Add new example

Author: flashspys

Examples/MigrateToNewIfLetSyntax.swift

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+import Foundation
+import SwiftSyntax
+import SwiftParser
+
+/// MigrateToNewIfLetSyntax will visit each if statement in the Syntax tree, and
+/// checks if the there is an if condition which is of the pre Swift 5.7 "if-let-style"
+/// and rewrites it to the new one
+///
+/// For example will it turn:
+/// ```
+/// if let foo = foo {
+///   ...
+/// }
+/// ```
+/// into:
+/// ```
+/// if let foo {
+///   ...
+/// }
+class MigrateToNewIfLetSyntax: SyntaxRewriter {
+  // Visit over all IfStmtSyntax nodes
+  override func visit(_ node: IfStmtSyntax) -> StmtSyntax {
+    // For each node, visit all conditions in this node
+    let newConditions = node.conditions.enumerated().map { (index, condition) in
+      var conditionCopy = condition
+      // check if the condition is a OptionalBindingConditionSyntax...
+      if var binding = condition.condition.as(OptionalBindingConditionSyntax.self),
+         // ...and has an initializer
+         let initializer = binding.initializer,
+         // and the name of the variable pattern and the initializer is the same, ignoring any whitespace
+         binding.pattern.withoutTrivia().description == initializer.value.withoutTrivia().description {
+        // Remove the initializer
+        binding.initializer = nil
+        // And remove whitespace (the space before the comma) in if statements with multiple conditions
+        if index != node.conditions.count - 1 {
+          binding.pattern = binding.pattern.withoutTrailingTrivia()
+        }
+        conditionCopy.condition = Syntax(binding)
+      }
+      return conditionCopy
+    }
+    return StmtSyntax(node.withConditions(ConditionElementListSyntax(newConditions)))
+  }
+  
+  /// Utility function to migrate all swift files in a folder and its subfolders
+  static func migrate(folderPath: String) {
+    for case let fileURL as String in FileManager.default.enumerator(atPath: folderPath)! {
+      if fileURL.hasSuffix("swift") {
+        print("Rewriting", fileURL)
+        let fullPath = folderPath + "/" + fileURL
+        let tree = try! Parser.parse(source: String(data: FileManager.default.contents(atPath: fullPath)!, encoding: .utf8 )!)
+        let newTree = MigrateToNewIfLetSyntax().visit(tree)
+        try! newTree.description.write(toFile: fullPath, atomically: true, encoding: .utf8)
+      }
+    }
+  }
+}
+
+MigrateToNewIfLetSyntax.migrate(folderPath: "/path/to/folder")