Single parameter version of represent_value

Becuase `represent_value("fieldname")` is much shorter to write and in 98%
there is no need to specify the name separately as
`represent_value("fieldname", 'fieldname')`.

python/core/expression/qgsexpressionfunction.sip

@@ -239,17 +239,18 @@ The help text for the function.
  :rtype: str
 %End
 
-    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) = 0;
+    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) = 0;
 %Docstring
  Returns result of evaluating the function.
  \param values list of values passed to the function
  \param context context expression is being evaluated against
  \param parent parent expression
+ \param node expression node
  :return: result of function
  :rtype: QVariant
 %End
 
-    virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent );
+    virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node );
 %Docstring
  :rtype: QVariant
 %End

python/core/qgsexpressioncontext.sip

@@ -53,7 +53,7 @@ class QgsScopedExpressionFunction : QgsExpressionFunction
 .. versionadded:: 3.0
 %End
 
-    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) = 0;
+    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) = 0;
 
     virtual QgsScopedExpressionFunction *clone() const = 0 /Factory/;
 %Docstring

resources/function_help/json/represent_value

@@ -3,10 +3,11 @@
   "type": "function",
   "description": "Returns the configured representation value for a field value. It depends on the configured widget type. Often, this is useful for 'Value Map' widgets.",
   "arguments": [
-    {"arg":"fieldName", "description": "The field name for which the widget configuration should be loaded."},
-    {"arg":"value", "description": "The value which should be resolved. Most likely a field." }
+    {"arg":"value", "description": "The value which should be resolved. Most likely a field." },
+    {"arg":"fieldName", "description": "The field name for which the widget configuration should be loaded. (Optional)"}
   ],
   "examples": [
-    { "expression":"represent_value('field_with_value_map', \"field_with_value_map\")", "returns":"Description for value"}
+    { "expression":"represent_value(\"field_with_value_map\")", "returns":"Description for value"},
+    { "expression":"represent_value('static value', 'field_name')", "returns":"Description for static value"}
   ]
 }

src/core/expression/qgsexpression.cpp

@@ -240,9 +240,15 @@ bool QgsExpression::isValid() const
   return d->mRootNode;
 }
 
-bool QgsExpression::hasParserError() const { return !d->mParserErrorString.isNull(); }
+bool QgsExpression::hasParserError() const
+{
+  return !d->mParserErrorString.isNull();
+}
 
-QString QgsExpression::parserErrorString() const { return d->mParserErrorString; }
+QString QgsExpression::parserErrorString() const
+{
+  return d->mParserErrorString;
+}
 
 QSet<QString> QgsExpression::referencedColumns() const
 {

src/core/expression/qgsexpressionfunction.h

@@ -40,7 +40,7 @@ class CORE_EXPORT QgsExpressionFunction
 
     /** Function definition for evaluation against an expression context, using a list of values as parameters to the function.
      */
-    typedef QVariant( *FcnEval )( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) SIP_SKIP;
+    typedef QVariant( *FcnEval )( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) SIP_SKIP;
 
     /** \ingroup core
       * Represents a single parameter passed to a function.
@@ -271,11 +271,12 @@ class CORE_EXPORT QgsExpressionFunction
      * \param values list of values passed to the function
      * \param context context expression is being evaluated against
      * \param parent parent expression
+     * \param node expression node
      * \returns result of function
      */
-    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) = 0;
+    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) = 0;
 
-    virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent );
+    virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node );
 
     bool operator==( const QgsExpressionFunction &other ) const;
 
@@ -402,9 +403,9 @@ class QgsStaticExpressionFunction : public QgsExpressionFunction
      * \param parent parent expression
      * \returns result of function
      */
-    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) override
+    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) override
     {
-      return mFnc ? mFnc( values, context, parent ) : QVariant();
+      return mFnc ? mFnc( values, context, parent, node ) : QVariant();
     }
 
     virtual QStringList aliases() const override;
@@ -471,9 +472,9 @@ class QgsWithVariableExpressionFunction : public QgsExpressionFunction
 
     bool isStatic( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const override;
 
-    QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent ) override;
+    QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) override;
 
-    QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) override;
+    QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) override;
 
     bool prepare( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const override;
 

src/core/expression/qgsexpressionnodeimpl.cpp

@@ -846,7 +846,7 @@ QVariant QgsExpressionNodeFunction::evalNode( QgsExpression *parent, const QgsEx
   QString name = QgsExpression::QgsExpression::Functions()[mFnIndex]->name();
   QgsExpressionFunction *fd = context && context->hasFunction( name ) ? context->function( name ) : QgsExpression::QgsExpression::Functions()[mFnIndex];
 
-  QVariant res = fd->run( mArgs, context, parent );
+  QVariant res = fd->run( mArgs, context, parent, this );
   ENSURE_NO_EVAL_ERROR;
 
   // everything went fine

src/core/expression/qgsexpressionnodeimpl.h

@@ -241,7 +241,6 @@ class CORE_EXPORT QgsExpressionNodeFunction : public QgsExpressionNode
   private:
     int mFnIndex;
     NodeList *mArgs = nullptr;
-
 };
 
 /** \ingroup core

src/core/qgsexpressioncontext.cpp

@@ -626,7 +626,7 @@ class GetNamedProjectColor : public QgsScopedExpressionFunction
       }
     }
 
-    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression * ) override
+    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
     {
       QString colorName = values.at( 0 ).toString().toLower();
       if ( mColors.contains( colorName ) )
@@ -657,7 +657,7 @@ class GetComposerItemVariables : public QgsScopedExpressionFunction
       , mComposition( c )
     {}
 
-    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression * ) override
+    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
     {
       if ( !mComposition )
         return QVariant();
@@ -692,7 +692,7 @@ class GetLayerVisibility : public QgsScopedExpressionFunction
       , mLayers( layers )
     {}
 
-    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression * ) override
+    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
     {
       if ( mLayers.isEmpty() )
       {
@@ -729,7 +729,7 @@ class GetProcessingParameterValue : public QgsScopedExpressionFunction
       , mParams( params )
     {}
 
-    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression * ) override
+    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
     {
       return mParams.value( values.at( 0 ).toString() );
     }

src/core/qgsexpressioncontext.h

@@ -91,7 +91,7 @@ class CORE_EXPORT QgsScopedExpressionFunction : public QgsExpressionFunction
       , mReferencedColumns( referencedColumns )
     {}
 
-    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) override = 0;
+    virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node ) override = 0;
 
     /** Returns a clone of the function.
      */

src/providers/virtual/qgsvirtuallayersqlitemodule.cpp

@@ -777,8 +777,8 @@ void qgisFunctionWrapper( sqlite3_context *ctxt, int nArgs, sqlite3_value **args
     };
   }
 
-  QgsExpression parentExpr( QLatin1String( "" ) );
-  QVariant ret = foo->func( variants, &qgisFunctionExpressionContext, &parentExpr );
+  QgsExpression parentExpr = QgsExpression( QString() );
+  QVariant ret = foo->func( variants, &qgisFunctionExpressionContext, &parentExpr, nullptr );
   if ( parentExpr.hasEvalError() )
   {
     QByteArray ba = parentExpr.evalErrorString().toUtf8();

tests/src/core/testqgsexpression.cpp

@@ -386,7 +386,7 @@ class TestQgsExpression: public QObject
 
       // Usage on a value map
       QgsExpressionContext context( QgsExpressionContextUtils::globalProjectLayerScopes( mPointsLayer ) );
-      QgsExpression expression( "represent_value('Pilots', \"Pilots\")" );
+      QgsExpression expression( "represent_value(\"Pilots\", 'Pilots')" );
       if ( expression.hasParserError() )
         qDebug() << expression.parserErrorString();
       Q_ASSERT( !expression.hasParserError() );
@@ -401,7 +401,7 @@ class TestQgsExpression: public QObject
       QCOMPARE( expression.evaluate( &context ).toString(), QStringLiteral( "one" ) );
 
       // Usage on a simple string
-      QgsExpression expression2( "represent_value('Class', \"Class\")" );
+      QgsExpression expression2( "represent_value(\"Class\", 'Class')" );
       if ( expression2.hasParserError() )
         qDebug() << expression2.parserErrorString();
       Q_ASSERT( !expression2.hasParserError() );
@@ -412,6 +412,19 @@ class TestQgsExpression: public QObject
       mPointsLayer->getFeatures( QgsFeatureRequest().setFilterExpression( "Class = 'Jet'" ) ).nextFeature( feature );
       context.setFeature( feature );
       QCOMPARE( expression2.evaluate( &context ).toString(), QStringLiteral( "Jet" ) );
+
+      // Test with implicit field name discovery
+      QgsExpression expression3( "represent_value(\"Pilots\")" );
+      if ( expression3.hasParserError() )
+        qDebug() << expression.parserErrorString();
+      Q_ASSERT( !expression3.hasParserError() );
+      if ( expression3.hasEvalError() )
+        qDebug() << expression3.evalErrorString();
+      Q_ASSERT( !expression3.hasEvalError() );
+      expression3.prepare( &context );
+      mPointsLayer->getFeatures( QgsFeatureRequest().setFilterExpression( "Pilots = 1" ) ).nextFeature( feature );
+      context.setFeature( feature );
+      QCOMPARE( expression.evaluate( &context ).toString(), QStringLiteral( "one" ) );
     }
 
     void evaluation_data()

tests/src/core/testqgsexpressioncontext.cpp

@@ -62,7 +62,7 @@ class TestQgsExpressionContext : public QObject
         GetTestValueFunction()
           : QgsScopedExpressionFunction( QStringLiteral( "get_test_value" ), 1, QStringLiteral( "test" ) ) {}
 
-        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression * ) override
+        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
         {
           return 42;
         }
@@ -80,7 +80,7 @@ class TestQgsExpressionContext : public QObject
         GetTestValueFunction2()
           : QgsScopedExpressionFunction( QStringLiteral( "get_test_value" ), 1, QStringLiteral( "test" ) ) {}
 
-        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression * ) override
+        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
         {
           return 43;
         }
@@ -99,7 +99,7 @@ class TestQgsExpressionContext : public QObject
           , mVal( v )
         {}
 
-        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression * ) override
+        virtual QVariant func( const QVariantList &, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
         {
           if ( !mVal )
             return QVariant();
@@ -228,7 +228,7 @@ void TestQgsExpressionContext::contextScopeFunctions()
   QVERIFY( scope.hasFunction( "get_test_value" ) );
   QVERIFY( scope.function( "get_test_value" ) );
   QgsExpressionContext temp;
-  QCOMPARE( scope.function( "get_test_value" )->func( QVariantList(), &temp, 0 ).toInt(), 42 );
+  QCOMPARE( scope.function( "get_test_value" )->func( QVariantList(), &temp, 0, nullptr ).toInt(), 42 );
 
   //test functionNames
   scope.addFunction( QStringLiteral( "get_test_value2" ), new GetTestValueFunction() );
@@ -371,27 +371,27 @@ void TestQgsExpressionContext::contextStackFunctions()
   QVERIFY( context.hasFunction( "get_test_value" ) );
   QVERIFY( context.function( "get_test_value" ) );
   QgsExpressionContext temp;
-  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0 ).toInt(), 42 );
+  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0, nullptr ).toInt(), 42 );
 
   //add a second scope, should override the first
   context << new QgsExpressionContextScope();
   //test without setting function first...
   QVERIFY( context.hasFunction( "get_test_value" ) );
   QVERIFY( context.function( "get_test_value" ) );
-  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0 ).toInt(), 42 );
+  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0, nullptr ).toInt(), 42 );
 
   //then set the variable so it overrides
   QgsExpressionContextScope *scope2 = context.scope( 1 );
   scope2->addFunction( QStringLiteral( "get_test_value" ), new GetTestValueFunction2() );
   QVERIFY( context.hasFunction( "get_test_value" ) );
   QVERIFY( context.function( "get_test_value" ) );
-  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0 ).toInt(), 43 );
+  QCOMPARE( context.function( "get_test_value" )->func( QVariantList(), &temp, 0, nullptr ).toInt(), 43 );
 
   //make sure stack falls back to earlier contexts
   scope2->addFunction( QStringLiteral( "get_test_value2" ), new GetTestValueFunction() );
   QVERIFY( context.hasFunction( "get_test_value2" ) );
   QVERIFY( context.function( "get_test_value2" ) );
-  QCOMPARE( context.function( "get_test_value2" )->func( QVariantList(), &temp, 0 ).toInt(), 42 );
+  QCOMPARE( context.function( "get_test_value2" )->func( QVariantList(), &temp, 0, nullptr ).toInt(), 42 );
 
   //test functionNames
   QStringList names = context.functionNames();