Allow setting expression format help string for QgsExpressionLineEdit

python/gui/auto_generated/qgsexpressionbuilderdialog.sip.in

@@ -37,22 +37,19 @@ The builder widget that is used by the dialog
 
     QString expectedOutputFormat();
 %Docstring
-The set expected format string. This is pure text format and no expression validation
+Returns the expected format string, which is shown in the dialog.
+This is purely a text format and no expression validation
 is done against it.
 
-:return: The expected value format.
+.. seealso:: :py:func:`setExpectedOutputFormat`
 %End
 
     void setExpectedOutputFormat( const QString &expected );
 %Docstring
-The set expected format string. This is pure text format and no expression validation
+Set the ``expected`` format string, which is shown in the dialog.
-is done against it.
+This is purely a text format and no expression validation is done against it.
 
-:param expected: The expected value format for the expression.
+.. seealso:: :py:func:`expectedOutputFormat`
-
-.. note::
-
-   Only a UI hint and not used for expression validation.
 %End
 
     QgsExpressionContext expressionContext() const;

python/gui/auto_generated/qgsexpressionlineedit.sip.in

@@ -63,6 +63,27 @@ Sets whether the widget should show a multiline text editor.
                   to show single line editor (the default).
 %End
 
+    QString expectedOutputFormat() const;
+%Docstring
+Returns the expected format string, which is shown in the expression builder dialog for the widget.
+This is purely a text format and no expression validation
+is done against it.
+
+.. seealso:: :py:func:`setExpectedOutputFormat`
+
+.. versionadded:: 3.4
+%End
+
+    void setExpectedOutputFormat( const QString &expected );
+%Docstring
+Set the ``expected`` format string, which is shown in the expression builder dialog for the widget.
+This is purely a text format and no expression validation is done against it.
+
+.. seealso:: :py:func:`expectedOutputFormat`
+
+.. versionadded:: 3.4
+%End
+
     void setGeomCalculator( const QgsDistanceArea &distanceArea );
 %Docstring
 Set the geometry calculator used in the expression dialog.

src/gui/qgsexpressionbuilderdialog.h

@@ -48,17 +48,17 @@ class GUI_EXPORT QgsExpressionBuilderDialog : public QDialog, private Ui::QgsExp
     QString expressionText();
 
     /**
-     * The set expected format string. This is pure text format and no expression validation
+     * Returns the expected format string, which is shown in the dialog.
+     * This is purely a text format and no expression validation
      * is done against it.
-     * \returns The expected value format.
+     * \see setExpectedOutputFormat()
      */
     QString expectedOutputFormat();
 
     /**
-     * The set expected format string. This is pure text format and no expression validation
+     * Set the \a expected format string, which is shown in the dialog.
-     * is done against it.
+     * This is purely a text format and no expression validation is done against it.
-     * \param expected The expected value format for the expression.
+     * \see expectedOutputFormat()
-     * \note Only a UI hint and not used for expression validation.
      */
     void setExpectedOutputFormat( const QString &expected );
 

src/gui/qgsexpressionlineedit.cpp

@@ -103,6 +103,16 @@ void QgsExpressionLineEdit::setMultiLine( bool multiLine )
   }
 }
 
+QString QgsExpressionLineEdit::expectedOutputFormat() const
+{
+  return mExpectedOutputFormat;
+}
+
+void QgsExpressionLineEdit::setExpectedOutputFormat( const QString &expected )
+{
+  mExpectedOutputFormat = expected;
+}
+
 void QgsExpressionLineEdit::setGeomCalculator( const QgsDistanceArea &da )
 {
   mDa.reset( new QgsDistanceArea( da ) );
@@ -151,6 +161,7 @@ void QgsExpressionLineEdit::editExpression()
   QgsExpressionContext context = mExpressionContextGenerator ? mExpressionContextGenerator->createExpressionContext() : mExpressionContext;
 
   QgsExpressionBuilderDialog dlg( mLayer, currentExpression, this, QStringLiteral( "generic" ), context );
+  dlg.setExpectedOutputFormat( mExpectedOutputFormat );
   if ( mDa )
   {
     dlg.setGeomCalculator( *mDa );

src/gui/qgsexpressionlineedit.h

@@ -78,6 +78,23 @@ class GUI_EXPORT QgsExpressionLineEdit : public QWidget
      */
     void setMultiLine( bool multiLine );
 
+    /**
+     * Returns the expected format string, which is shown in the expression builder dialog for the widget.
+     * This is purely a text format and no expression validation
+     * is done against it.
+     * \see setExpectedOutputFormat()
+     * \since QGIS 3.4
+     */
+    QString expectedOutputFormat() const;
+
+    /**
+     * Set the \a expected format string, which is shown in the expression builder dialog for the widget.
+     * This is purely a text format and no expression validation is done against it.
+     * \see expectedOutputFormat()
+     * \since QGIS 3.4
+     */
+    void setExpectedOutputFormat( const QString &expected );
+
     /**
      * Set the geometry calculator used in the expression dialog.
      * \param distanceArea calculator
@@ -160,6 +177,7 @@ class GUI_EXPORT QgsExpressionLineEdit : public QWidget
     QgsExpressionContext mExpressionContext;
     const QgsExpressionContextGenerator *mExpressionContextGenerator = nullptr;
     QgsVectorLayer *mLayer = nullptr;
+    QString mExpectedOutputFormat;
 
     bool isExpressionValid( const QString &expressionStr );