Add trim function

resources/function_help/trim-en_US

@@ -0,0 +1,13 @@
+<h3>trim() function</h3>
+Removes all leading and trailing whitespace (spaces, tabs, etc) from a string.
+
+<p><h4>Syntax</h4>
+     trim(<i>string</i>)</p>
+
+<p><h4>Arguments</h4>
+<!-- List args for functions here-->
+<i>  string</i> &rarr; is string. The string to trim.</p>
+
+<p><h4>Example</h4>
+<!-- Show example of function.-->
+     trim('   hello world    ') &rarr; 'hello world'</p>

src/core/qgsexpression.cpp

@@ -536,6 +536,13 @@ static QVariant fcnTitle( const QVariantList& values, QgsFeature* , QgsExpressio
   }
   return QVariant( elems.join( " " ) );
 }
+
+static QVariant fcnTrim( const QVariantList& values, QgsFeature* , QgsExpression* parent )
+{
+  QString str = getStringValue( values.at( 0 ), parent );
+  return QVariant( str.trimmed() );
+}
+
 static QVariant fcnLength( const QVariantList& values, QgsFeature* , QgsExpression* parent )
 {
   QString str = getStringValue( values.at( 0 ), parent );
@@ -1316,7 +1323,8 @@ const QStringList &QgsExpression::BuiltinFunctions()
     << "coalesce" << "regexp_match" << "$now" << "age" << "year"
     << "month" << "week" << "day" << "hour"
     << "minute" << "second" << "lower" << "upper"
-    << "title" << "length" << "replace" << "regexp_replace" << "regexp_substr"
+    << "title" << "length" << "replace" << "trim"
+    << "regexp_replace" << "regexp_substr"
     << "substr" << "concat" << "strpos" << "left"
     << "right" << "rpad" << "lpad"
     << "format_number" << "format_date"
@@ -1379,6 +1387,7 @@ const QList<QgsExpression::Function*> &QgsExpression::Functions()
     << new StaticFunction( "lower", 1, fcnLower, QObject::tr( "String" ) )
     << new StaticFunction( "upper", 1, fcnUpper, QObject::tr( "String" ) )
     << new StaticFunction( "title", 1, fcnTitle, QObject::tr( "String" ) )
+    << new StaticFunction( "trim", 1, fcnTrim, QObject::tr( "String" ) )
     << new StaticFunction( "length", 1, fcnLength, QObject::tr( "String" ) )
     << new StaticFunction( "replace", 3, fcnReplace, QObject::tr( "String" ) )
     << new StaticFunction( "regexp_replace", 3, fcnRegexpReplace, QObject::tr( "String" ) )

tests/src/core/testqgsexpression.cpp

@@ -296,6 +296,8 @@ class TestQgsExpression: public QObject
       QTest::newRow( "lpad" ) << "lpad('Hello', 10, 'x')" << false << QVariant( "Helloxxxxx" );
       QTest::newRow( "lpad truncate" ) << "rpad('Hello', 4, 'x')" << false << QVariant( "Hell" );
       QTest::newRow( "title" ) << "title(' HeLlO   WORLD ')" << false << QVariant( " Hello   World " );
+      QTest::newRow( "trim" ) << "trim('   Test String ')" << false << QVariant( "Test String" );
+      QTest::newRow( "trim empty string" ) << "trim('')" << false << QVariant( "" );
       QTest::newRow( "format" ) << "format('%1 %2 %3 %1', 'One', 'Two', 'Three')" << false << QVariant( "One Two Three One" );
 
       // implicit conversions