Respect choice of relative or absolute paths for virtual layers when saving project.

Fixes #29481

Author: jdugge

src/core/qgsvectorlayer.cpp

@@ -78,6 +78,7 @@
 #include "qgsvectorlayerrenderer.h"
 #include "qgsvectorlayerundocommand.h"
 #include "qgsvectorlayerfeaturecounter.h"
+#include "qgsvirtuallayerdefinition.h"
 #include "qgspoint.h"
 #include "qgsrenderer.h"
 #include "qgssymbollayer.h"
@@ -1833,6 +1834,37 @@ QString QgsVectorLayer::encodedSource( const QString &source, const QgsReadWrite
     // Refetch the source from the provider, because adding fields actually changes the source for this provider.
     src = dataProvider()->dataSourceUri();
   }
+  else if ( providerType() == QLatin1String( "virtual" ) )
+  {
+    QUrl urlSource = QUrl::fromEncoded( src.toLatin1() );
+    QUrl url = QUrl::fromEncoded( src.toLatin1() );
+    QUrl urlSourceLayer;
+    QStringList theURIParts;
+
+    QUrlQuery query = QUrlQuery( urlSource.query() );
+    QList<QPair<QString, QString> > queryItems = query.queryItems();
+
+    for ( int i = 0; i < queryItems.size(); i++ )
+    {
+      QString key = queryItems.at( i ).first;
+      QString value = queryItems.at( i ).second;
+      if ( key == QLatin1String( "layer" ) )
+      {
+        // syntax: provider:url_encoded_source_URI(:name(:encoding)?)?
+        theURIParts = value.split( ':' );
+        theURIParts[1] = QUrl::fromPercentEncoding( theURIParts[1].toUtf8() );
+        theURIParts[1] = context.pathResolver().writePath( theURIParts[1] );
+        theURIParts[1] = QUrl::toPercentEncoding( theURIParts[1] );
+        queryItems[i].second =  theURIParts.join( QStringLiteral( ":" ) ) ;
+      }
+    }
+
+    query.setQueryItems( queryItems );
+
+    QUrl urlDest = QUrl( urlSource );
+    urlDest.setQuery( query.query() );
+    src = QString::fromLatin1( urlDest.toEncoded() );
+  }
   else
   {
     src = context.pathResolver().writePath( src );
@@ -1878,6 +1910,37 @@ QString QgsVectorLayer::decodedSource( const QString &source, const QString &pro
     urlDest.setQueryItems( urlSource.queryItems() );
     src = QString::fromLatin1( urlDest.toEncoded() );
   }
+  else if ( provider == QLatin1String( "virtual" ) )
+  {
+    QUrl urlSource = QUrl::fromEncoded( src.toLatin1() );
+    QUrl url = QUrl::fromEncoded( src.toLatin1() );
+    QUrl urlSourceLayer;
+    QStringList theURIParts;
+
+    QUrlQuery query = QUrlQuery( urlSource.query() );
+    QList<QPair<QString, QString> > queryItems = query.queryItems();
+
+    for ( int i = 0; i < queryItems.size(); i++ )
+    {
+      QString key = queryItems.at( i ).first;
+      QString value = queryItems.at( i ).second;
+      if ( key == QLatin1String( "layer" ) )
+      {
+        // syntax: provider:url_encoded_source_URI(:name(:encoding)?)?
+        theURIParts = value.split( ':' );
+        theURIParts[1] = QUrl::fromPercentEncoding( theURIParts[1].toUtf8() );
+        theURIParts[1] = context.pathResolver().readPath( theURIParts[1] );
+        theURIParts[1] = QUrl::toPercentEncoding( theURIParts[1] );
+        queryItems[i].second =  theURIParts.join( QStringLiteral( ":" ) ) ;
+      }
+    }
+
+    query.setQueryItems( queryItems );
+
+    QUrl urlDest = QUrl( urlSource );
+    urlDest.setQuery( query.query() );
+    src = QString::fromLatin1( urlDest.toEncoded() );
+  }
   else
   {
     src = context.pathResolver().readPath( src );