FixContinuationStyle: sanitize each paragraph once instead of twice

src/libse/Forms/FixCommonErrors/FixContinuationStyle.cs

@@ -40,14 +40,22 @@ public void Fix(Subtitle subtitle, IFixCallbacks callbacks)
             var inSentence = false;
             bool? inItalicSentence = null;
 
+            // SanitizeString runs four regex replaces per call, and the loop sanitized every
+            // paragraph twice: once as pNext's text, then again as p's text one iteration later.
+            // Carry the sanitized "next" value forward instead. The carry is dropped whenever the
+            // loop writes pNext.Text below, so the following iteration re-sanitizes what the
+            // paragraph actually holds.
+            string carriedText = null;
+
             for (var i = 0; i < subtitle.Paragraphs.Count - 1; i++)
             {
                 var p = subtitle.Paragraphs[i];
                 var pNext = subtitle.Paragraphs[i + 1];
                 var oldText = p.Text;
                 var oldTextNext = pNext.Text;
-                var text = ContinuationUtilities.SanitizeString(p.Text);
+                var text = carriedText ?? ContinuationUtilities.SanitizeString(p.Text);
                 var textNext = ContinuationUtilities.SanitizeString(pNext.Text);
+                carriedText = textNext; // captured before the Arabic conversion below, which the next iteration reapplies
                 var isChecked = true;
                 var shouldProcess = true;
 
@@ -207,6 +215,7 @@ public void Fix(Subtitle subtitle, IFixCallbacks callbacks)
                             if (IsPreviewStep(callbacks) && isChecked || !IsPreviewStep(callbacks))
                             {
                                 pNext.Text = newTextNext;
+                                carriedText = null; // pNext.Text changed - the next iteration must re-sanitize
                             }
 
                             fixCount++;

tests/libse/Common/UtilitiesCountTagInTextTest.cs

@@ -0,0 +1,35 @@
+using Nikse.SubtitleEdit.Core.Common;
+
+namespace LibSETests.Common;
+
+public class UtilitiesCountTagInTextTest
+{
+    // The char overload has two implementations: MemoryExtensions.Count on net8+ and an
+    // IndexOf loop on netstandard2.1. Both must agree on these, in particular on a hit that
+    // lands on the very last index - the loop returns early from inside its body there.
+    [Theory]
+    [InlineData("", '"', 0)]
+    [InlineData("no quotes here", '"', 0)]
+    [InlineData("\"", '"', 1)]
+    [InlineData("say \"this\"", '"', 2)]
+    [InlineData("\"\"\"", '"', 3)]
+    [InlineData("- No.\r\n- Then stay.", '-', 2)]
+    [InlineData("{\\an8}{\\pos(10,20)}Hi", '{', 2)]
+    [InlineData("aaa", 'a', 3)]
+    public void CountsEveryOccurrenceOfChar(string text, char tag, int expected)
+    {
+        Assert.Equal(expected, Utilities.CountTagInText(text, tag));
+    }
+
+    // The char and string overloads are separate implementations; for a single-character tag
+    // they must not drift apart.
+    [Theory]
+    [InlineData("\"Are you coming?\" she asked.", '"')]
+    [InlineData("- Yes.\r\n- No.", '-')]
+    [InlineData("nothing to find", 'z')]
+    [InlineData("trailing hit-", '-')]
+    public void CharOverloadAgreesWithStringOverload(string text, char tag)
+    {
+        Assert.Equal(Utilities.CountTagInText(text, tag.ToString()), Utilities.CountTagInText(text, tag));
+    }
+}

tests/libse/Forms/FixCommonErrors/FixContinuationStyleTest.cs

@@ -0,0 +1,42 @@
+using Nikse.SubtitleEdit.Core.Common;
+using Nikse.SubtitleEdit.Core.Enums;
+using Nikse.SubtitleEdit.Core.Forms.FixCommonErrors;
+
+namespace LibSETests.Forms.FixCommonErrors;
+
+public class FixContinuationStyleTest
+{
+    // The rule walks paragraph pairs and carries paragraph i+1's sanitized text forward to use
+    // as paragraph i's on the next iteration, rather than sanitizing every paragraph twice.
+    // Carrying the wrong side of the pair still produces the right answer on a plain
+    // continuation chain, so this pins a case that actually discriminates: only paragraph 2
+    // continues into paragraph 3 (40 ms gap), while paragraph 1 ends a sentence and paragraph 4
+    // is too far away (1600 ms). Get the carry wrong and paragraph 2 keeps its dots-less text.
+    [Fact]
+    public void OnlyTheContinuingParagraphGetsTrailingDots()
+    {
+        var previousStyle = Configuration.Settings.General.ContinuationStyle;
+        try
+        {
+            Configuration.Settings.General.ContinuationStyle = ContinuationStyle.OnlyTrailingDots;
+
+            var subtitle = new Subtitle();
+            subtitle.Paragraphs.Add(new Paragraph("Wait!", 0, 1122));
+            subtitle.Paragraphs.Add(new Paragraph("I was going to tell you", 1162, 3083));
+            subtitle.Paragraphs.Add(new Paragraph("and now it is too late", 3123, 4220));
+            subtitle.Paragraphs.Add(new Paragraph("[door slams]", 5820, 7720));
+            subtitle.Renumber();
+
+            new FixContinuationStyle { FixAction = "act" }.Fix(subtitle, new EmptyFixCallback());
+
+            Assert.Equal("Wait!", subtitle.Paragraphs[0].Text);
+            Assert.Equal("I was going to tell you...", subtitle.Paragraphs[1].Text);
+            Assert.Equal("and now it is too late", subtitle.Paragraphs[2].Text);
+            Assert.Equal("[door slams]", subtitle.Paragraphs[3].Text);
+        }
+        finally
+        {
+            Configuration.Settings.General.ContinuationStyle = previousStyle;
+        }
+    }
+}