Qt Designer: Adapt style sheet editor colors for dark mode

Add a struct for passing the colors to the CSS highlighter and
populate it in StyleSheetEditor looking at the widget palette.

Fixes: QTCREATORBUG-27087
Change-Id: I1be7616e0e1c3d3898de169fb66c7203c7257523
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
(cherry picked from commit b1b5bc57858a97aa2a4afc6d9b5f9400b0765f50)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 43 insertions, 11 deletions

diff --git a/src/designer/src/lib/shared/csshighlighter.cpp b/src/designer/src/lib/shared/csshighlighter.cpp
index 115b77c17..00d6ab9f2 100644
--- a/src/designer/src/lib/shared/csshighlighter.cpp
+++ b/src/designer/src/lib/shared/csshighlighter.cpp
@@ -32,8 +32,9 @@ QT_BEGIN_NAMESPACE
 
 namespace qdesigner_internal {
 
-CssHighlighter::CssHighlighter(QTextDocument *document)
-: QSyntaxHighlighter(document)
+CssHighlighter::CssHighlighter(const CssHighlightColors &colors,
+                               QTextDocument *document)
+    : QSyntaxHighlighter(document), m_colors(colors)
 {
 }
 
@@ -143,26 +144,26 @@ void CssHighlighter::highlight(const QString &text, int start, int length, int s
 
     switch (state) {
     case Selector:
-        setFormat(start, length, Qt::darkRed);
+        setFormat(start, length, m_colors.selector);
         break;
     case Property:
-        setFormat(start, length, Qt::blue);
+        setFormat(start, length, m_colors.property);
         break;
     case Value:
-        setFormat(start, length, Qt::black);
+        setFormat(start, length, m_colors.value);
         break;
     case Pseudo1:
-        setFormat(start, length, Qt::darkRed);
+        setFormat(start, length, m_colors.pseudo1);
         break;
     case Pseudo2:
-        setFormat(start, length, Qt::darkRed);
+        setFormat(start, length, m_colors.pseudo2);
         break;
     case Quote:
-        setFormat(start, length, Qt::darkMagenta);
+        setFormat(start, length, m_colors.quote);
         break;
     case Comment:
     case MaybeCommentEnd:
-        format.setForeground(Qt::darkGreen);
+        format.setForeground(m_colors.comment);
         setFormat(start, length, format);
         break;
     default:
diff --git a/src/designer/src/lib/shared/csshighlighter_p.h b/src/designer/src/lib/shared/csshighlighter_p.h
index 8af8cd337..0479ba75d 100644
--- a/src/designer/src/lib/shared/csshighlighter_p.h
+++ b/src/designer/src/lib/shared/csshighlighter_p.h
@@ -41,17 +41,30 @@
 #define CSSHIGHLIGHTER_H
 
 #include <QtGui/qsyntaxhighlighter.h>
+#include <QtGui/qcolor.h>
 #include "shared_global_p.h"
 
 QT_BEGIN_NAMESPACE
 
 namespace qdesigner_internal {
 
+struct CssHighlightColors
+{
+    QColor selector;
+    QColor property;
+    QColor value;
+    QColor pseudo1;
+    QColor pseudo2;
+    QColor quote;
+    QColor comment;
+};
+
 class QDESIGNER_SHARED_EXPORT CssHighlighter : public QSyntaxHighlighter
 {
     Q_OBJECT
 public:
-    explicit CssHighlighter(QTextDocument *document);
+    explicit CssHighlighter(const CssHighlightColors &colors,
+                            QTextDocument *document);
 
 protected:
     void highlightBlock(const QString&) override;
@@ -60,6 +73,8 @@ protected:
 private:
     enum State { Selector, Property, Value, Pseudo, Pseudo1, Pseudo2, Quote,
                  MaybeComment, Comment, MaybeCommentEnd };
+
+    const CssHighlightColors m_colors;
 };
 
 } // namespace qdesigner_internal
diff --git a/src/designer/src/lib/shared/stylesheeteditor.cpp b/src/designer/src/lib/shared/stylesheeteditor.cpp
index 2956d1abc..48d38e6a7 100644
--- a/src/designer/src/lib/shared/stylesheeteditor.cpp
+++ b/src/designer/src/lib/shared/stylesheeteditor.cpp
@@ -69,9 +69,25 @@ namespace qdesigner_internal {
 StyleSheetEditor::StyleSheetEditor(QWidget *parent)
     : QTextEdit(parent)
 {
+    enum : int { DarkThreshold = 200 }; // Observed 239 on KDE/Dark
+
     setTabStopDistance(fontMetrics().horizontalAdvance(QLatin1Char(' ')) * 4);
     setAcceptRichText(false);
-    new CssHighlighter(document());
+
+    const QColor textColor = palette().color(QPalette::WindowText);
+    const bool darkMode = textColor.red() > DarkThreshold
+        && textColor.green() > DarkThreshold
+        && textColor.blue() > DarkThreshold;
+
+    CssHighlightColors colors;
+    colors.selector = darkMode ? QColor(Qt::red).lighter() : QColor(Qt::darkRed);
+    const QColor blue(Qt::blue);
+    colors.property = darkMode ? blue.lighter() : blue;
+    colors.pseudo1 = colors.pseudo2 = colors.value = textColor;
+    colors.quote = darkMode ? Qt::magenta : Qt::darkMagenta;
+    colors.comment = darkMode ? Qt::green : Qt::darkGreen;
+
+    new CssHighlighter(colors, document());
 }
 
 // --- StyleSheetEditorDialog