Add a syntactic "Add Codable structs from JSON" code action

Sources/SourceKitLSP/CMakeLists.txt

@@ -23,6 +23,7 @@ target_sources(SourceKitLSP PRIVATE
   Swift/AdjustPositionToStartOfIdentifier.swift
   Swift/CodeActions/AddDocumentation.swift
   Swift/CodeActions/ConvertIntegerLiteral.swift
+  Swift/CodeActions/ConvertJSONToCodableStruct.swift
   Swift/CodeActions/PackageManifestEdits.swift
   Swift/CodeActions/SyntaxCodeActionProvider.swift
   Swift/CodeActions/SyntaxCodeActions.swift

Sources/SourceKitLSP/Swift/CodeActions/ConvertJSONToCodableStruct.swift

@@ -0,0 +1,389 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import LanguageServerProtocol
+import SwiftBasicFormat
+import SwiftRefactor
+import SwiftSyntax
+
+/// Convert JSON literals into corresponding Swift structs that conform to the
+/// `Codable` protocol.
+///
+/// ## Before
+///
+/// ```javascript
+/// {
+///   "name": "Produce",
+///   "shelves": [
+///     {
+///       "name": "Discount Produce",
+///       "product": {
+///         "name": "Banana",
+///         "points": 200,
+///         "description": "A banana that's perfectly ripe."
+///       }
+///     }
+///   ]
+/// }
+/// ```
+///
+/// ## After
+///
+/// ```swift
+/// struct JSONValue: Codable {
+///   var name: String
+///   var shelves: [Shelves]
+///
+///   struct Shelves: Codable {
+///     var name: String
+///     var product: Product
+///
+///     struct Product: Codable {
+///       var description: String
+///       var name: String
+///       var points: Double
+///     }
+///   }
+/// }
+/// ```
+@_spi(Testing)
+public struct ConvertJSONToCodableStruct: EditRefactoringProvider {
+  @_spi(Testing)
+  public static func textRefactor(
+    syntax: Syntax,
+    in context: Void
+  ) -> [SourceEdit] {
+    // Dig out a syntax node that looks like it might be JSON or have JSON
+    // in it.
+    guard let preflight = preflightRefactoring(syntax) else {
+      return []
+    }
+
+    // Dig out the text that we think might be JSON.
+    let text: String
+    switch preflight {
+    case let .closure(closure):
+      /// The outer structure of the JSON { ... } looks like a closure in the
+      /// syntax tree, albeit one with lots of ill-formed syntax in the body.
+      /// We're only going to look at the text of the closure to see if we
+      /// have JSON in there.
+      text = closure.trimmedDescription
+    case .stringLiteral(_, let literalText):
+      /// A string literal that could contain JSON within it.
+      text = literalText
+    }
+
+    // Try to process this as JSON.
+    guard
+      let object = try? JSONSerialization.jsonObject(with: text.data(using: .utf8)!),
+      let dictionary = object as? [String: Any]
+    else {
+      return []
+    }
+
+    // Create the top-level object.
+    let topLevelObject = JSONObject(dictionary: dictionary)
+
+    // Render the top-level object as a struct.
+    let indentation = BasicFormat.inferIndentation(of: syntax)
+    let format = BasicFormat(indentationWidth: indentation)
+    let decls = topLevelObject.asDeclSyntax(name: "JSONValue")
+      .formatted(using: format)
+
+    // Render the change into a set of source edits.
+    switch preflight {
+    case .closure(let closure):
+      // Closures are replaced entirely, since they were invalid code to
+      // start with.
+      return [
+        SourceEdit(range: closure.trimmedRange, replacement: decls.description)
+      ]
+    case .stringLiteral(let literal, _):
+      /// Leave the string literal in place (it might be there for testing
+      /// purposes), and put the newly-created structs afterward.
+      return [
+        SourceEdit(
+          range: literal.endPosition..<literal.endPosition,
+          replacement: "\n" + decls.description
+        )
+      ]
+    }
+  }
+}
+
+extension ConvertJSONToCodableStruct {
+  /// The result of preflighting a syntax node to try to find potential JSON
+  /// in it.
+  enum Preflight {
+    /// A closure, which is what a JSON dictionary looks like when pasted
+    /// into Swift.
+    case closure(ClosureExprSyntax)
+
+    /// A string literal that may contain JSON.
+    case stringLiteral(StringLiteralExprSyntax, String)
+  }
+
+  /// Look for either a closure or a string literal that might have JSON in it.
+  static func preflightRefactoring(_ syntax: Syntax) -> Preflight? {
+    // Preflight a closure.
+    //
+    // A blob of JSON dropped into a Swift source file will look like a
+    // closure due to the curly braces. The internals might be a syntactic
+    // disaster, but we don't actually care.
+    if let closure = syntax.as(ClosureExprSyntax.self) {
+      return .closure(closure)
+    }
+
+    // We found a string literal; its contents might be JSON.
+    if let stringLit = syntax.as(StringLiteralExprSyntax.self) {
+      // Look for an enclosing context and prefer that, because we might have
+      // a string literal that's inside a closure where the closure itself
+      // is the JSON.
+      if let parent = syntax.parent,
+        let enclosingPreflight = preflightRefactoring(parent)
+      {
+        return enclosingPreflight
+      }
+
+      guard let text = stringLit.representedLiteralValue else {
+        return nil
+      }
+
+      return .stringLiteral(stringLit, text)
+    }
+
+    // Look further up the syntax tree.
+    if let parent = syntax.parent {
+      return preflightRefactoring(parent)
+    }
+
+    return nil
+  }
+}
+
+extension ConvertJSONToCodableStruct: SyntaxRefactoringCodeActionProvider {
+  static var title = "Create Codable structs from JSON"
+}
+
+/// A JSON object, which is has a set of fields, each of which has the given
+/// type.
+fileprivate struct JSONObject {
+  /// The fields of the JSON object.
+  var fields: [String: JSONType] = [:]
+
+  /// Form a JSON object from its fields.
+  private init(fields: [String: JSONType]) {
+    self.fields = fields
+  }
+
+  /// Form a JSON object given a dictionary.
+  init(dictionary: [String: Any]) {
+    fields = dictionary.mapValues { JSONType(value: $0) }
+  }
+
+  /// Merge the fields of this JSON object with another JSON object to produce
+  /// a JSON object
+  func merging(with other: JSONObject) -> JSONObject {
+    // Collect the set of all keys from both JSON objects.
+    var allKeys: Set<String> = []
+    allKeys.formUnion(fields.keys)
+    allKeys.formUnion(other.fields.keys)
+
+    // Form a new JSON object containing the union of the fields
+    let newFields = allKeys.map { key in
+      let myValue = fields[key] ?? .null
+      let otherValue = other.fields[key] ?? .null
+      return (key, myValue.merging(with: otherValue))
+    }
+    return JSONObject(fields: [String: JSONType](uniqueKeysWithValues: newFields))
+  }
+
+  /// Render this JSON object into a struct.
+  func asDeclSyntax(name: String) -> DeclSyntax {
+    /// The list of fields in this object, sorted alphabetically.
+    let sortedFields = fields.sorted(by: { $0.key < $1.key })
+
+    // Collect the nested types
+    let nestedTypes: [(String, JSONObject)] = sortedFields.compactMap { (name, type) in
+      guard let object = type.innerObject else {
+        return nil
+      }
+
+      return (name.capitalized, object)
+    }
+
+    let members = MemberBlockItemListSyntax {
+      // Print the fields of this type.
+      for (fieldName, fieldType) in sortedFields {
+        MemberBlockItemSyntax(
+          leadingTrivia: .newline,
+          decl: "var \(raw: fieldName): \(fieldType.asTypeSyntax(name: fieldName))" as DeclSyntax
+        )
+      }
+
+      // Print any nested types.
+      for (typeName, object) in nestedTypes {
+        MemberBlockItemSyntax(
+          leadingTrivia: (typeName == nestedTypes.first?.0) ? .newlines(2) : .newline,
+          decl: object.asDeclSyntax(name: typeName)
+        )
+      }
+    }
+
+    return """
+      struct \(raw: name): Codable {
+        \(members.trimmed)
+      }
+      """
+  }
+}
+
+/// Describes the type of JSON data.
+fileprivate enum JSONType {
+  /// String data
+  case string
+
+  /// Numeric data
+  case number
+
+  /// Boolean data
+  case boolean
+
+  /// A "null", which implies optionality but without any underlying type
+  /// information.
+  case null
+
+  /// An array.
+  indirect case array(JSONType)
+
+  /// An object.
+  indirect case object(JSONObject)
+
+  /// A value that is optional, for example because it is missing or null in
+  /// other cases.
+  indirect case optional(JSONType)
+
+  /// Determine the type of a JSON value.
+  init(value: Any) {
+    switch value {
+    case let string as String:
+      if string == "true" || string == "false" {
+        self = .boolean
+      } else {
+        self = .string
+      }
+    case is NSNumber:
+      self = .number
+    case is NSArray:
+      let array = value as! [Any]
+
+      // Use null as a fallback for an empty array.
+      guard let firstValue = array.first else {
+        self = .array(.null)
+        return
+      }
+
+      // Merge the array elements.
+      let elementType: JSONType = array[1...].reduce(
+        JSONType(value: firstValue)
+      ) { (result, value) in
+        result.merging(with: JSONType(value: value))
+      }
+      self = .array(elementType)
+
+    case is NSNull:
+      self = .null
+    case is NSDictionary:
+      self = .object(JSONObject(dictionary: value as! [String: Any]))
+    default:
+      self = .string
+    }
+  }
+
+  /// Merge this JSON type with another JSON type, producing a new JSON type
+  /// that abstracts over the two.
+  func merging(with other: JSONType) -> JSONType {
+    switch (self, other) {
+    // Exact matches are easy.
+    case (.string, .string): return .string
+    case (.number, .number): return .number
+    case (.boolean, .boolean): return .boolean
+    case (.null, .null): return .null
+
+    case (.array(let inner), .array(.null)), (.array(.null), .array(let inner)):
+      // Merging an array with an array of null leaves the array.
+      return .array(inner)
+
+    case (.array(let inner), .null), (.null, .array(let inner)):
+      // Merging an array with a null just leaves an array.
+      return .array(inner)
+
+    case (.array(let left), .array(let right)):
+      // Merging two arrays merges the element types
+      return .array(left.merging(with: right))
+
+    case (.object(let left), .object(let right)):
+      // Merging two arrays merges the element types
+      return .object(left.merging(with: right))
+
+    // Merging a string with a Boolean means we misinterpreted "true" or
+    // "false" as Boolean when it was meant as a string.
+    case (.string, .boolean), (.boolean, .string): return .string
+
+    // Merging 'null' with an optional returns the optional.
+    case (.optional(let inner), .null), (.null, .optional(let inner)):
+      return .optional(inner)
+
+    // Merging 'null' with anything else makes it an optional.
+    case (let inner, .null), (.null, let inner):
+      return .optional(inner)
+
+    // Merging two optionals merges the underlying types and makes the
+    // result optional.
+    case (.optional(let left), .optional(let right)):
+      return .optional(left.merging(with: right))
+
+    // Merging an optional with anything else merges the underlying bits and
+    // makes them optional.
+    case (let outer, .optional(let inner)), (.optional(let inner), let outer):
+      return .optional(inner.merging(with: outer))
+
+    // Fall back to the null case when we don't know.
+    default:
+      return .null
+    }
+  }
+
+  /// Dig out the JSON inner object referenced by this type.
+  var innerObject: JSONObject? {
+    switch self {
+    case .string, .null, .number, .boolean: nil
+    case .optional(let inner): inner.innerObject
+    case .array(let inner): inner.innerObject
+    case .object(let object): object
+    }
+  }
+
+  /// Render this JSON type into type syntax.
+  func asTypeSyntax(name: String) -> TypeSyntax {
+    switch self {
+    case .string: "String"
+    case .number: "Double"
+    case .boolean: "Bool"
+    case .null: "Void"
+    case .optional(let inner): "\(inner.asTypeSyntax(name: name))?"
+    case .array(let inner): "[\(inner.asTypeSyntax(name: name))]"
+    case .object(_): "\(raw: name.capitalized)"
+    }
+  }
+}