MDEV-35739 ST_INTERSECTION precise self-intersection

ST_INTERSECTION(geom_1, geom_1) returns geom_1 exactly.

Replaces 'goto exit;' in Item_func_spatial_operation::val_str with SCOPE_EXIT.
This was done to leverage existing geometry construction calls without
incurring compiler errors caused by skipping initialization on goto.

mysql-test/main/gis.result

@@ -5507,3 +5507,24 @@ ST_SRID(g1)	ST_SRID(ST_GeomFromWKB(g1, 4326))	ST_SRID(ST_GeomFromWKB(g1))	ST_AsT
 SELECT ST_DISTANCE_SPHERE(st_geomfromtext('linestring( 2 2, 2 8) '), ST_GeomFromText('POINT(18.413076 43.856258)')) ;
 ERROR HY000: Calling geometry function st_distance_sphere with unsupported types of arguments.
 # End of 10.5 tests
+#
+# Start of 10.11 tests
+#
+#
+# MDEV-35739 Linestring self-intersection equality
+#
+CREATE TABLE t1(geom geometry NOT NULL);
+INSERT INTO t1 (geom) VALUES(ST_GeomFromText('LINESTRING(2 2,4 4,6 2,3 2,2 4)'));
+SELECT ST_ASTEXT(geom) FROM t1;
+ST_ASTEXT(geom)
+LINESTRING(2 2,4 4,6 2,3 2,2 4)
+SELECT ST_EQUALS(geom, ST_INTERSECTION(geom, geom)) AS isequal, ST_ASTEXT(ST_INTERSECTION(geom, geom)) AS intersection FROM t1;
+isequal	intersection
+1	LINESTRING(2 2,4 4,6 2,3 2,2 4)
+SELECT ST_AsText(ST_SYMDIFFERENCE(geom, ST_Intersection(geom, geom))) FROM t1;
+ST_AsText(ST_SYMDIFFERENCE(geom, ST_Intersection(geom, geom)))
+GEOMETRYCOLLECTION EMPTY
+DROP TABLE t1;
+#
+# End of 10.11 tests
+#

mysql-test/main/gis.test

@@ -3515,3 +3515,21 @@ FROM (
 SELECT ST_DISTANCE_SPHERE(st_geomfromtext('linestring( 2 2, 2 8) '), ST_GeomFromText('POINT(18.413076 43.856258)')) ;
 
 --echo # End of 10.5 tests
+
+--echo #
+--echo # Start of 10.11 tests
+--echo #
+
+--echo #
+--echo # MDEV-35739 Linestring self-intersection equality
+--echo #
+CREATE TABLE t1(geom geometry NOT NULL);
+INSERT INTO t1 (geom) VALUES(ST_GeomFromText('LINESTRING(2 2,4 4,6 2,3 2,2 4)'));
+SELECT ST_ASTEXT(geom) FROM t1;
+SELECT ST_EQUALS(geom, ST_INTERSECTION(geom, geom)) AS isequal, ST_ASTEXT(ST_INTERSECTION(geom, geom)) AS intersection FROM t1;
+SELECT ST_AsText(ST_SYMDIFFERENCE(geom, ST_Intersection(geom, geom))) FROM t1;
+DROP TABLE t1;
+
+--echo #
+--echo # End of 10.11 tests
+--echo #

sql/item_geofunc.cc

@@ -1547,6 +1547,12 @@ String *Item_func_spatial_operation::val_str(String *str_value)
 {
   DBUG_ENTER("Item_func_spatial_operation::val_str");
   DBUG_ASSERT(fixed());
+  SCOPE_EXIT([this] () {
+    collector.reset();
+    func.reset();
+    res_receiver.reset();
+  });
+
   Geometry_ptr_with_buffer_and_mbr g1, g2;
   uint32 srid= 0;
   Gcalc_operation_transporter trn(&func, &collector);
@@ -1559,7 +1565,23 @@ String *Item_func_spatial_operation::val_str(String *str_value)
                     g2.construct(args[1], &tmp_value2))))
   {
     str_value= 0;
-    goto exit;
+    DBUG_RETURN(str_value);
+  }
+
+  /*
+    Optimization to evaluate the particular self-intersection
+      ST_INTERSECTION(geom, geom);
+  */
+  if (spatial_op == Gcalc_function::op_type::op_intersection &&
+      *g1.geom == *g2.geom)
+  {
+    /*
+      Return either argument as the result, it doesn't matter which because
+      they're identical.
+    */
+    String *sres= args[0]->val_str(&tmp_value1);  // tmp_value1 is empty...
+    str_value->swap(*sres);  // ...so swap the val_str result with str_value...
+    DBUG_RETURN(str_value);  // ...to create a valid query result.
   }
 
   g1.mbr.add_mbr(&g2.mbr);
@@ -1568,33 +1590,29 @@ String *Item_func_spatial_operation::val_str(String *str_value)
   if ((null_value= g1.store_shapes(&trn) || g2.store_shapes(&trn)))
   {
     str_value= 0;
-    goto exit;
+    DBUG_RETURN(str_value);
   }
 
   collector.prepare_operation();
   if (func.alloc_states())
-    goto exit;
+    DBUG_RETURN(str_value);
 
   operation.init(&func);
 
   if (operation.count_all(&collector) ||
       operation.get_result(&res_receiver))
-    goto exit;
+    DBUG_RETURN(str_value);
 
 
   str_value->set_charset(&my_charset_bin);
   str_value->length(0);
   if (str_value->reserve(SRID_SIZE, 512))
-    goto exit;
+    DBUG_RETURN(str_value);
   str_value->q_append(srid);
 
   if (!Geometry::create_from_opresult(&g1.buffer, str_value, res_receiver))
-    goto exit;
+    DBUG_RETURN(str_value);
 
-exit:
-  collector.reset();
-  func.reset();
-  res_receiver.reset();
   DBUG_RETURN(str_value);
 }
 

sql/spatial.cc

@@ -424,6 +424,28 @@ int Geometry::bbox_as_json(String *wkt)
 }
 
 
+/**
+ * Geometry::operator==
+ *
+ * @param rhs   a Geometry instance to compare to *this
+ * @return true when *this is the same Geometry as rhs, false otherwise.  If
+ *              either *this or rhs have no Geometry associated (because, for
+ *              example, they are built with the default constructor) then the
+ *              comparison will always be false.
+ */
+bool Geometry::operator==(Geometry &rhs) const
+{
+  if (!m_data || !rhs.m_data)
+    return false;
+
+  const ptrdiff_t len= m_data_end - m_data;
+  if (len != rhs.m_data_end - rhs.m_data)
+    return false;
+
+  return memcmp(m_data, rhs.m_data, len) == 0;
+}
+
+
 static double wkb_get_double(const char *ptr, Geometry::wkbByteOrder bo)
 {
   double res;

sql/spatial.h

@@ -384,6 +384,8 @@ public:
             (expected_points > ((m_data_end - data) /
                                 (POINT_DATA_SIZE + extra_point_space))));
   }
+
+  bool operator==(Geometry &rhs) const;
 protected:
   const char *m_data;
   const char *m_data_end;