Avoid a few possible unnecessary copies in low level implementation details (#1296)

* Declare a few private types as non-copyable to avoid unintentional copies of data in low level implementation details

* Avoid potential unnecessary copies when highlighting tutorial code steps

Author: d-ronnqvist

Sources/SwiftDocC/Infrastructure/Link Resolution/PathHierarchy+PathComponent.swift

@@ -210,7 +210,7 @@ extension PathHierarchy.PathParser {
     }
 }
 
-private struct PathComponentScanner {
+private struct PathComponentScanner: ~Copyable {
     private var remaining: Substring
 
     static let separator: Character = "/"

Sources/SwiftDocC/Infrastructure/Link Resolution/PathHierarchy+TypeSignature.swift

@@ -230,7 +230,7 @@ extension PathHierarchy {
     }
 
     /// A small helper type that tracks the scope of nested brackets; `()`, `[]`, or `<>`.
-    private struct SwiftBracketsStack {
+    private struct SwiftBracketsStack: ~Copyable {
         enum Bracket {
             case angle  // <>
             case square // []
@@ -522,7 +522,7 @@ extension PathHierarchy.PathParser {
 
 // MARK: Scanning a substring
 
-private struct StringScanner {
+private struct StringScanner: ~Copyable {
     private var remaining: Substring
 
     init(_ original: Substring) {

Sources/SwiftDocC/Infrastructure/Link Resolution/PathHierarchy+TypeSignatureDisambiguation.swift

@@ -63,7 +63,7 @@ extension PathHierarchy.DisambiguationContainer {
         }
     }
 
-    private static func _minimalSuggestedDisambiguationForFewParameters(typeNames: Table<String>) -> [[String]?] {
+    private static func _minimalSuggestedDisambiguationForFewParameters(typeNames: consuming Table<String>) -> [[String]?] {
         typealias IntSet = _TinySmallValueIntSet
         // We find the minimal suggested type-signature disambiguation in two steps.
         //
@@ -216,7 +216,7 @@ extension PathHierarchy.DisambiguationContainer {
         }
     }
 
-    private static func _minimalSuggestedDisambiguationForManyParameters(typeNames: Table<String>) -> [[String]?] {
+    private static func _minimalSuggestedDisambiguationForManyParameters(typeNames: consuming Table<String>) -> [[String]?] {
         // If there are more than 64 parameters or more than 64 overloads we only try to disambiguate by a single type name.
         //
         // In practice, the number of parameters goes down rather quickly.
@@ -418,7 +418,7 @@ extension _TinySmallValueIntSet {
 // MARK: Table
 
 /// A fixed-size grid of elements.
-private struct Table<Element> {
+private struct Table<Element>: ~Copyable {
     typealias Size = (width: Int, height: Int)
     @usableFromInline
     let size: Size

Sources/SwiftDocC/Model/Rendering/Tutorial/LineHighlighter.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
+ Copyright (c) 2021-2025 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
@@ -30,23 +30,6 @@ import Foundation
  ```
  */
 public struct LineHighlighter {
-    /**
-     A local utility type to hold incremental results.
-    */
-    private struct IncrementalResult {
-        /// The previous ``Code`` element to compare.
-        /// If this is the first ``Step``'s ``Code``, this will be `nil`.
-        let previousCode: Code?
-        
-        /// The highlight results accumulated so far.
-        let results: [Result]
-        
-        init(previousCode: Code? = nil, results: [Result] = []) {
-            self.previousCode = previousCode
-            self.results = results
-        }
-    }
-    
     /**
      The final resulting highlights for a given file.
      */
@@ -100,7 +83,7 @@ public struct LineHighlighter {
     }
 
     /// The lines in the `resource` file.
-    private func lines(of resource: ResourceReference) -> [String]? {
+    private func lines(of resource: borrowing ResourceReference) -> [String]? {
         let fileContent: String?
         // Check if the file is a local asset that can be read directly from the context
         if let fileData = try? context.resource(with: resource) {
@@ -118,7 +101,7 @@ public struct LineHighlighter {
     }
 
     /// Returns the line highlights between two files.
-    private func lineHighlights(old: ResourceReference, new: ResourceReference) -> Result {
+    private func lineHighlights(old: borrowing ResourceReference, new: ResourceReference) -> Result {
         // Retrieve the contents of the current file and the file we're comparing against.
         guard let oldLines = lines(of: old), let newLines = lines(of: new) else {
             return Result(file: new, highlights: [])
@@ -138,7 +121,7 @@ public struct LineHighlighter {
     }
 
     /// Returns the line highlights between two ``Code`` elements.
-    private func lineHighlights(old: Code?, new: Code) -> Result {
+    private func lineHighlights(old: consuming Code?, new: borrowing Code) -> Result {
         if let previousFileOverride = new.previousFileReference {
             guard !new.shouldResetDiff else {
                 return Result(file: new.fileReference, highlights: [])
@@ -157,11 +140,17 @@ public struct LineHighlighter {
 
     /// The highlights to apply for the given ``TutorialSection``.
     var highlights: [Result] {
-        return tutorialSection.stepsContent?.steps
-            .compactMap { $0.code }
-            .reduce(IncrementalResult(), { (incrementalResult, newCode) -> IncrementalResult in
-                let result = lineHighlights(old: incrementalResult.previousCode, new: newCode)
-                return IncrementalResult(previousCode: newCode, results: incrementalResult.results + [result])
-            }).results ?? []
+        guard let steps = tutorialSection.stepsContent?.steps else { return [] }
+        
+        var previousCode: Code? = nil
+        var results: [Result] = []
+        
+        for step in steps {
+            guard let newCode = step.code else { continue }
+            results.append(lineHighlights(old: previousCode, new: newCode))
+            previousCode = newCode
+        }
+        
+        return results
     }
 }

Sources/SwiftDocC/Utility/CollectionChanges.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2022 Apple Inc. and the Swift project authors
+ Copyright (c) 2022-2025 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
@@ -65,7 +65,7 @@ struct CollectionChanges {
 ///
 /// - Important:
 /// Removals need to be applied in reverse order. All removals need to be applied before applying any insertions. Insertions need to be applied in order.
-private struct ChangeSegmentBuilder {
+private struct ChangeSegmentBuilder: ~Copyable {
     typealias Segment = CollectionChanges.Segment
 
     private(set) var segments: [Segment]