Resolve fonts considering the environment's size category (#94)

* Resolve fonts considering the environment's size category

* Fix generation of README images

Sources/MarkdownUI/Markdown.swift

@@ -253,6 +253,7 @@ public struct Markdown: View {
         layoutDirection: self.layoutDirection,
         textAlignment: self.textAlignment
       ),
+      sizeCategory: self.sizeCategory,
       style: self.style,
       imageHandlers: self.imageHandlers
     )

Sources/MarkdownUI/Rendering/AttributedStringRenderer.swift

@@ -39,6 +39,7 @@ struct AttributedStringRenderer {
   let baseURL: URL?
   let baseWritingDirection: NSWritingDirection
   let alignment: NSTextAlignment
+  let sizeCategory: ContentSizeCategory
   let style: MarkdownStyle
 
   func renderDocument(_ document: Document) -> NSAttributedString {
@@ -174,7 +175,7 @@ extension AttributedStringRenderer {
       style.measurements.headIndentStep,
       NSAttributedString(
         string: "\(highestNumber).",
-        attributes: [.font: state.font.monospacedDigit().resolve()]
+        attributes: [.font: state.font.monospacedDigit().resolve(sizeCategory: sizeCategory)]
       ).em() + style.measurements.listMarkerSpacing
     )
 
@@ -341,7 +342,7 @@ extension AttributedStringRenderer {
       .init(
         string: .nbsp,
         attributes: [
-          .font: state.font.resolve(),
+          .font: state.font.resolve(sizeCategory: sizeCategory),
           .strikethroughStyle: NSUnderlineStyle.single.rawValue,
           .strikethroughColor: PlatformColor.separator,
         ]
@@ -424,7 +425,7 @@ extension AttributedStringRenderer {
     NSAttributedString(
       string: text,
       attributes: [
-        .font: state.font.resolve(),
+        .font: state.font.resolve(sizeCategory: sizeCategory),
         .foregroundColor: PlatformColor(state.foregroundColor),
       ]
     )
@@ -490,7 +491,7 @@ extension AttributedStringRenderer {
   }
 
   private func paragraphStyle(state: State) -> NSParagraphStyle {
-    let pointSize = state.font.resolve().pointSize
+    let pointSize = state.font.resolve(sizeCategory: sizeCategory).pointSize
     let result = NSMutableParagraphStyle()
     result.setParagraphStyle(.default)
     result.baseWritingDirection = baseWritingDirection

Sources/MarkdownUI/Rendering/Document+NSAttributedString.swift

@@ -7,12 +7,14 @@ extension Document {
     baseURL: URL?,
     baseWritingDirection: NSWritingDirection,
     alignment: NSTextAlignment,
+    sizeCategory: ContentSizeCategory,
     style: MarkdownStyle
   ) -> NSAttributedString {
     AttributedStringRenderer(
       baseURL: baseURL,
       baseWritingDirection: baseWritingDirection,
       alignment: alignment,
+      sizeCategory: sizeCategory,
       style: style
     ).renderDocument(self)
   }
@@ -21,6 +23,7 @@ extension Document {
     baseURL: URL?,
     baseWritingDirection: NSWritingDirection,
     alignment: NSTextAlignment,
+    sizeCategory: ContentSizeCategory,
     style: MarkdownStyle,
     imageHandlers: [String: MarkdownImageHandler]
   ) -> AnyPublisher<NSAttributedString, Never> {
@@ -30,6 +33,7 @@ extension Document {
           baseURL: baseURL,
           baseWritingDirection: baseWritingDirection,
           alignment: alignment,
+          sizeCategory: sizeCategory,
           style: style
         )
       )

Sources/MarkdownUI/Style/Font.swift

@@ -8,15 +8,15 @@ extension MarkdownStyle {
   public struct Font: Hashable {
     private var provider: AnyHashable
 
-    func resolve() -> PlatformFont {
+    func resolve(sizeCategory: ContentSizeCategory = .large) -> PlatformFont {
       guard let fontProvider = self.provider.base as? FontProvider else {
         fatalError("provider should conform to FontProvider")
       }
       #if os(macOS)
-        return .init(descriptor: fontProvider.fontDescriptor(), size: 0)
+        return .init(descriptor: fontProvider.fontDescriptor(compatibleWith: sizeCategory), size: 0)
           ?? .preferredFont(forTextStyle: .body)
       #elseif os(iOS) || os(tvOS)
-        return .init(descriptor: fontProvider.fontDescriptor(), size: 0)
+        return .init(descriptor: fontProvider.fontDescriptor(compatibleWith: sizeCategory), size: 0)
       #endif
     }
   }
@@ -150,21 +150,22 @@ extension MarkdownStyle.Font {
 // MARK: - FontProvider
 
 private protocol FontProvider {
-  func fontDescriptor() -> PlatformFontDescriptor
+  func fontDescriptor(compatibleWith sizeCategory: ContentSizeCategory) -> PlatformFontDescriptor
 }
 
 private struct TextStyleFontProvider: Hashable, FontProvider {
   var style: SwiftUI.Font.TextStyle
   var design: SwiftUI.Font.Design
 
-  func fontDescriptor() -> PlatformFontDescriptor {
+  func fontDescriptor(compatibleWith sizeCategory: ContentSizeCategory) -> PlatformFontDescriptor {
     #if os(macOS)
       let fontDescriptor = PlatformFontDescriptor.preferredFontDescriptor(
         forTextStyle: .init(style)
       )
     #elseif os(iOS) || os(tvOS)
       let fontDescriptor = PlatformFontDescriptor.preferredFontDescriptor(
-        withTextStyle: .init(style)
+        withTextStyle: .init(style),
+        compatibleWith: .init(preferredContentSizeCategory: .init(sizeCategory))
       )
     #endif
 
@@ -177,7 +178,7 @@ private struct SystemFontProvider: Hashable, FontProvider {
   var weight: SwiftUI.Font.Weight
   var design: SwiftUI.Font.Design
 
-  func fontDescriptor() -> PlatformFontDescriptor {
+  func fontDescriptor(compatibleWith _: ContentSizeCategory) -> PlatformFontDescriptor {
     let fontDescriptor = PlatformFont.systemFont(ofSize: size, weight: .init(weight))
       .fontDescriptor
     return fontDescriptor.withDesign(.init(design)) ?? fontDescriptor
@@ -189,12 +190,16 @@ private struct CustomFontProvider: Hashable, FontProvider {
   var size: CGFloat
   var textStyle: SwiftUI.Font.TextStyle?
 
-  func fontDescriptor() -> PlatformFontDescriptor {
+  func fontDescriptor(compatibleWith sizeCategory: ContentSizeCategory) -> PlatformFontDescriptor {
     var size = self.size
 
     #if os(iOS) || os(tvOS)
       if let textStyle = self.textStyle {
-        size = UIFontMetrics(forTextStyle: .init(textStyle)).scaledValue(for: size)
+        size = UIFontMetrics(forTextStyle: .init(textStyle))
+          .scaledValue(
+            for: size,
+            compatibleWith: .init(preferredContentSizeCategory: .init(sizeCategory))
+          )
       }
     #endif
 
@@ -211,11 +216,11 @@ private struct FontModifierProvider<M>: Hashable, FontProvider where M: Hashable
   var base: AnyHashable
   var modifier: M
 
-  func fontDescriptor() -> PlatformFontDescriptor {
+  func fontDescriptor(compatibleWith sizeCategory: ContentSizeCategory) -> PlatformFontDescriptor {
     guard let fontProvider = self.base.base as? FontProvider else {
       fatalError("base should conform to FontProvider")
     }
-    var fontDescriptor = fontProvider.fontDescriptor()
+    var fontDescriptor = fontProvider.fontDescriptor(compatibleWith: sizeCategory)
     modifier.modify(&fontDescriptor)
     return fontDescriptor
   }
@@ -399,3 +404,38 @@ extension PlatformFontDescriptor.SystemDesign {
     }
   }
 }
+
+#if os(iOS) || os(tvOS)
+  extension UIContentSizeCategory {
+    fileprivate init(_ contentSizeCategory: ContentSizeCategory) {
+      switch contentSizeCategory {
+      case .extraSmall:
+        self = .extraSmall
+      case .small:
+        self = .small
+      case .medium:
+        self = .medium
+      case .large:
+        self = .large
+      case .extraLarge:
+        self = .extraLarge
+      case .extraExtraLarge:
+        self = .extraExtraLarge
+      case .extraExtraExtraLarge:
+        self = .extraExtraExtraLarge
+      case .accessibilityMedium:
+        self = .accessibilityMedium
+      case .accessibilityLarge:
+        self = .accessibilityLarge
+      case .accessibilityExtraLarge:
+        self = .accessibilityExtraLarge
+      case .accessibilityExtraExtraLarge:
+        self = .accessibilityExtraExtraLarge
+      case .accessibilityExtraExtraExtraLarge:
+        self = .accessibilityExtraExtraExtraLarge
+      @unknown default:
+        self = .large
+      }
+    }
+  }
+#endif

Tests/MarkdownUITests/MarkdownTests.swift

@@ -449,5 +449,20 @@
 
       assertSnapshot(matching: view, as: .image(layout: layout), named: platformName)
     }
+
+    #if os(iOS)
+      func testSizeCategory() {
+        let view = VStack {
+          ForEach(ContentSizeCategory.allCases, id: \.self) { sizeCategory in
+            Markdown("Markdown**UI**")
+              .environment(\.sizeCategory, sizeCategory)
+          }
+        }
+        .background(Color.orange)
+        .padding()
+
+        assertSnapshot(matching: view, as: .image(layout: layout), named: platformName)
+      }
+    #endif
   }
 #endif

Tests/MarkdownUITests/ReadMeImagesTests.swift

@@ -48,6 +48,7 @@
       )
     }
 
+    @available(iOS 15.0, *)
     func testMarkdownStyle() {
       let view = Markdown(
         #"""