Proper symlink handling for layers and projects

- Prevent QGIS from silently resolving symlinks in qgspathresolver.cpp
- Respect symlink for “%_attachments.zip” companion file in .qgs project
- Add new tests to verify good behaviours in common symlink scenarios
- Fix formatting

Fixes #60135

src/core/qgsarchive.cpp

@@ -76,9 +76,18 @@ bool QgsArchive::zip( const QString &filename )
     return false;
   }
 
+  QString target {filename};
+
   // remove existing zip file
-  if ( QFile::exists( filename ) )
-    QFile::remove( filename );
+  if ( QFile::exists( target ) )
+  {
+    // If symlink -> we want to write to its target instead
+    const QFileInfo targetFileInfo( target );
+    target = targetFileInfo.canonicalFilePath();
+    // If target still exists, remove (might not exist if was a dangling symlink)
+    if ( QFile::exists( target ) )
+      QFile::remove( target );
+  }
 
 #ifdef Q_OS_WIN
   // Clear temporary flag (see GH #32118)
@@ -94,9 +103,9 @@ bool QgsArchive::zip( const QString &filename )
 #endif // Q_OS_WIN
 
   // save zip archive
-  if ( ! tmpFile.rename( filename ) )
+  if ( ! tmpFile.rename( target ) )
   {
-    const QString err = QObject::tr( "Unable to save zip file '%1'" ).arg( filename );
+    const QString err = QObject::tr( "Unable to save zip file '%1'" ).arg( target );
     QgsMessageLog::logMessage( err, QStringLiteral( "QgsArchive" ) );
     return false;
   }

src/core/qgspathresolver.cpp

@@ -130,7 +130,7 @@ QString QgsPathResolver::readPath( const QString &f ) const
     }
     else
     {
-      return vsiPrefix + fi.canonicalFilePath();
+      return vsiPrefix + QDir::cleanPath( fi.absoluteFilePath() );
     }
   }
 
@@ -291,7 +291,8 @@ QString QgsPathResolver::writePath( const QString &s ) const
 
   const QFileInfo srcFileInfo( srcPath );
   if ( srcFileInfo.exists() )
-    srcPath = srcFileInfo.canonicalFilePath();
+    // Do NOT resolve symlinks, but do remove '..' and '.'
+    srcPath = QDir::cleanPath( srcFileInfo.absoluteFilePath() );
 
   // if this is a VSIFILE, remove the VSI prefix and append to final result
   const QString vsiPrefix = QgsGdalUtils::vsiPrefixForPath( src );