSyntax else { print("If statement not found at the position.") return } You can see how to get the if statement using dump() the syntax tree How to get the If statement 27 Skipped in 
 presentation 


Readable/writable Data Convert Readable/Writable data into code Convert code into Readable/Writable data Source Code Readable/writable Data 28 Source Code DONE

Readable/writable Data Convert Readable/Writable data into code Convert code into Readable/Writable data Source Code Readable/writable Data 29 Source Code DONE

if let this = self {} Generating fixed code using 4XJGU4ZOUBY if let self = self {} 30

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) 31

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Use SwiftSyntax 32

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Get a syntax tree using SwiftSyntax 33

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Rewrite the syntax tree and print it 34

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) A class for rewriting syntax trees 35

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Use the override method to rewrite the node In this case, we want to rewrite the 9in "if let 9 = ..."
 (we can see the type of 9 by using dump) 36

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Rewrite the syntax tree if it says "if let this= ..." 37

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) Overwrite with "self" 38

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) 39

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) "if let self= self {}" 40 We got the fixed code!

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) "if let self= self {}" 41 But a space after "self" is missing...

import SwiftSyntax class RenameRewriter: SyntaxRewriter { override func visit(_ node: IdentifierPatternSyntax) -> PatternSyntax { if node.identifier.text == "this" { var modifiedNode = node let originalIdentifier = node.identifier modifiedNode.identifier = SyntaxFactory .makeIdentifier("self") .withTrailingTrivia(originalIdentifier.trailingTrivia) return modifiedNode } return node } } let syntax = try SyntaxParser.parse(source: String(contentsOf: url)) print(RenameRewriter().visit(syntax)) We can restore the space by using Trivias Skipped in 
 presentation 
 42

if let this = self {} if let self = self {} 43 DONE Generating fixed code using 4XJGU4ZOUBY

Readable/writable Data Convert Readable/Writable data into code Convert code into Readable/Writable data Source Code Readable/writable Data 44 Source Code DONE DONE

We implemented a Lint and Code Generator by using 4XJGU4ZOUBY! Conclusion 45