Add implementation of the REGEXP operator

When not configured otherwise in the Preferences Dialog register a
SQLite function for performing the regular expression matching which
SQLite doesn't implement. This adds support for the REGEXP operator even
when no extension which implements this is loaded.

See issue #215.

src/PreferencesDialog.cpp

@@ -72,6 +72,7 @@ void PreferencesDialog::loadSettings()
     ui->spinLogFontSize->setValue(getSettingsValue("log", "fontsize").toInt());
 
     ui->listExtensions->addItems(getSettingsValue("extensions", "list").toStringList());
+    ui->checkRegexDisabled->setChecked(getSettingsValue("extensions", "disableregex").toBool());
     fillLanguageBox();
 }
 
@@ -100,6 +101,7 @@ void PreferencesDialog::saveSettings()
     foreach(QListWidgetItem* item, ui->listExtensions->findItems(QString("*"), Qt::MatchWrap | Qt::MatchWildcard))
         extList.append(item->text());
     setSettingsValue("extensions", "list", extList);
+    setSettingsValue("extensions", "disableregex", ui->checkRegexDisabled->isChecked());
 
     // Warn about restarting to change language
     QVariant newLanguage = ui->languageComboBox->itemData(ui->languageComboBox->currentIndex());
@@ -233,6 +235,10 @@ QVariant PreferencesDialog::getSettingsDefaultValue(const QString& group, const
     if(group == "extensions" && name == "list")
         return QStringList();
 
+    // extensions/disableregex?
+    if(group == "extension" && name == "disableregex")
+        return false;
+
     // Unknown combination of group and name? Return an invalid QVariant!
     return QVariant();
 }

src/PreferencesDialog.ui

@@ -498,6 +498,16 @@
          </item>
         </layout>
        </item>
+       <item>
+        <widget class="QCheckBox" name="checkRegexDisabled">
+         <property name="toolTip">
+          <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;While supporting the REGEXP operator SQLite doesn't implement any regular expression&lt;br/&gt;algorithm but calls back the running application. DB Browser for SQLite implements this&lt;br/&gt;algorithm for you to let you use REGEXP out of the box. However, as there are multiple possible&lt;br/&gt;implementations of this and you might want to use another one, you're free to disable the&lt;br/&gt;application's implementation and load your own by using an extension. Requires restart of the application.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+         </property>
+         <property name="text">
+          <string>Disable Regular Expression extension</string>
+         </property>
+        </widget>
+       </item>
       </layout>
      </widget>
     </widget>

src/sqlitedb.cpp

@@ -35,6 +35,26 @@ void collation_needed(void* /*pData*/, sqlite3* db, int eTextRep, const char* sC
         sqlite3_create_collation(db, sCollationName, eTextRep, NULL, collCompare);
 }
 
+
+static void regexp(sqlite3_context* ctx, int /*argc*/, sqlite3_value* argv[])
+{
+    // Get arguments and check their values
+    QRegExp arg1((const char*)sqlite3_value_text(argv[0]));
+    QString arg2((const char*)sqlite3_value_text(argv[1]));
+    if(!arg1.isValid() || arg2.isNull())
+        return sqlite3_result_error(ctx, "invalid operand", -1);
+
+    // Set the pattern matching syntax to a Perl-like one. This is the default in Qt 4.x but Qt 5
+    // changes this to a greedy one (QRegExp::RegExp2). To make sure the behaviour of our application
+    // doesn't change depending on the build environment, we make sure to always set the same pattern
+    // matching syntax.
+    arg1.setPatternSyntax(QRegExp::RegExp);
+
+    // Perform the actual matching and return the result. Note that Qt's QRegExp returns -1 if the regex
+    // doesn't match and the position in the string otherwise; SQLite expects a 0 for not found and a 1 for found.
+    sqlite3_result_int(ctx, arg1.indexIn(arg2) >= 0);
+}
+
 bool DBBrowserDB::isOpen ( ) const
 {
     return _db!=0;
@@ -93,6 +113,10 @@ bool DBBrowserDB::open(const QString& db)
         // Enable extension loading
         sqlite3_enable_load_extension(_db, 1);
 
+        // Register REGEXP function
+        if(settings.value("/extensions/disableregex", false) == false)
+            sqlite3_create_function(_db, "REGEXP", 2, SQLITE_UTF8, NULL, regexp, NULL, NULL);
+
         curDBFilename = db;
         return true;
     } else {