fix: 다른 앱에서 보이는 HTML — 빈 줄 <br>, 셀 속 그림 (상류 라운드 9 백포트)

CHANGELOG.md

@@ -6,6 +6,17 @@ and follows [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
+### 다른 앱에서 보이는 HTML — 상류 라운드 9 백포트 (2026-09-24)
+
+상류가 2026-08-08에 브라우저로 **측정**해서 고친 HTML 결함 중 두 건이 이 포트에 없었다. 둘 다 이 편집기의 HTML
+읽기로는 완벽하게 돌아오므로(자기 출력에 관대하다) 왕복 테스트로는 보이지 않는다.
+
+- **빈 줄이 브라우저에서 보이지 않았다.** 빈 문단(과 빈 목록 항목)을 내용 없는 `<p>`로 써서 높이가 0이었다. 이제
+  `<br/>`을 함께 쓰고, 이 편집기는 표식(`data-are-empty`)이 있으면 그 `<br/>`을 내용으로 읽지 않는다 — 한 줄이
+  두 줄로 불어나지 않는다. 표식 없는 외부 HTML의 빈 요소는 전처럼 버리고, 외부의 `<p><br></p>`은 전처럼 빈 줄이다.
+- **셀 속 그림이 캡션 아래가 아니라 옆에 붙었다.** 셀에 문단 하나와 그림이 있으면 문단을 태그 없이 썼고, `<img>`는
+  인라인이라 글자 줄에 붙었다. 셀에 그림이 있으면 문단을 요소로 쓴다. 문단 하나뿐인 셀은 그대로다.
+
 ### 미게시 변경분 감사 — 결함 3건 (2026-09-24)
 
 1.2.0 이후 들어온 변경을 감사해 찾았다. 셋 다 상류에도 있어 같은 수정을 상류에 옮겼다.

Project_Roadmap.md

@@ -99,8 +99,10 @@ WinUI 3 + Win2D 리치텍스트 에디터. `AvaloniaRichEditor`의 WinUI 포트
   하나(알려진 폴백, 1.2.0과 같음).
 - ~~**실기 확인**~~ → **2026-09-24 사용자 확인, 문제 없음**: 여백 픽커 5단계(레이블·쪽 여백), 쪽 보기의 표 선택
   왼쪽 선·그림 선택 테두리(바깥)·쪽 맨 위 그림 윗선, RTF 저장→열기 뒤 픽커 "보통".
-- **상류와 어긋난 곳(새로 확인)**: 상류는 빈 줄을 HTML로 쓸 때 `<br>`을 넣어 브라우저에서 줄이 보이게 했다(상류 실측)
-  (`HtmlExternalRenderingTests`). 포트는 표식만 써서 **브라우저에서는 빈 줄이 안 보일 수 있다** — 옮길지 측정 후 결정.
+- ~~**상류와 어긋난 곳**~~ → **2026-09-24 옮김**: 상류 라운드 9(2026-08-08)의 HTML 수정 4건 중 포트에 없던 2건 —
+  빈 줄/빈 목록 항목의 `<br/>`(표식이 있으면 읽을 때 버림), 셀에 그림이 있으면 문단을 요소로. 나머지 2건(RTF 가로 병합
+  기하 표기, RTF 용지)은 이미 있었다. `HtmlExternalRenderingTests`(8), 반증 3종, 퍼즈 20,000시드 통과.
+  ⚠ **실기**: 빈 줄을 복사해 Word·HWP에 붙였을 때 한 줄로 들어가는지(두 줄 아님)는 사람이 봐야 한다.
 
 ### 클립보드 경합 재시도 (2026-09-24, PR #55)
 클립보드 기록·관리자가 변경 직후 클립보드를 잠깐 연다(`CLIPBRD_E_CANT_OPEN`). 모든 호출부가 이 오류를 삼켜

src/WinUIRichEditor/Formatters/HtmlDocumentFormatter.cs

@@ -361,7 +361,11 @@ void TakeSpace()
                     pre: name == "pre"); // <pre> keeps its whitespace/newlines verbatim
                 // Empty elements are dropped — foreign HTML uses them for spacing — unless this export
                 // marked one as a blank line the author actually typed (see data-are-empty).
-                if (p.Inlines.Count > 0 || child.GetAttributeValue("data-are-empty", "") == "1")
+                bool markedEmpty = child.GetAttributeValue("data-are-empty", "") == "1";
+                // A marked paragraph carries a <br> so outside renderers give it a line; that <br> is the blank
+                // line's rendering, not its content, and reading it back would turn one blank line into two.
+                if (markedEmpty) p.Inlines.Clear();
+                if (p.Inlines.Count > 0 || markedEmpty)
                     flow.Blocks.Add(p);
             }
             else
@@ -427,10 +431,12 @@ private static void ParseList(HtmlNode listNode, FlowDocument flow, ListKind kin
             ApplyBlockLeafFormat(child, "li", p);
             ParseInlines(child, p, uri: linkUri, inLink: !string.IsNullOrEmpty(linkUri));
             // An empty item is dropped like any empty element — unless our export marked it as a blank item
-            // the author made (data-are-empty, as for paragraphs). Dropped regardless, a blank numbered item
-            // vanished on the first round trip, and the items either side could merge into one list on the
-            // second and lose a marker (fuzz seed 8178, 2026-09-24).
-            if (p.Inlines.Count > 0 || child.GetAttributeValue("data-are-empty", "") == "1") flow.Blocks.Add(p);
+            // the author made (data-are-empty, as for paragraphs), and then its <br> is rendering, not content.
+            // Dropped regardless, a blank numbered item vanished on the first round trip, and the items either
+            // side could merge into one list on the second and lose a marker (fuzz seed 8178, 2026-09-24).
+            bool markedEmpty = child.GetAttributeValue("data-are-empty", "") == "1";
+            if (markedEmpty) p.Inlines.Clear();
+            if (p.Inlines.Count > 0 || markedEmpty) flow.Blocks.Add(p);
 
             // A sublist nested INSIDE the item (the shape most other producers emit) still follows it.
             foreach (var nested in child.ChildNodes.Where(n => n.Name.Equals("ul", StringComparison.OrdinalIgnoreCase) || n.Name.Equals("ol", StringComparison.OrdinalIgnoreCase)))
@@ -1127,6 +1133,12 @@ private static void EmitParagraphElement(StringBuilder sb, Paragraph p, bool new
         // reattachment would otherwise grab whatever paragraph precedes it.
         for (int i = 0; i < p.Inlines.Count; i++)
             EmitInline(sb, p.Inlines[i], i == 0, i == p.Inlines.Count - 1, tag[0] == 'h' ? p.HeadingLevel : 0);
+        // The marker tells only THIS reader about the blank line. An element with no content has zero height, so
+        // in a browser the author's blank line (or blank list item) was invisible — upstream measured the gap
+        // across it as the same 16px as between any two paragraphs (round 9; ported 2026-09-24). The <br> gives it
+        // a line everywhere else — it is what contenteditable editors emit — and the reader drops it when the
+        // marker is present, so one blank line does not become two.
+        if (p.Inlines.Count == 0) sb.Append("<br/>");
         sb.Append($"</{tag}>");
         if (newlineAfter) sb.Append('\n');
     }
@@ -1208,10 +1220,14 @@ private static void EmitTable(StringBuilder sb, TableBlock tb, bool asInline = f
                 // and read those correctly (foreign Word tables with bulleted cells prove it). A lone plain
                 // paragraph keeps the bare form, so the common cell's bytes do not change and the
                 // whitespace rules earned there still stand.
-                bool manyParagraphs = cell.Blocks.Count(b => b is Paragraph) > 1;
+                // An <img> is INLINE, so a bare paragraph followed by a block image in the same cell shared the
+                // image's line — the picture sat beside the caption instead of under it. Counting paragraphs
+                // missed it: the cell has only ONE. <hr> and <table> are block-level and break the line by
+                // themselves, so only an image forces the issue (upstream round 9; ported 2026-09-24).
+                bool needsElementForm = cell.Blocks.Count(b => b is Paragraph) > 1 || cell.Blocks.Any(b => b is ImageBlock);
                 foreach (var cblk in cell.Blocks)
                 {
-                    if (cblk is Paragraph cpara && (manyParagraphs || NeedsOwnElement(cpara)))
+                    if (cblk is Paragraph cpara && (needsElementForm || NeedsOwnElement(cpara)))
                     {
                         if (cpara.IsListItem) cellLists.Sync(cpara.ListType, cpara.ListMarker, cpara.ListLevel);
                         else cellLists.CloseAll();

tests/WinUIRichEditor.Tests/HtmlExternalRenderingTests.cs

@@ -0,0 +1,166 @@
+using System;
+using System.Linq;
+using WinUIRichEditor.Documents;
+using Xunit;
+using WinUIRichEditor.Formatters;
+
+namespace WinUIRichEditor.Tests;
+
+/// <summary>Two HTML defects only an OUTSIDE renderer shows, ported from upstream round 9 (AvaloniaRichEditor
+/// <c>HtmlExternalRenderingTests</c>, 2026-08-08) on 2026-09-24 — the port had neither fix. Both round-trip
+/// through this project's own reader perfectly, because the reader is lenient about exactly what its own writer
+/// emits; upstream found them by measuring the output in a browser. So these assertions read the WRITTEN
+/// MARKUP, not just the model — a symmetry check cannot see a line break that was never written.</summary>
+public class HtmlExternalRenderingTests
+{
+    private static string Text(Paragraph p) => string.Concat(p.Inlines.OfType<Run>().Select(r => r.Text));
+
+    private static FlowDocument Doc(params Block[] blocks)
+    {
+        var doc = new FlowDocument();
+        doc.Blocks.AddRange(blocks);
+        return doc;
+    }
+
+    private static Paragraph P(string? text)
+    {
+        var p = new Paragraph();
+        if (text != null) p.Inlines.Add(new Run { Text = text });
+        return p;
+    }
+
+    // The markup between a marked element's opening and its closing tag.
+    private static string MarkedElement(string html, string closeTag)
+    {
+        int at = html.IndexOf("data-are-empty", StringComparison.Ordinal);
+        Assert.True(at >= 0, "the blank line must still be marked for this reader");
+        return html.Substring(at, html.IndexOf(closeTag, at, StringComparison.Ordinal) - at);
+    }
+
+    // ---- 1. An author's blank line was invisible outside this editor ------------------------------
+
+    // The blank line went out as `<p data-are-empty="1"></p>`. The marker told THIS reader about it, but an
+    // element with no content has zero height, so a browser showed nothing (upstream measured: the gap across
+    // the blank line was the same 16px as between any two paragraphs). The <br> is what gives it a line —
+    // and it has to be INSIDE the marked element, which is what gives that element height.
+    [Fact]
+    public void AnAuthorsBlankLine_IsGivenALineForOutsideRenderers()
+    {
+        string html = HtmlDocumentFormatter.ToHtml(Doc(P("위"), P(null), P("아래")));
+
+        Assert.Contains("<br", MarkedElement(html, "</p>"));
+    }
+
+    // The same for an empty list item: a blank numbered item is a zero-height <li> too.
+    [Fact]
+    public void AnEmptyListItem_IsGivenALineForOutsideRenderers()
+    {
+        var blank = P(null);
+        blank.ListType = ListKind.Ordered;
+        var a = P("a"); a.ListType = ListKind.Ordered;
+        var b = P("b"); b.ListType = ListKind.Ordered;
+
+        string html = HtmlDocumentFormatter.ToHtml(Doc(a, blank, b));
+
+        Assert.Contains("<br", MarkedElement(html, "</li>"));
+    }
+
+    // The <br> is the blank line's rendering, not its content. Read back as content, every save/load turns
+    // one blank line into a line holding a break — two lines. Twice, as round trips are run here.
+    [Fact]
+    public void AnAuthorsBlankLine_DoesNotGrowOnRepeatedRoundTrips()
+    {
+        var once = HtmlDocumentFormatter.ParseHtml(HtmlDocumentFormatter.ToHtml(Doc(P("위"), P(null), P("아래"))));
+        var twice = HtmlDocumentFormatter.ParseHtml(HtmlDocumentFormatter.ToHtml(once));
+
+        foreach (var round in new[] { once, twice })
+        {
+            Assert.Equal(3, round.Blocks.Count);
+            // Not just "no text": a <br> read as content leaves a run holding "\n", which renders as a SECOND
+            // line inside the one blank paragraph.
+            Assert.DoesNotContain(((Paragraph)round.Blocks[1]).Inlines.OfType<Run>(), r => !string.IsNullOrEmpty(r.Text));
+        }
+    }
+
+    // Foreign EMPTY elements keep being dropped — web pages use empty <p>/<div> for spacing, and honouring
+    // them gives every paste that page's vertical rhythm. Only the marker opts in.
+    [Fact]
+    public void AForeignEmptyParagraph_IsStillDropped()
+    {
+        var doc = HtmlDocumentFormatter.ParseHtml("<p>a</p><p></p><p>b</p>");
+
+        Assert.Equal(2, doc.Blocks.Count);
+    }
+
+    // A foreign `<p><br></p>` is NOT empty and never was dropped — it is what contenteditable editors write for
+    // a blank line. It is why the new <br> is safe: a consumer that strips data- attributes still gets the
+    // blank line, and this reader only needs the marker to know the <br> is not content of its own.
+    [Fact]
+    public void AForeignBrOnlyParagraph_IsStillABlankLine()
+    {
+        var doc = HtmlDocumentFormatter.ParseHtml("<p>a</p><p><br></p><p>b</p>");
+
+        Assert.Equal(3, doc.Blocks.Count);
+        Assert.Equal("", Text((Paragraph)doc.Blocks[1]).Trim());
+    }
+
+    // ---- 2. A picture in a cell sat beside the text instead of under it ---------------------------
+
+    private static TableBlock CaptionAndPicture()
+    {
+        var t = new TableBlock(1, 1);
+        var cell = t.Cells[0][0];
+        cell.Blocks.Clear();
+        cell.Blocks.Add(P("캡션"));
+        var pic = new ImageBlock { Width = 80, Height = 50 };
+        pic.SetImageData(OnePixelPng, "image/png");
+        cell.Blocks.Add(pic);
+        return t;
+    }
+
+    private static string CellHtml(string html)
+    {
+        int td = html.IndexOf("<td", StringComparison.Ordinal);
+        return html.Substring(td, html.IndexOf("</td>", td, StringComparison.Ordinal) - td);
+    }
+
+    // A cell's paragraph keeps the bare-inline form when that form can represent it, and the rule counted
+    // PARAGRAPHS. A cell holding one paragraph and a block image has only one, so the paragraph went out bare —
+    // and <img> is inline, so the picture landed on the caption's line. <hr> and <table> are block-level and
+    // break the line themselves; only an image forces this.
+    [Fact]
+    public void APictureInACell_StartsItsOwnLineInsteadOfJoiningTheText()
+    {
+        string cellHtml = CellHtml(HtmlDocumentFormatter.ToHtml(Doc(CaptionAndPicture())));
+
+        Assert.Contains("<p", cellHtml);
+        Assert.True(cellHtml.IndexOf("<p", StringComparison.Ordinal) < cellHtml.IndexOf("<img", StringComparison.Ordinal),
+                    "the caption's element must come before the picture");
+    }
+
+    // The promotion must not change what comes back: still a paragraph and an image, still two blocks.
+    [Fact]
+    public void APictureInACell_StillRoundTripsAsTwoBlocks()
+    {
+        var back = HtmlDocumentFormatter.ParseHtml(HtmlDocumentFormatter.ToHtml(Doc(CaptionAndPicture())));
+        var cell = back.Blocks.OfType<TableBlock>().Single().Cells[0][0];
+
+        Assert.Equal("캡션", Text(cell.Blocks.OfType<Paragraph>().First()));
+        Assert.Single(cell.Blocks.OfType<ImageBlock>());
+    }
+
+    // A plain one-paragraph cell keeps the bare form — the reason the rule exists; the whitespace behaviour
+    // earned there depends on those exact bytes.
+    [Fact]
+    public void APlainCell_KeepsItsBareForm()
+    {
+        var t = new TableBlock(1, 1);
+        t.Cells[0][0].Para.Inlines[0] = new Run { Text = "평문" };
+
+        Assert.DoesNotContain("<p", CellHtml(HtmlDocumentFormatter.ToHtml(Doc(t))));
+    }
+
+    // 1x1 transparent PNG.
+    private static readonly byte[] OnePixelPng = Convert.FromBase64String(
+        "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==");
+}