Avoid ending Markdown fenced code blocks with gratuitous blank lines

This caused unnecessary empty <pre> blocks when converting markdown to
HTML, made code blocks too large using QSyntaxHighlighter to highlight
the whole block, and caused assymmetry when rewriting markdown.

Pick-to: 6.3
Fixes: QTBUG-101031
Change-Id: I08016577ccb92edb4afae31d7df3259cb011d5c8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/gui/text/qtextmarkdownimporter.cpp

@@ -498,6 +498,14 @@ int QTextMarkdownImporter::cbText(int textType, const char *text, unsigned size)
     case MD_BLOCK_TD:
         m_nonEmptyTableCells.append(m_tableCol);
         break;
+    case MD_BLOCK_CODE:
+        if (s == Newline) {
+            // defer a blank line until we see something else in the code block,
+            // to avoid ending every code block with a gratuitous blank line
+            m_needsInsertBlock = true;
+            s = QString();
+        }
+        break;
     default:
         break;
     }
@@ -531,12 +539,12 @@ int QTextMarkdownImporter::cbText(int textType, const char *text, unsigned size)
                     QString::number(bfmt.intProperty(QTextFormat::BlockQuoteLevel));
         if (bfmt.hasProperty(QTextFormat::BlockCodeLanguage))
             debugInfo += "in a code block"_L1;
+        if (m_cursor->currentList())
+            debugInfo += "in a list"_L1;
         qCDebug(lcMD) << textType << "in block" << m_blockType << s << qPrintable(debugInfo)
                       << "bindent" << bfmt.indent() << "tindent" << bfmt.textIndent()
                       << "margins" << bfmt.leftMargin() << bfmt.topMargin() << bfmt.bottomMargin() << bfmt.rightMargin();
     }
-    qCDebug(lcMD) << textType << "in block" << m_blockType << s << "in list?" << m_cursor->currentList()
-                  << "indent" << m_cursor->blockFormat().indent();
     return 0; // no error
 }
 

src/gui/text/qtextmarkdownwriter.cpp

@@ -156,11 +156,11 @@ void QTextMarkdownWriter::writeFrame(const QTextFrame *frame)
                 for (int col = cell.column(); col < spanEndCol; ++col)
                     m_stream << "|";
             } else if (m_fencedCodeBlock && ending) {
-                m_stream << m_linePrefix << QString(m_wrappedLineIndent, Space)
+                m_stream << Newline << m_linePrefix << QString(m_wrappedLineIndent, Space)
                          << m_codeBlockFence << Newline << Newline;
                 m_codeBlockFence.clear();
             } else if (m_indentedCodeBlock && nextIsDifferent) {
-                m_stream << Newline;
+                m_stream << Newline << Newline;
             } else if (endingCol > 0) {
                 if (block.textList() || block.blockFormat().hasProperty(QTextFormat::BlockCodeLanguage)) {
                     m_stream << Newline;

tests/auto/gui/text/qtextmarkdownimporter/tst_qtextmarkdownimporter.cpp

@@ -380,7 +380,7 @@ void tst_QTextMarkdownImporter::avoidBlankLineAtBeginning_data()
 
     QTest::newRow("Text block") << QString("Markdown text") << 1;
     QTest::newRow("Headline") << QString("Markdown text\n============") << 1;
-    QTest::newRow("Code block") << QString("    Markdown text") << 2;
+    QTest::newRow("Code block") << QString("    Markdown text") << 1;
     QTest::newRow("Unordered list") << QString("* Markdown text") << 1;
     QTest::newRow("Ordered list") << QString("1. Markdown text") << 1;
     QTest::newRow("Blockquote") << QString("> Markdown text") << 1;
@@ -501,18 +501,17 @@ void tst_QTextMarkdownImporter::fencedCodeBlocks_data()
     QTest::addColumn<QString>("expectedFenceChar");
     QTest::addColumn<QString>("rewrite");
 
-    // TODO shouldn't add empty blocks: QTBUG-101031
     QTest::newRow("backtick fence with language")
             << "```pseudocode\nprint('hello world\\n')\n```\n"
-            << 2 << 0 << "pseudocode" << "`"
+            << 1 << 0 << "pseudocode" << "`"
             << "```pseudocode\nprint('hello world\\n')\n```\n\n";
     QTest::newRow("tilde fence with language")
             << "~~~pseudocode\nprint('hello world\\n')\n~~~\n"
-            << 2 << 0 << "pseudocode" << "~"
+            << 1 << 0 << "pseudocode" << "~"
             << "~~~pseudocode\nprint('hello world\\n')\n~~~\n\n";
     QTest::newRow("embedded backticks")
             << "```\nnone `one` ``two``\n```\nplain\n```\n```three``` ````four````\n```\nplain\n"
-            << 4 << 2 << QString() << "`"
+            << 2 << 2 << QString() << "`"
             << "```\nnone `one` ``two``\n```\nplain\n\n```\n```three``` ````four````\n```\nplain\n\n";
 }
 

tests/auto/gui/text/qtextmarkdownwriter/data/blockquotes.md

@@ -50,6 +50,7 @@ Now let's have an indented code block:
     }
 
 and end with a fenced code block:
+
 ~~~pseudocode
 #include <something.h>
 #include <else.h>

tests/auto/gui/text/qtextmarkdownwriter/tst_qtextmarkdownwriter.cpp

@@ -494,7 +494,7 @@ void tst_QTextMarkdownWriter::fromHtml_data()
         "![foo](/url \"title\")\n\n";
     QTest::newRow("code") <<
         "<pre class=\"language-pseudocode\">\n#include \"foo.h\"\n\nblock {\n    statement();\n}\n\n</pre>" <<
-        "```pseudocode\n#include \"foo.h\"\n\nblock {\n    statement();\n}\n```\n\n";
+        "```pseudocode\n#include \"foo.h\"\n\nblock {\n    statement();\n}\n\n```\n\n";
     // TODO
 //    QTest::newRow("escaped number and paren after double newline") <<
 //        "<p>(The first sentence of this paragraph is a line, the next paragraph has a number</p>13) but that's not part of an ordered list" <<