Excel export returns a zero bytes file when system temp not writable MDL-7176

lib/excellib.class.php

@@ -46,10 +46,14 @@ class MoodleExcelWorkbook {
      * @param string $filename The name of the file
      */
     function MoodleExcelWorkbook($filename) {
+        global $CFG;
     /// Internally, create one PEAR Spreadsheet_Excel_Writer_Workbook class
         $this->pear_excel_workbook = new Spreadsheet_Excel_Writer($filename);
     /// Prepare it to accept UTF-16LE data and to encode it properly
         $this->pear_excel_workbook->setVersion(8);
+    /// Choose our temporary directory, because default system tmp might not be writable - see MDL-7176, found by paulo.matos
+        make_upload_directory('temp/excel', false);
+        $this->pear_excel_workbook->setTempDir($CFG->dataroot.'/temp/excel');
     }
 
     /* Create one Moodle Worksheet