Preserve the blank lines typed after a list

The newline to break replacement only matched paragraph to paragraph, so a blank
line after a list was dropped and the text following it glued to the last item.
Only a following paragraph is matched, because without a blank line its text
would have continued the last item instead of starting a paragraph of its own.

ElementX/Sources/Other/Extensions/String.swift

@@ -52,9 +52,10 @@ nonisolated extension String {
 }
 
 nonisolated extension String {
+    /// Drops stray new lines everywhere but paragraphs and lists when other paragraphs follow them
     func replacingHtmlBreaksOccurrences() -> String {
         var result = self
-        let pattern = #"</p>(\n+)<p>"#
+        let pattern = #"</(p|ul|ol)>(\n+)(?=<p[ >])"#
         
         guard let regex = try? NSRegularExpression(pattern: pattern, options: []) else {
             return result
@@ -63,11 +64,12 @@ nonisolated extension String {
         
         for match in matches.reversed() {
             guard let range = Range(match.range, in: self),
-                  let innerMatchRange = Range(match.range(at: 1), in: self) else {
+                  let tagRange = Range(match.range(at: 1), in: self),
+                  let innerMatchRange = Range(match.range(at: 2), in: self) else {
                 continue
             }
             let numberOfBreaks = (self[innerMatchRange].components(separatedBy: "\n").count - 1)
-            let replacement = "<br>" + String(repeating: "<br>", count: numberOfBreaks)
+            let replacement = "</\(self[tagRange])>" + String(repeating: "<br>", count: numberOfBreaks)
             result.replaceSubrange(range, with: replacement)
         }
         

UnitTests/Sources/AttributedStringBuilderTests.swift

@@ -684,6 +684,41 @@ struct AttributedStringBuilderTests {
         }
     }
     
+    /// A blank line the user typed after a list must survive, just like one between two paragraphs.
+    @Test
+    func newLineAfterList() throws {
+        let htmlString = "<p>Line 1</p>\n<ul>\n<li>Line 2</li>\n</ul>\n<p>Line 4</p>\n"
+        
+        let attributedString = try #require(attributedStringBuilder.fromHTML(htmlString), "Could not build the attributed string")
+        
+        #expect(String(attributedString.characters) == "Line 1\n  • Line 2\n\nLine 4")
+    }
+    
+    /// Without a blank line the trailing text is a lazy continuation of the item, so it stays on its line.
+    @Test
+    func noNewLineAfterList() throws {
+        let htmlString = "<ul><li>Line 1</li></ul><p>Line 2</p>"
+        
+        let attributedString = try #require(attributedStringBuilder.fromHTML(htmlString), "Could not build the attributed string")
+        
+        #expect(String(attributedString.characters) == "  • Line 1\nLine 2")
+    }
+    
+    /// A blank line is preserved wherever it can be told apart from mere block separation.
+    @Test
+    func newLinesBetweenBlocks() throws {
+        let expectations = ["<p>a</p>\n<p>b</p>": "a\n\nb",
+                            "<p>a</p>\n\n<p>b</p>": "a\n\n\nb",
+                            "<ol start=\"2\"><li>a</li></ol>\n<p>b</p>": "  2. a\n\nb",
+                            // A list can interrupt a paragraph, so this newline is block separation.
+                            "<p>a</p>\n<ul><li>b</li></ul>": "a\n  • b"]
+        
+        for (htmlString, expectation) in expectations {
+            let attributedString = try #require(attributedStringBuilder.fromHTML(htmlString), "Could not build the attributed string")
+            #expect(String(attributedString.characters) == expectation, "Wrong rendering for \(htmlString)")
+        }
+    }
+    
     @Test
     func unorderedList() throws {
         let htmlString = "<ul><li>1</li><li>2</li><li>3</li></ul>"

UnitTests/Sources/StringTests.swift

@@ -73,13 +73,18 @@ struct StringTests {
         let input3 = "</p>\n\n\n\n<p>"
         let input4 = "<p>a</p>\n<p>b</p>"
         let input5 = "empty"
+        let input6 = "<ul><li>a</li></ul>\n<p>b</p>"
+        let input7 = "</p>\n<ul>"
         
         let expectedOutput0 = input0
-        let expectedOutput1 = "<br><br>"
-        let expectedOutput2 = "<br><br><br>"
-        let expectedOutput3 = "<br><br><br><br><br>"
-        let expectedOutput4 = "<p>a<br><br>b</p>"
+        let expectedOutput1 = "</p><br><p>"
+        let expectedOutput2 = "</p><br><br><p>"
+        let expectedOutput3 = "</p><br><br><br><br><p>"
+        let expectedOutput4 = "<p>a</p><br><p>b</p>"
         let expectedOutput5 = input5
+        let expectedOutput6 = "<ul><li>a</li></ul><br><p>b</p>"
+        // A list can interrupt a paragraph, so this newline isn't a blank line the user typed.
+        let expectedOutput7 = input7
         
         #expect(input0.replacingHtmlBreaksOccurrences() == expectedOutput0)
         #expect(input1.replacingHtmlBreaksOccurrences() == expectedOutput1)
@@ -87,5 +92,7 @@ struct StringTests {
         #expect(input3.replacingHtmlBreaksOccurrences() == expectedOutput3)
         #expect(input4.replacingHtmlBreaksOccurrences() == expectedOutput4)
         #expect(input5.replacingHtmlBreaksOccurrences() == expectedOutput5)
+        #expect(input6.replacingHtmlBreaksOccurrences() == expectedOutput6)
+        #expect(input7.replacingHtmlBreaksOccurrences() == expectedOutput7)
     }
 }