Add delete highlights

Sources/SwiftDocC/Model/Rendering/References/FileReference.swift

@@ -39,6 +39,9 @@ public struct FileReference: RenderReference, Equatable {
     /// The line highlights for this file.
     public var highlights: [LineHighlighter.Highlight] = []
 
+    /// The delete line highlights for this file.
+    public var deleteHighlights: [LineHighlighter.Highlight] = []
+
     /// Creates a new file reference.
     ///
     /// - Parameters:
@@ -54,14 +57,16 @@ public struct FileReference: RenderReference, Equatable {
         fileType: String,
         syntax: String,
         content: [String],
-        highlights: [LineHighlighter.Highlight] = []
+        highlights: [LineHighlighter.Highlight] = [],
+        deleteHighlights: [LineHighlighter.Highlight] = []
     ) {
         self.identifier = identifier
         self.fileName = fileName
         self.fileType = fileType
         self.syntax = syntax
         self.content = content
         self.highlights = highlights
+        self.deleteHighlights = deleteHighlights
     }
 
     public init(from decoder: Decoder) throws {
@@ -73,6 +78,7 @@ public struct FileReference: RenderReference, Equatable {
         syntax = try values.decode(String.self, forKey: .syntax)
         content = try values.decode([String].self, forKey: .content)
         highlights = try values.decodeIfPresent([LineHighlighter.Highlight].self, forKey: .highlights) ?? []
+        deleteHighlights = (try? values.decodeIfPresent([LineHighlighter.Highlight].self, forKey: .deleteHighlights)) ?? []
     }
 }
 

Sources/SwiftDocC/Model/Rendering/RenderNodeTranslator.swift

@@ -129,6 +129,7 @@ public struct RenderNodeTranslator: SemanticVisitor {
         // Add the highlights to the file references.
         for result in highlightsPerFile {
             fileReferences[result.file.path]?.highlights = result.highlights
+            fileReferences[result.file.path]?.deleteHighlights = result.deleteHighlights
         }
 
         return TutorialSectionsRenderSection.Section(title: tutorialSection.title, contentSection: introduction, stepsSection: stepsContent, anchor: urlReadableFragment(tutorialSection.title))

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

@@ -56,6 +56,9 @@ public struct LineHighlighter {
 
         /// The highlights to apply when displaying this file.
         let highlights: [Highlight]
+
+        /// The delete highlights to apply when displaying this file.
+        let deleteHighlights: [Highlight]
     }
 
     /**
@@ -121,7 +124,7 @@ public struct LineHighlighter {
     private func lineHighlights(old: 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: [])
+            return Result(file: new, highlights: [], deleteHighlights: [])
         }
 
         let diff = newLines.difference(from: oldLines)
@@ -134,22 +137,29 @@ public struct LineHighlighter {
             return Highlight(line: offset + 1)
         }
 
-        return Result(file: new, highlights: highlights)
+        let deleteHighlights = diff.removals.compactMap { removal -> Highlight? in
+            guard case .remove(let offset, _, _) = removal else { return nil }
+            // Use 1-based indexing for line numbers.
+            // TODO: Collect intra-line diffs.
+            return Highlight(line: offset + 1)
+        }
+
+        return Result(file: new, highlights: highlights, deleteHighlights: deleteHighlights)
     }
 
     /// Returns the line highlights between two ``Code`` elements.
     private func lineHighlights(old: Code?, new: Code) -> Result {
         if let previousFileOverride = new.previousFileReference {
             guard !new.shouldResetDiff else {
-                return Result(file: new.fileReference, highlights: [])
+                return Result(file: new.fileReference, highlights: [], deleteHighlights: [])
             }
             return lineHighlights(old: previousFileOverride, new: new.fileReference)
         }
 
         guard let old = old,
             old.fileName == new.fileName,
             !new.shouldResetDiff else {
-                return Result(file: new.fileReference, highlights: [])
+                return Result(file: new.fileReference, highlights: [], deleteHighlights: [])
         }
 
         return lineHighlights(old: old.fileReference, new: new.fileReference)