Minor optimization for caching platform fonts

Sources/HTMLStreamer/AttributedStringConverter.swift

@@ -19,7 +19,8 @@ private typealias PlatformFont = NSFont
 
 public class AttributedStringConverter<Callbacks: HTMLConversionCallbacks> {
     private let configuration: AttributedStringConverterConfiguration
-    private var fontCache: [FontTrait: PlatformFont] = [:]
+    // There are only 8 combinations of FontTraits
+    private var fontCache: [PlatformFont?] = Array(repeating: nil, count: 8)
     
     private var tokenizer: Tokenizer<String.UnicodeScalarView.Iterator>!
     private var str: NSMutableAttributedString!
@@ -340,7 +341,7 @@ public class AttributedStringConverter<Callbacks: HTMLConversionCallbacks> {
     }
     
     private func getFont(traits: FontTrait) -> PlatformFont? {
-        if let cached = fontCache[traits] {
+        if let cached = fontCache[traits.rawValue] {
             return cached
         }
         
@@ -355,10 +356,20 @@ public class AttributedStringConverter<Callbacks: HTMLConversionCallbacks> {
         } else if traits.contains(.italic),
            let italic = descriptor.withSymbolicTraits(.traitItalic) {
             descriptor = italic
+        } else {
+            // N.B.: this does not go through the UIFontMetrics, the configuration fonts are expected to be setup for Dynamic Type already
+            fontCache[traits.rawValue] = baseFont
+            return baseFont
         }
         let font = PlatformFont(descriptor: descriptor, size: 0)
-        fontCache[traits] = font
+        #if os(iOS) || os(visionOS)
+        let scaled = configuration.fontMetrics.scaledFont(for: font)
+        fontCache[traits.rawValue] = scaled
+        return scaled
+        #else
+        fontCache[traits.rawValue] = font
         return font
+        #endif
     }
 }
 
@@ -366,6 +377,7 @@ public struct AttributedStringConverterConfiguration {
     #if os(iOS) || os(visionOS)
     public var font: UIFont
     public var monospaceFont: UIFont
+    public var fontMetrics: UIFontMetrics
     public var color: UIColor
     #elseif os(macOS)
     public var font: NSFont
@@ -375,9 +387,10 @@ public struct AttributedStringConverterConfiguration {
     public var paragraphStyle: NSParagraphStyle
     
     #if os(iOS) || os(visionOS)
-    public init(font: UIFont, monospaceFont: UIFont, color: UIColor, paragraphStyle: NSParagraphStyle) {
+    public init(font: UIFont, monospaceFont: UIFont, fontMetrics: UIFontMetrics, color: UIColor, paragraphStyle: NSParagraphStyle) {
         self.font = font
         self.monospaceFont = monospaceFont
+        self.fontMetrics = fontMetrics
         self.color = color
         self.paragraphStyle = paragraphStyle
     }

Tests/HTMLStreamerTests/AttributedStringConverterTests.swift

@@ -44,12 +44,22 @@ final class AttributedStringConverterTests: XCTestCase {
     }
     
     private func convert<Callbacks: HTMLConversionCallbacks>(_ html: String, callbacks _: Callbacks.Type = Callbacks.self) -> NSAttributedString {
+        #if os(iOS) || os(visionOS)
+        let config = AttributedStringConverterConfiguration(
+            font: font,
+            monospaceFont: monospaceFont,
+            fontMetrics: .default,
+            color: color,
+            paragraphStyle: .default
+        )
+        #else
         let config = AttributedStringConverterConfiguration(
             font: font,
             monospaceFont: monospaceFont,
             color: color,
             paragraphStyle: .default
         )
+        #endif
         let converter = AttributedStringConverter<Callbacks>(configuration: config)
         return converter.convert(html: html)
     }