[processing] Fix newlines are stripped from Python traces in log

(cherry-picked from 26bdd92)

Author: nyalldawson

python/gui/processing/qgsprocessingalgorithmdialogbase.sip.in

@@ -215,6 +215,13 @@ Hides the short help panel.
 %Docstring
 Sets the current ``task`` running in the dialog. The task will automatically be started
 by the dialog. Ownership of ``task`` is transferred to the dialog.
+%End
+
+    static QString formatStringForLog( const QString &string );
+%Docstring
+Formats an input ``string`` for display in the log tab.
+
+.. versionadded:: 3.0.1
 %End
 
   protected slots:

src/gui/processing/qgsprocessingalgorithmdialogbase.cpp

@@ -333,21 +333,21 @@ void QgsProcessingAlgorithmDialogBase::pushInfo( const QString &info )
 
 void QgsProcessingAlgorithmDialogBase::pushCommandInfo( const QString &command )
 {
-  txtLog->append( QStringLiteral( "<code>%1<code>" ).arg( command.toHtmlEscaped() ) );
+  txtLog->append( QStringLiteral( "<code>%1<code>" ).arg( formatStringForLog( command.toHtmlEscaped() ) ) );
   scrollToBottomOfLog();
   processEvents();
 }
 
 void QgsProcessingAlgorithmDialogBase::pushDebugInfo( const QString &message )
 {
-  txtLog->append( QStringLiteral( "<span style=\"color:blue\">%1</span>" ).arg( message.toHtmlEscaped() ) );
+  txtLog->append( QStringLiteral( "<span style=\"color:blue\">%1</span>" ).arg( formatStringForLog( message.toHtmlEscaped() ) ) );
   scrollToBottomOfLog();
   processEvents();
 }
 
 void QgsProcessingAlgorithmDialogBase::pushConsoleInfo( const QString &info )
 {
-  txtLog->append( QStringLiteral( "<code><span style=\"color:blue\">%1</darkgray></code>" ).arg( info.toHtmlEscaped() ) );
+  txtLog->append( QStringLiteral( "<code><span style=\"color:blue\">%1</darkgray></code>" ).arg( formatStringForLog( info.toHtmlEscaped() ) ) );
   scrollToBottomOfLog();
   processEvents();
 }
@@ -474,14 +474,21 @@ void QgsProcessingAlgorithmDialogBase::setCurrentTask( QgsProcessingAlgRunnerTas
   QgsApplication::taskManager()->addTask( mAlgorithmTask );
 }
 
+QString QgsProcessingAlgorithmDialogBase::formatStringForLog( const QString &string )
+{
+  QString s = string;
+  s.replace( '\n', QStringLiteral( "<br>" ) );
+  return s;
+}
+
 void QgsProcessingAlgorithmDialogBase::setInfo( const QString &message, bool isError, bool escapeHtml )
 {
   if ( isError )
-    txtLog->append( QStringLiteral( "<span style=\"color:red\">%1</span>" ).arg( message ) );
+    txtLog->append( QStringLiteral( "<span style=\"color:red\">%1</span>" ).arg( formatStringForLog( message ) ) );
   else if ( escapeHtml )
-    txtLog->append( message.toHtmlEscaped() );
+    txtLog->append( formatStringForLog( message.toHtmlEscaped() ) );
   else
-    txtLog->append( message );
+    txtLog->append( formatStringForLog( message ) );
   scrollToBottomOfLog();
   processEvents();
 }

src/gui/processing/qgsprocessingalgorithmdialogbase.h

@@ -260,6 +260,13 @@ class GUI_EXPORT QgsProcessingAlgorithmDialogBase : public QDialog, private Ui::
      */
     void setCurrentTask( QgsProcessingAlgRunnerTask *task SIP_TRANSFER );
 
+    /**
+     * Formats an input \a string for display in the log tab.
+     *
+     * \since QGIS 3.0.1
+     */
+    static QString formatStringForLog( const QString &string );
+
   protected slots:
 
     /**