Fix rendering thematic break with centered or right aligned text (#114)

Author: Guille Gonzalez

Sources/MarkdownUI/Rendering/AttributedStringRenderer.swift

@@ -353,7 +353,7 @@ extension AttributedStringRenderer {
 
     result.addAttribute(
       .paragraphStyle,
-      value: paragraphStyle(state: state),
+      value: paragraphStyle(state: state, alignment: .natural),
       range: NSRange(0..<result.length)
     )
 
@@ -492,12 +492,12 @@ extension AttributedStringRenderer {
       } ?? NSAttributedString()
   }
 
-  private func paragraphStyle(state: State) -> NSParagraphStyle {
+  private func paragraphStyle(state: State, alignment: NSTextAlignment? = nil) -> NSParagraphStyle {
     let pointSize = state.font.resolve(sizeCategory: environment.sizeCategory).pointSize
     let result = NSMutableParagraphStyle()
     result.setParagraphStyle(.default)
     result.baseWritingDirection = environment.baseWritingDirection
-    result.alignment = environment.alignment
+    result.alignment = alignment ?? environment.alignment
     result.lineSpacing = environment.lineSpacing
     result.paragraphSpacing = round(pointSize * state.paragraphSpacing)
     result.headIndent = round(pointSize * state.headIndent)

Tests/MarkdownUITests/MarkdownTests.swift

@@ -397,6 +397,33 @@
       assertSnapshot(matching: view, as: .image(layout: layout), named: platformName)
     }
 
+    func testThematicBreakAndCenterAlignment() {
+      let view = Markdown(
+        #"""
+        # SwiftUI
+
+        Declare the user interface and behavior for your app
+        on every platform.
+
+        ---
+
+        ## Overview
+
+        SwiftUI provides views, controls, and layout structures
+        for declaring your app’s user interface.
+
+        ---
+
+        ― From Apple Developer Documentation
+        """#
+      )
+      .multilineTextAlignment(.center)
+      .background(Color.orange)
+      .padding()
+
+      assertSnapshot(matching: view, as: .image(layout: layout), named: platformName)
+    }
+
     func testInlines() {
       let view = Markdown(
         #"""