QTextLayout: fix maximumWidth() for a text containing line separator

This is improved version of previous fix
013c346a8dcbd618febb07884c64c740daf9754d that was reverted because it
broke some tests for Quick Text. The problem was that it did not work
correctly in the case the text was wrapped to a fixed width.
To deal with this we'll accumulate current line full width (as if it
hadn't been wrapped) in layout data (layoutData->currentMaxWidth).
Then when the next line is explicitly wrapped by line or paragraph
separator, this accumulated width will be used to adjust layout's
maximum width.

Change-Id: Iad7119d9808e1db15fe1fbc5db049c3db928529f
Fixes: QTBUG-89557
Fixes: QTBUG-104986
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/gui/text/qtextengine.cpp

@@ -2604,6 +2604,7 @@ QTextEngine::LayoutData::LayoutData()
     haveCharAttributes = false;
     logClustersPtr = nullptr;
     available_glyphs = 0;
+    currentMaxWidth = 0;
 }
 
 QTextEngine::LayoutData::LayoutData(const QString &str, void **stack_memory, int _allocated)
@@ -2636,6 +2637,7 @@ QTextEngine::LayoutData::LayoutData(const QString &str, void **stack_memory, int
     hasBidi = false;
     layoutState = LayoutEmpty;
     haveCharAttributes = false;
+    currentMaxWidth = 0;
 }
 
 QTextEngine::LayoutData::~LayoutData()
@@ -2721,6 +2723,7 @@ void QTextEngine::freeMemory()
         layoutData->hasBidi = false;
         layoutData->layoutState = LayoutEmpty;
         layoutData->haveCharAttributes = false;
+        layoutData->currentMaxWidth = 0;
         layoutData->items.clear();
     }
     if (specialData)

src/gui/text/qtextengine_p.h

@@ -385,6 +385,7 @@ public:
         uint layoutState : 2;
         uint memory_on_stack : 1;
         uint haveCharAttributes : 1;
+        QFixed currentMaxWidth;
         QString string;
         bool reallocate(int totalGlyphs);
     };

src/gui/text/qtextlayout.cpp

@@ -1865,6 +1865,7 @@ void QTextLine::layout_helper(int maxGlyphs)
     lbh.logClusters = eng->layoutData->logClustersPtr;
     lbh.previousGlyph = 0;
 
+    bool manuallyWrapped = false;
     bool hasInlineObject = false;
     QFixed maxInlineObjectHeight = 0;
 
@@ -1940,6 +1941,7 @@ void QTextLine::layout_helper(int maxGlyphs)
                 lbh.calculateRightBearingForPreviousGlyph();
             }
             line += lbh.tmpData;
+            manuallyWrapped = true;
             goto found;
         } else if (current.analysis.flags == QScriptAnalysis::Object) {
             lbh.whiteSpaceOrObject = true;
@@ -1974,11 +1976,10 @@ void QTextLine::layout_helper(int maxGlyphs)
                 addNextCluster(lbh.currentPosition, end, lbh.spaceData, lbh.glyphCount,
                                current, lbh.logClusters, lbh.glyphs);
             }
-
-            if (!lbh.manualWrap && lbh.spaceData.textWidth > line.width) {
-                goto found;
-            }
         } else {
+            if (!lbh.manualWrap && lbh.spaceData.textWidth > line.width)
+                goto found;
+
             lbh.whiteSpaceOrObject = false;
             bool sb_or_ws = false;
             lbh.saveCurrentGlyph();
@@ -2161,7 +2162,12 @@ found:
         eng->maxWidth = qMax(eng->maxWidth, line.textWidth);
     } else {
         eng->minWidth = qMax(eng->minWidth, lbh.minw);
-        eng->maxWidth += line.textWidth + lbh.spaceData.textWidth;
+        eng->layoutData->currentMaxWidth += line.textWidth;
+        if (!manuallyWrapped)
+            eng->layoutData->currentMaxWidth += lbh.spaceData.textWidth;
+        eng->maxWidth = qMax(eng->maxWidth, eng->layoutData->currentMaxWidth);
+        if (manuallyWrapped)
+            eng->layoutData->currentMaxWidth = 0;
     }
 
     line.textWidth += trailingSpace;

tests/auto/gui/text/qtextlayout/tst_qtextlayout.cpp

@@ -2655,17 +2655,28 @@ void tst_QTextLayout::min_maximumWidth_data()
     QTest::newRow("long string") << QStringLiteral("lmong_long_crazy_87235982735_23857239682376923876923876-fuwhfhfw-names-AAAA-deeaois2019-03-03.and.more");
     QTest::newRow("QTBUG-106947") << QStringLiteral("text                                text");
     QTest::newRow("spaces") << QStringLiteral("                text                text                ");
+    QTest::newRow("QTBUG-104986") << QStringLiteral("text\ntext\ntext");
+    QTest::newRow("spaces + line breaks") << QStringLiteral("       \n         text\n                \ntext       \n         ");
 }
 
 void tst_QTextLayout::min_maximumWidth()
 {
     QFETCH(QString, text);
+    text.replace('\n', QChar::LineSeparator);
 
     QTextLayout layout(text, testFont);
     layout.setCacheEnabled(true);
 
-    for (int wrapMode = QTextOption::NoWrap; wrapMode <= QTextOption::WrapAtWordBoundaryOrAnywhere; ++wrapMode) {
     QTextOption opt;
+    opt.setWrapMode(QTextOption::NoWrap);
+    layout.setTextOption(opt);
+    layout.beginLayout();
+    while (layout.createLine().isValid()) { }
+    layout.endLayout();
+
+    const qreal nonWrappedMaxWidth = layout.maximumWidth();
+
+    for (int wrapMode = QTextOption::NoWrap; wrapMode <= QTextOption::WrapAtWordBoundaryOrAnywhere; ++wrapMode) {
         opt.setWrapMode((QTextOption::WrapMode)wrapMode);
         layout.setTextOption(opt);
         layout.beginLayout();
@@ -2674,6 +2685,9 @@ void tst_QTextLayout::min_maximumWidth()
         const qreal minWidth = layout.minimumWidth();
         const qreal maxWidth = layout.maximumWidth();
 
+        QCOMPARE_LE(minWidth, maxWidth);
+        QCOMPARE_LE(maxWidth, nonWrappedMaxWidth); // maxWidth for wrapped text shouldn't exceed maxWidth for the text without wrapping.
+
         // Try the layout from slightly wider than the widest (maxWidth)
         // and narrow it down to slighly narrower than minWidth
         // layout.maximumWidth() should return the same regardless