Add left,right,rpad,lpad string functions - Fix #6079

    - With tests :)

Author: NathanW2

resources/function_help/left-en_US

@@ -0,0 +1,15 @@
+<h3>left() function</h3>
+Returns a substring that contains the <i>n</i> leftmost characters of the string.
+
+<h4>Syntax</h4>
+<code>left(string, pos)</code><br>
+
+<h4>Arguments</h4>
+<code>string</code> - is string. The string.
+<br>
+<code>length</code> - is int. The numbder of characters from the left to return.
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>left('Hello World',5) -> 'Hello'</code><br>
+

resources/function_help/lpad-en_US

@@ -0,0 +1,17 @@
+<h3>lpad() function</h3>
+Returns a string with supplied width padded
+using the fill character.
+
+<h4>Syntax</h4>
+<code>lpad(string, width, fill)</code><br>
+
+<h4>Arguments</h4>
+<code>string</code> - is string. The string.
+<br>
+<code>width</code> - is int. The length of the new string.
+<br>
+<code>fill</code> - is char. The character to padd the remaining space with. 
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>lpad('Hello', 10, 'x') -> 'Helloxxxxx'</code><br>

resources/function_help/right-en_US

@@ -0,0 +1,15 @@
+<h3>right() function</h3>
+Returns a substring that contains the <i>n</i> rightmost characters of the string.
+
+<h4>Syntax</h4>
+<code>right(string, pos)</code><br>
+
+<h4>Arguments</h4>
+<code>string</code> - is string. The string.
+<br>
+<code>length</code> - is int. The numbder of characters from the right to return.
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>right('Hello World',5) -> 'World'</code><br>
+

resources/function_help/rpad-en_US

@@ -0,0 +1,18 @@
+<h3>rpad() function</h3>
+Returns a string with supplied width padded
+using the fill character.
+
+<h4>Syntax</h4>
+<code>rpad(string, width, fill)</code><br>
+
+<h4>Arguments</h4>
+<code>string</code> - is string. The string.
+<br>
+<code>width</code> - is int. The length of the new string.
+<br>
+<code>fill</code> - is char. The character to padd the remaining space with. 
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>rpad('Hello', 10, 'x') -> 'xxxxxHello'</code><br>
+

src/core/qgsexpression.cpp

@@ -511,6 +511,36 @@ static QVariant fcnStrpos( const QVariantList& values, QgsFeature* , QgsExpressi
   return string.indexOf( QRegExp( getStringValue( values.at( 1 ), parent ) ) );
 }
 
+static QVariant fcnRight( const QVariantList& values, QgsFeature* , QgsExpression *parent )
+{
+  QString string = getStringValue( values.at( 0 ), parent );
+  int pos = getIntValue( values.at( 1 ), parent );
+  return string.right( pos );
+}
+
+static QVariant fcnLeft( const QVariantList& values, QgsFeature* , QgsExpression *parent )
+{
+  QString string = getStringValue( values.at( 0 ), parent );
+  int pos = getIntValue( values.at( 1 ), parent );
+  return string.left( pos );
+}
+
+static QVariant fcnRPad( const QVariantList& values, QgsFeature* , QgsExpression *parent )
+{
+  QString string = getStringValue( values.at( 0 ), parent );
+  int length = getIntValue( values.at( 1 ), parent );
+  QString fill = getStringValue( values.at( 2 ), parent );
+  return string.rightJustified( length, fill.at( 0 ), true );
+}
+
+static QVariant fcnLPad( const QVariantList& values, QgsFeature* , QgsExpression *parent )
+{
+  QString string = getStringValue( values.at( 0 ), parent );
+  int length = getIntValue( values.at( 1 ), parent );
+  QString fill = getStringValue( values.at( 2 ), parent );
+  return string.leftJustified( length, fill.at( 0 ), true );
+}
+
 static QVariant fcnNow( const QVariantList&, QgsFeature* , QgsExpression * )
 {
   return QVariant( QDateTime::currentDateTime() );
@@ -775,6 +805,11 @@ const QList<QgsExpression::FunctionDef> &QgsExpression::BuiltinFunctions()
     << FunctionDef( "substr", 3, fcnSubstr, QObject::tr( "String" ) )
     << FunctionDef( "concat", -1, fcnConcat, QObject::tr( "String" ) )
     << FunctionDef( "strpos", 2, fcnStrpos, QObject::tr( "String" ) )
+    << FunctionDef( "left", 2, fcnLeft, QObject::tr( "String" ) )
+    << FunctionDef( "right", 2, fcnRight, QObject::tr( "String" ) )
+    << FunctionDef( "rpad", 3, fcnRPad, QObject::tr( "String" ) )
+    << FunctionDef( "lpad", 3, fcnLPad, QObject::tr( "String" ) )
+
     // geometry accessors
     << FunctionDef( "xat", 1, fcnXat, QObject::tr( "Geometry" ), "", true )
     << FunctionDef( "yat", 1, fcnYat, QObject::tr( "Geometry" ), "", true )

tests/src/core/testqgsexpression.cpp

@@ -257,6 +257,12 @@ class TestQgsExpression: public QObject
       QTest::newRow( "substr outside" ) << "substr('HeLLo', -5,2)" << false << QVariant( "" );
       QTest::newRow( "strpos" ) << "strpos('Hello World','World')" << false << QVariant( 6 );
       QTest::newRow( "strpos outside" ) << "strpos('Hello World','blah')" << false << QVariant( -1 );
+      QTest::newRow( "left" ) << "left('Hello World',5)" << false << QVariant( "Hello" );
+      QTest::newRow( "right" ) << "right('Hello World', 5)" << false << QVariant( "World" );
+      QTest::newRow( "rpad" ) << "rpad('Hello', 10, 'x')" << false << QVariant( "xxxxxHello" );
+      QTest::newRow( "rpad truncate" ) << "rpad('Hello', 4, 'x')" << false << QVariant( "Hell" );
+      QTest::newRow( "lpad" ) << "lpad('Hello', 10, 'x')" << false << QVariant( "Helloxxxxx" );
+      QTest::newRow( "lpad truncate" ) << "rpad('Hello', 4, 'x')" << false << QVariant( "Hell" );
 
       // implicit conversions
       QTest::newRow( "implicit int->text" ) << "length(123)" << false << QVariant( 3 );