Make change backwards-compatible

Author: Samasaur1

Sources/Markdown/Walker/Walkers/MarkupFormatter.swift

@@ -279,7 +279,7 @@ public struct MarkupFormatter: MarkupWalker {
                     thematicBreakCharacter: ThematicBreakCharacter = .dash,
                     thematicBreakLength: UInt = 5,
                     emphasisMarker: EmphasisMarker = .star,
-                    strongEmphasisMarker: EmphasisMarker = .star,
+                    strongEmphasisMarker: EmphasisMarker? = nil,
                     condenseAutolinks: Bool = true,
                     preferredHeadingStyle: PreferredHeadingStyle = .atx,
                     preferredLineLimit: PreferredLineLimit? = nil,
@@ -291,7 +291,7 @@ public struct MarkupFormatter: MarkupWalker {
             self.defaultCodeBlockLanguage = defaultCodeBlockLanguage
             self.thematicBreakCharacter = thematicBreakCharacter
             self.emphasisMarker = emphasisMarker
-            self.strongEmphasisMarker = strongEmphasisMarker
+            self.strongEmphasisMarker = strongEmphasisMarker ?? emphasisMarker
             self.condenseAutolinks = condenseAutolinks
             self.preferredHeadingStyle = preferredHeadingStyle
             self.preferredLineLimit = preferredLineLimit

Tests/MarkdownTests/Visitors/MarkupFormatterTests.swift

@@ -531,6 +531,23 @@ class MarkupFormatterOptionsTests: XCTestCase {
             let underline = "__strong__"
             let star = "**strong**"
 
+            do {
+                let document = Document(parsing: underline)
+                let printed = document.format(options: .init(emphasisMarker: .star))
+                XCTAssertEqual(star, printed)
+            }
+
+            do {
+                let document = Document(parsing: star)
+                let printed = document.format(options: .init(emphasisMarker: .underline))
+                XCTAssertEqual(underline, printed)
+            }
+        }
+
+        do {
+            let underline = "__strong__"
+            let star = "**strong**"
+
             do {
                 let document = Document(parsing: underline)
                 let printed = document.format(options: .init(strongEmphasisMarker: .star))
@@ -542,7 +559,23 @@ class MarkupFormatterOptionsTests: XCTestCase {
                 let printed = document.format(options: .init(strongEmphasisMarker: .underline))
                 XCTAssertEqual(underline, printed)
             }
+        }
+
+        do {
+            let underline = "__strong__"
+            let star = "**strong**"
 
+            do {
+                let document = Document(parsing: underline)
+                let printed = document.format(options: .init(emphasisMarker: .underline, strongEmphasisMarker: .star))
+                XCTAssertEqual(star, printed)
+            }
+
+            do {
+                let document = Document(parsing: star)
+                let printed = document.format(options: .init(emphasisMarker: .star, strongEmphasisMarker: .underline))
+                XCTAssertEqual(underline, printed)
+            }
         }
     }