Use a scoped proj logger to avoid user data lifetime issues (backport)

src/core/proj/qgscoordinatetransform_p.cpp

@@ -244,36 +244,6 @@ void QgsCoordinateTransformPrivate::calculateTransforms( const QgsCoordinateTran
   }
 }
 
-static void proj_collecting_logger( void *user_data, int /*level*/, const char *message )
-{
-  QStringList *dest = reinterpret_cast< QStringList * >( user_data );
-  dest->append( QString( message ) );
-}
-
-static void proj_logger( void *, int level, const char *message )
-{
-#ifndef QGISDEBUG
-  Q_UNUSED( message )
-#endif
-  if ( level == PJ_LOG_ERROR )
-  {
-    const QString messageString( message );
-    if ( messageString == QLatin1String( "push: Invalid latitude" ) )
-    {
-      // these messages tend to spam the console as they can be repeated 1000s of times
-      QgsDebugMsgLevel( messageString, 3 );
-    }
-    else
-    {
-      QgsDebugError( messageString );
-    }
-  }
-  else if ( level == PJ_LOG_DEBUG )
-  {
-    QgsDebugMsgLevel( QString( message ), 3 );
-  }
-}
-
 ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
 {
   QgsReadWriteLocker locker( mProjLock, QgsReadWriteLocker::Read );
@@ -291,8 +261,7 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
   locker.changeMode( QgsReadWriteLocker::Write );
 
   // use a temporary proj error collector
-  QStringList projErrors;
-  proj_log_func( context, &projErrors, proj_collecting_logger );
+  QgsScopedProjCollectingLogger errorLogger;
 
   mIsReversed = false;
 
@@ -342,7 +311,6 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
   {
     if ( !mSourceCRS.projObject() || ! mDestCRS.projObject() )
     {
-      proj_log_func( context, nullptr, nullptr );
       return nullptr;
     }
 
@@ -494,6 +462,7 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
   if ( !transform && nonAvailableError.isEmpty() )
   {
     const int errNo = proj_context_errno( context );
+    const QStringList projErrors = errorLogger.errors();
     if ( errNo && errNo != -61 )
     {
       nonAvailableError = QString( proj_errno_string( errNo ) );
@@ -529,9 +498,6 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
     }
   }
 
-  // reset logger to terminal output
-  proj_log_func( context, nullptr, proj_logger );
-
   if ( !transform )
   {
     // ouch!

src/core/proj/qgsprojutils.cpp

@@ -18,6 +18,7 @@
 #include "qgis.h"
 #include "qgscoordinatetransform.h"
 #include "qgsexception.h"
+#include "qgslogger.h"
 #include <QString>
 #include <QSet>
 #include <QRegularExpression>
@@ -259,6 +260,40 @@ QgsProjUtils::proj_pj_unique_ptr QgsProjUtils::crsToDatumEnsemble( const PJ *crs
 #endif
 }
 
+void QgsProjUtils::proj_collecting_logger( void *user_data, int /*level*/, const char *message )
+{
+  QStringList *dest = reinterpret_cast< QStringList * >( user_data );
+  QString messageString( message );
+  messageString.replace( QLatin1String( "internal_proj_create: " ), QString() );
+  dest->append( messageString );
+}
+
+void QgsProjUtils::proj_logger( void *, int level, const char *message )
+{
+#ifdef QGISDEBUG
+  if ( level == PJ_LOG_ERROR )
+  {
+    const QString messageString( message );
+    if ( messageString == QLatin1String( "push: Invalid latitude" ) )
+    {
+      // these messages tend to spam the console as they can be repeated 1000s of times
+      QgsDebugMsgLevel( messageString, 3 );
+    }
+    else
+    {
+      QgsDebugError( messageString );
+    }
+  }
+  else if ( level == PJ_LOG_DEBUG )
+  {
+    QgsDebugMsgLevel( QString( message ), 3 );
+  }
+#else
+  ( void )level;
+  ( void )message;
+#endif
+}
+
 bool QgsProjUtils::identifyCrs( const PJ *crs, QString &authName, QString &authCode, IdentifyFlags flags )
 {
   authName.clear();
@@ -456,3 +491,18 @@ QStringList QgsProjUtils::searchPaths()
   }
   return res;
 }
+
+//
+// QgsScopedProjCollectingLogger
+//
+
+QgsScopedProjCollectingLogger::QgsScopedProjCollectingLogger()
+{
+  proj_log_func( QgsProjContext::get(), &mProjErrors, QgsProjUtils::proj_collecting_logger );
+}
+
+QgsScopedProjCollectingLogger::~QgsScopedProjCollectingLogger()
+{
+  // reset logger back to terminal output
+  proj_log_func( QgsProjContext::get(), nullptr, QgsProjUtils::proj_logger );
+}

src/core/proj/qgsprojutils.h

@@ -211,6 +211,22 @@ class CORE_EXPORT QgsProjUtils
      */
     static QList< QgsDatumTransform::GridDetails > gridsUsed( const QString &proj );
 
+    /**
+     * Default QGIS proj log function.
+     *
+     * Uses QgsDebugError or QgsDebugMsgLevel to report errors in debug builds only.
+     */
+    static void proj_logger( void *user_data, int level, const char *message );
+
+    /**
+     * QGIS proj log function which collects errors to a QStringList.
+     *
+     * \warning The user_data argument passed to proj_log_func MUST be a QStringList object,
+     * and must exist for the duration where proj_collecting_logger is used. You MUST reset
+     * the proj_log_func to proj_logger before the user data QStringList is destroyed.
+     */
+    static void proj_collecting_logger( void *user_data, int level, const char *message );
+
 #if 0 // not possible in current Proj 6 API
 
     /**
@@ -265,6 +281,46 @@ class CORE_EXPORT QgsProjContext
 #endif
 };
 
+
+/**
+ * \ingroup core
+ *
+ * \brief Scoped object for temporary swapping to an error-collecting PROJ log function.
+ *
+ * Temporarily sets the PROJ log function to one which collects errors for the lifetime of the object,
+ * before returning it to the default QGIS proj logging function on destruction.
+ *
+ * \note The collecting logger ONLY applies to the current thread.
+ *
+ * \note Not available in Python bindings
+ * \since QGIS 3.40
+ */
+class CORE_EXPORT QgsScopedProjCollectingLogger
+{
+  public:
+
+    /**
+     * Constructor for QgsScopedProjCollectingLogger.
+     *
+     * PROJ errors will be collected, and can be retrieved by calling errors().
+     */
+    QgsScopedProjCollectingLogger();
+
+    /**
+     * Returns the PROJ logger back to the default QGIS PROJ logger.
+     */
+    ~QgsScopedProjCollectingLogger();
+
+    /**
+     * Returns the (possibly empty) list of collected errors.
+     */
+    QStringList errors() const { return mProjErrors; }
+
+  private:
+
+    QStringList mProjErrors;
+};
+
 Q_DECLARE_OPERATORS_FOR_FLAGS( QgsProjUtils::IdentifyFlags )
 #endif
 #endif // QGSPROJUTILS_H

src/gui/qgscrsdefinitionwidget.cpp

@@ -110,22 +110,13 @@ void QgsCrsDefinitionWidget::pbnCopyCRS_clicked()
   }
 }
 
-static void proj_collecting_logger( void *user_data, int /*level*/, const char *message )
-{
-  QStringList *dest = reinterpret_cast< QStringList * >( user_data );
-  QString messageString( message );
-  messageString.replace( QLatin1String( "internal_proj_create: " ), QString() );
-  dest->append( messageString );
-}
-
 void QgsCrsDefinitionWidget::validateCurrent()
 {
   const QString projDef = mTextEditParameters->toPlainText();
 
-  PJ_CONTEXT *context = proj_context_create();
+  PJ_CONTEXT *context = QgsProjContext::get();
 
-  QStringList projErrors;
-  proj_log_func( context, &projErrors, proj_collecting_logger );
+  QgsScopedProjCollectingLogger projLogger;
   QgsProjUtils::proj_pj_unique_ptr crs;
 
   switch ( static_cast< Qgis::CrsDefinitionFormat >( mFormatComboBox->currentData().toInt() ) )
@@ -169,16 +160,11 @@ void QgsCrsDefinitionWidget::validateCurrent()
       else
       {
         QMessageBox::warning( this, tr( "Custom Coordinate Reference System" ),
-                              tr( "This proj projection definition is not valid:" ) + QStringLiteral( "\n\n" ) + projErrors.join( '\n' ) );
+                              tr( "This proj projection definition is not valid:" ) + QStringLiteral( "\n\n" ) + projLogger.errors().join( '\n' ) );
       }
       break;
     }
   }
-
-  // reset logger to terminal output
-  proj_log_func( context, nullptr, nullptr );
-  proj_context_destroy( context );
-  context = nullptr;
 }
 
 void QgsCrsDefinitionWidget::formatChanged()