Merge pull request swiftlang#78 from akyrtzi/reversed-collection

[SyntaxCollections] Add a reversed `Sequence` for `SyntaxCollection`s

Author: akyrtzi

Sources/SwiftSyntax/SyntaxChildren.swift

@@ -54,10 +54,14 @@ struct RawSyntaxChildren: Sequence {
   }
 }
 
+protocol AbsoluteRawSyntaxIteratorProtocol:
+  IteratorProtocol where Element == AbsoluteRawSyntax {
+}
+
 /// Sequence of `AbsoluteRawSyntax` formed from all the `present` layout
 /// children nodes of a raw node.
 struct PresentRawSyntaxChildren: Sequence {
-  struct Iterator: IteratorProtocol {
+  struct Iterator: AbsoluteRawSyntaxIteratorProtocol {
     var iterator: RawSyntaxChildren.Iterator
 
     init(parent: AbsoluteRawSyntax) {
@@ -98,7 +102,7 @@ struct PresentRawSyntaxChildren: Sequence {
 
 /// Reversed Sequence of `PresentRawSyntaxChildren`.
 struct ReversedPresentRawSyntaxChildren: Sequence {
-  struct Iterator: IteratorProtocol {
+  struct Iterator: AbsoluteRawSyntaxIteratorProtocol {
     let parent: RawSyntax
     var previousChildInfo: AbsoluteSyntaxInfo
 

Sources/SwiftSyntax/SyntaxCollections.swift.gyb

@@ -157,6 +157,22 @@ public struct ${node.name}: _SyntaxBase, Hashable, SyntaxCollection {
 
 /// Conformance for `${node.name}`` to the Sequence protocol.
 extension ${node.name}: Sequence {
+  fileprivate static func nextElement<Iter>(
+    _ iterator: inout Iter, parent: _SyntaxBase
+  ) -> ${node.collection_element_type}? where Iter: AbsoluteRawSyntaxIteratorProtocol {
+    guard let absoluteRaw = iterator.next() else { return nil }
+    let data = SyntaxData(absoluteRaw, parent: parent)
+%   is_constructable = node.collection_element_type != 'Syntax' and \
+%       not (element_node and element_node.is_base())
+%   if is_constructable:
+    return ${node.collection_element_type}(data)
+%   else:
+%     cast = '' if node.collection_element_type == 'Syntax' \
+%         else 'as! ' + node.collection_element_type
+    return (makeSyntax(data) ${cast})
+%   end
+  }
+
   public struct Iterator: IteratorProtocol {
     private let parent: _SyntaxBase
     private var iterator: PresentRawSyntaxChildren.Iterator
@@ -167,24 +183,45 @@ extension ${node.name}: Sequence {
     }
 
     public mutating func next() -> ${node.collection_element_type}? {
-      guard let absoluteRaw = iterator.next() else { return nil }
-      let data = SyntaxData(absoluteRaw, parent: self.parent)
-%   is_constructable = node.collection_element_type != 'Syntax' and \
-%       not (element_node and element_node.is_base())
-%   if is_constructable:
-      return ${node.collection_element_type}(data)
-%   else:
-%     cast = '' if node.collection_element_type == 'Syntax' \
-%         else 'as! ' + node.collection_element_type
-      return (makeSyntax(data) ${cast})
-%   end
+      return ${node.name}.nextElement(&iterator, parent: parent)
     }
   }
 
   /// Returns an iterator over the elements of this syntax collection.
   public func makeIterator() -> Iterator {
     return Iterator(collection: self)
   }
+
+  public func reversed() -> Reversed {
+    return Reversed(collection: self)
+  }
+
+  public struct Reversed: Sequence {
+    public struct Iterator: IteratorProtocol {
+      private let parent: _SyntaxBase
+      private var iterator: ReversedPresentRawSyntaxChildren.Iterator
+
+      public init(collection node: ${node.name}) {
+        self.iterator = .init(parent: node.data.absoluteRaw)
+        self.parent = node
+      }
+
+      public mutating func next() -> ${node.collection_element_type}? {
+        return ${node.name}.nextElement(&iterator, parent: parent)
+      }
+    }
+
+    let collection: ${node.name}
+
+    /// Returns an iterator over the elements of this syntax collection.
+    public func makeIterator() -> Iterator {
+      return Iterator(collection: collection)
+    }
+
+    public func reversed() -> ${node.name} {
+      return collection
+    }
+  }
 }
 
 %   end

Tests/SwiftSyntaxTest/SyntaxCollections.swift

@@ -18,6 +18,7 @@ public class SyntaxCollectionsAPITestCase: XCTestCase {
     ("testRemovingLastElement", testRemovingLastElement),
     ("testRemovingElement", testRemovingElement),
     ("testReplacingElement", testReplacingElement),
+    ("testIteration", testIteration),
   ]
 
   public func testAppendingElement() {
@@ -112,4 +113,30 @@ public class SyntaxCollectionsAPITestCase: XCTestCase {
       XCTAssertNotNil(newArrayElementList.child(at: 2))
       XCTAssertEqual("\(newArrayElementList.child(at: 2)!)", "3")
   }
+
+  public func testIteration() {
+    let arrayElementList = SyntaxFactory.makeArrayElementList([
+        integerLiteralElement(0),
+        integerLiteralElement(1),
+        integerLiteralElement(2)
+    ])
+
+    let elems = Array(arrayElementList)
+    XCTAssertEqual(elems.count, 3)
+    guard elems.count == 3 else {
+      return
+    }
+    XCTAssertEqual("\(elems[0])", "0")
+    XCTAssertEqual("\(elems[1])", "1")
+    XCTAssertEqual("\(elems[2])", "2")
+
+    let relems = Array(arrayElementList.reversed())
+    XCTAssertEqual(relems.count, 3)
+    guard relems.count == 3 else {
+      return
+    }
+    XCTAssertEqual("\(relems[2])", "0")
+    XCTAssertEqual("\(relems[1])", "1")
+    XCTAssertEqual("\(relems[0])", "2")
+  }
 }