Fix weird line edit styling error on Ubuntu

Ubuntu theme is incorrectly showing hidden actions in
line edits.

Fixes #18537

(cherry-picked from fb5caa7)

src/gui/qgsfilterlineedit.cpp

@@ -32,20 +32,8 @@ QgsFilterLineEdit::QgsFilterLineEdit( QWidget *parent, const QString &nullValue
   // icon size is about 2/3 height of text, but minimum size of 16
   int iconSize = std::floor( std::max( Qgis::UI_SCALE_FACTOR * fontMetrics().height() * 0.75, 16.0 ) );
 
-  QIcon clearIcon;
-  clearIcon.addPixmap( QgsApplication::getThemeIcon( "/mIconClearText.svg" ).pixmap( QSize( iconSize, iconSize ) ), QIcon::Normal, QIcon::On );
-  clearIcon.addPixmap( QgsApplication::getThemeIcon( "/mIconClearTextHover.svg" ).pixmap( QSize( iconSize, iconSize ) ), QIcon::Selected, QIcon::On );
-  mClearAction = new QAction( clearIcon, QString(), this );
-  mClearAction->setCheckable( false );
-  addAction( mClearAction, QLineEdit::TrailingPosition );
-  connect( mClearAction, &QAction::triggered, this, &QgsFilterLineEdit::clearValue );
-  mClearAction->setVisible( false );
-
-  QIcon searchIcon = QgsApplication::getThemeIcon( "/search.svg" );
-  mSearchAction = new QAction( searchIcon, QString(), this );
-  mSearchAction->setCheckable( false );
-  addAction( mSearchAction, QLineEdit::LeadingPosition );
-  mSearchAction->setVisible( false );
+  mClearIcon.addPixmap( QgsApplication::getThemeIcon( "/mIconClearText.svg" ).pixmap( QSize( iconSize, iconSize ) ), QIcon::Normal, QIcon::On );
+  mClearIcon.addPixmap( QgsApplication::getThemeIcon( "/mIconClearTextHover.svg" ).pixmap( QSize( iconSize, iconSize ) ), QIcon::Selected, QIcon::On );
 
   connect( this, &QLineEdit::textChanged, this,
            &QgsFilterLineEdit::onTextChanged );
@@ -59,13 +47,35 @@ void QgsFilterLineEdit::setShowClearButton( bool visible )
 
 void QgsFilterLineEdit::setShowSearchIcon( bool visible )
 {
-  mSearchIconVisible = visible;
-  mSearchAction->setVisible( visible );
+  if ( visible && !mSearchAction )
+  {
+    QIcon searchIcon = QgsApplication::getThemeIcon( "/search.svg" );
+    mSearchAction = new QAction( searchIcon, QString(), this );
+    mSearchAction->setCheckable( false );
+    addAction( mSearchAction, QLineEdit::LeadingPosition );
+  }
+  else if ( !visible && mSearchAction )
+  {
+    mSearchAction->deleteLater();
+    mSearchAction = nullptr;
+  }
 }
 
 void QgsFilterLineEdit::updateClearIcon()
 {
-  mClearAction->setVisible( shouldShowClear() );
+  bool showClear = shouldShowClear();
+  if ( showClear && !mClearAction )
+  {
+    mClearAction = new QAction( mClearIcon, QString(), this );
+    mClearAction->setCheckable( false );
+    addAction( mClearAction, QLineEdit::TrailingPosition );
+    connect( mClearAction, &QAction::triggered, this, &QgsFilterLineEdit::clearValue );
+  }
+  else if ( !showClear && mClearAction )
+  {
+    mClearAction->deleteLater();
+    mClearAction = nullptr;
+  }
 }
 
 void QgsFilterLineEdit::focusInEvent( QFocusEvent *e )

src/gui/qgsfilterlineedit.h

@@ -19,6 +19,7 @@
 #define QGSFILTERLINEEDIT_H
 
 #include <QLineEdit>
+#include <QIcon>
 #include "qgis.h"
 #include "qgis_gui.h"
 
@@ -64,7 +65,7 @@ class GUI_EXPORT QgsFilterLineEdit : public QLineEdit
       ClearToNull = 0, //!< Reset value to null
       ClearToDefault, //!< Reset value to default value (see defaultValue() )
     };
-    Q_ENUM( ClearMode );
+    Q_ENUM( ClearMode )
 
     /**
      * Constructor for QgsFilterLineEdit.
@@ -133,7 +134,7 @@ class GUI_EXPORT QgsFilterLineEdit : public QLineEdit
      * when no text is entered
      * \since QGIS 3.0
      */
-    bool showSearchIcon() const { return mSearchIconVisible; }
+    bool showSearchIcon() const { return static_cast< bool >( mSearchAction ); }
 
     /**
      * Sets the default value for the widget. The default value is a value
@@ -271,12 +272,12 @@ class GUI_EXPORT QgsFilterLineEdit : public QLineEdit
     void updateClearIcon();
 
   private:
-    QAction *mClearAction;
-    QAction *mSearchAction;
+    QIcon mClearIcon;
+    QAction *mClearAction = nullptr;
+    QAction *mSearchAction = nullptr;
     QAction *mBusySpinnerAction = nullptr;
 
     bool mClearButtonVisible = true;
-    bool mSearchIconVisible = false;
     bool mShowSpinner = false;
 
     ClearMode mClearMode = ClearToNull;