Cache validity check results

For non-point geometry subclasses (points are always valid!) we
now cache the results of a geometry validity check. Subsequent
checks utilise the cached result wherever possible.

Because QgsGeometry/QgsFeature objects are implicitly shared, this
means that we avoid a *lot* of duplicate validity checks as
features and geometries are thrown around during processing model
execution.

Author: nyalldawson

python/core/auto_generated/geometry/qgsabstractgeometry.sip.in

@@ -607,6 +607,20 @@ Converts the geometry to a specified type.
 .. versionadded:: 2.14
 %End
 
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const = 0;
+%Docstring
+Checks validity of the geometry, and returns ``True`` if the geometry is valid.
+
+:param flags: indicates optional flags which control the type of validity checking performed
+              (corresponding to QgsGeometry.ValidityFlags).
+
+:return: - ``True`` if geometry is valid
+         - error: will be set to the validity error message
+
+
+.. versionadded:: 3.8
+%End
+
 
     QgsGeometryPartIterator parts();
 %Docstring

python/core/auto_generated/geometry/qgscurve.sip.in

@@ -172,6 +172,8 @@ Returns a geometry without curves. Caller takes ownership
 
     virtual QgsRectangle boundingBox() const;
 
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const;
+
 
     virtual double xAt( int index ) const = 0;
 %Docstring

python/core/auto_generated/geometry/qgsgeometrycollection.sip.in

@@ -206,6 +206,8 @@ Returns a geometry without curves. Caller takes ownership
 
     virtual QgsPoint vertexAt( QgsVertexId id ) const;
 
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const;
+
 
     virtual bool addZValue( double zValue = 0 );
 

python/core/auto_generated/geometry/qgsmultipoint.sip.in

@@ -50,6 +50,8 @@ Multi point geometry collection.
 
     virtual double segmentLength( QgsVertexId startVertex ) const;
 
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const;
+
 
 
     virtual QgsMultiPoint *createEmptyWithSameType() const /Factory/;

python/core/auto_generated/geometry/qgspoint.sip.in

@@ -371,6 +371,8 @@ M value is preserved.
 
     virtual QgsAbstractGeometry *boundary() const /Factory/;
 
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const;
+
 
     virtual bool insertVertex( QgsVertexId position, const QgsPoint &vertex );
 

python/core/auto_generated/geometry/qgssurface.sip.in

@@ -25,14 +25,16 @@ Ownership is transferred to the caller.
 %End
 
     virtual QgsRectangle boundingBox() const;
-%Docstring
-Returns the minimal bounding box for the geometry
-%End
+
+    virtual bool isValid( QString &error /Out/, int flags = 0 ) const;
+
+
 
   protected:
 
     virtual void clearCache() const;
 
+
 };
 
 /************************************************************************

src/core/geometry/qgsabstractgeometry.h

@@ -577,6 +577,19 @@ class CORE_EXPORT QgsAbstractGeometry
      */
     virtual bool convertTo( QgsWkbTypes::Type type );
 
+    /**
+     * Checks validity of the geometry, and returns TRUE if the geometry is valid.
+     *
+     * \param error will be set to the validity error message
+     * \param flags indicates optional flags which control the type of validity checking performed
+     * (corresponding to QgsGeometry::ValidityFlags).
+     *
+     * \returns TRUE if geometry is valid
+     *
+     * \since QGIS 3.8
+     */
+    virtual bool isValid( QString &error SIP_OUT, int flags = 0 ) const = 0;
+
 #ifndef SIP_RUN
 
     /**

src/core/geometry/qgscurve.cpp

@@ -21,6 +21,7 @@
 #include "qgslinestring.h"
 #include "qgspoint.h"
 #include "qgsmultipoint.h"
+#include "qgsgeos.h"
 
 bool QgsCurve::operator==( const QgsAbstractGeometry &other ) const
 {
@@ -188,6 +189,25 @@ QgsRectangle QgsCurve::boundingBox() const
   return mBoundingBox;
 }
 
+bool QgsCurve::isValid( QString &error, int flags ) const
+{
+  if ( flags == 0 && mHasCachedValidity )
+  {
+    // use cached validity results
+    error = mValidityFailureReason;
+    return error.isEmpty();
+  }
+
+  QgsGeos geos( this );
+  bool res = geos.isValid( &error, flags & QgsGeometry::FlagAllowSelfTouchingHoles, nullptr );
+  if ( flags == 0 )
+  {
+    mValidityFailureReason = !res ? error : QString();
+    mHasCachedValidity = true;
+  }
+  return res;
+}
+
 QPolygonF QgsCurve::asQPolygonF() const
 {
   const int nb = numPoints();
@@ -224,6 +244,8 @@ QgsCurve::Orientation QgsCurve::orientation() const
 void QgsCurve::clearCache() const
 {
   mBoundingBox = QgsRectangle();
+  mHasCachedValidity = false;
+  mValidityFailureReason.clear();
   QgsAbstractGeometry::clearCache();
 }
 

src/core/geometry/qgscurve.h

@@ -162,6 +162,7 @@ class CORE_EXPORT QgsCurve: public QgsAbstractGeometry
     QgsCurve *toCurveType() const override SIP_FACTORY;
 
     QgsRectangle boundingBox() const override;
+    bool isValid( QString &error SIP_OUT, int flags = 0 ) const override;
 
     /**
      * Returns the x-coordinate of the specified node in the line string.
@@ -290,6 +291,9 @@ class CORE_EXPORT QgsCurve: public QgsAbstractGeometry
   private:
 
     mutable QgsRectangle mBoundingBox;
+
+    mutable bool mHasCachedValidity = false;
+    mutable QString mValidityFailureReason;
 };
 
 #endif // QGSCURVE_H

src/core/geometry/qgsgeometry.cpp

@@ -2504,15 +2504,7 @@ bool QgsGeometry::isGeosValid( const QgsGeometry::ValidityFlags flags ) const
     return false;
   }
 
-  // avoid calling geos for trivial point geometries
-  if ( QgsWkbTypes::geometryType( d->geometry->wkbType() ) == QgsWkbTypes::PointGeometry )
-  {
-    return true;
-  }
-
-  QgsGeos geos( d->geometry.get() );
-  mLastError.clear();
-  return geos.isValid( &mLastError, flags & FlagAllowSelfTouchingHoles, nullptr );
+  return d->geometry->isValid( mLastError, static_cast< int >( flags ) );
 }
 
 bool QgsGeometry::isSimple() const