[SyntaxRewriter] Iterate RawSyntaxChildren using pattern matching

Simpify the iteration code.
Also, stop counting 'childIndex' as it can be retrieved from the
absolute info.

Author: rintaro

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/SyntaxRewriterFile.swift

@@ -318,15 +318,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         // with 'Syntax'
         var rewrittens: ContiguousArray<RetainedSyntaxArena> = []
 
-        // Incrementing i manually is faster than using .enumerated()
-        var childIndex = 0
-        for (raw, info) in RawSyntaxChildren(node) {
-          defer { childIndex += 1 }
-
-          guard let child = raw, viewMode.shouldTraverse(node: child) else {
-            // Node does not exist or should not be visited.
-            continue
-          }
+        for case let (child?, info) in RawSyntaxChildren(node) where viewMode.shouldTraverse(node: child) {
 
           // Build the Syntax node to rewrite
           var childNode = nodeFactory.create(parent: node, raw: child, absoluteInfo: info)
@@ -343,7 +335,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
             }
 
             // Update the rewritten child.
-            newLayout[childIndex] = childNode.raw
+            newLayout[Int(info.indexInParent)] = childNode.raw
             // Retain the syntax arena of the new node until it's wrapped with Syntax node.
             rewrittens.append(childNode.raw.arenaReference.retained)
           }

Sources/SwiftSyntax/generated/SyntaxRewriter.swift

@@ -3915,17 +3915,7 @@ open class SyntaxRewriter {
     // with 'Syntax'
     var rewrittens: ContiguousArray<RetainedSyntaxArena> = []
 
-    // Incrementing i manually is faster than using .enumerated()
-    var childIndex = 0
-    for (raw, info) in RawSyntaxChildren(node) {
-      defer {
-        childIndex += 1
-      }
-
-      guard let child = raw, viewMode.shouldTraverse(node: child) else {
-        // Node does not exist or should not be visited.
-        continue
-      }
+    for case let (child?, info) in RawSyntaxChildren(node) where viewMode.shouldTraverse(node: child) {
 
       // Build the Syntax node to rewrite
       var childNode = nodeFactory.create(parent: node, raw: child, absoluteInfo: info)
@@ -3942,7 +3932,7 @@ open class SyntaxRewriter {
         }
 
         // Update the rewritten child.
-        newLayout[childIndex] = childNode.raw
+        newLayout[Int(info.indexInParent)] = childNode.raw
         // Retain the syntax arena of the new node until it's wrapped with Syntax node.
         rewrittens.append(childNode.raw.arenaReference.retained)
       }