Add a unit test for use of precalculated static node values in expres…

…sion compilation

tests/src/core/testqgssqliteexpressioncompiler.cpp

@@ -41,6 +41,7 @@ class TestQgsSQLiteExpressionCompiler: public QObject
     void cleanupTestCase();
     void testMakeExpression();
     void testCompiler();
+    void testPreparedCachedNodes();
 
   private:
 
@@ -112,6 +113,31 @@ void TestQgsSQLiteExpressionCompiler::testCompiler()
   QCOMPARE( compiler.result(), QStringLiteral( "lower('a') NOT LIKE lower('A') ESCAPE '\\'" ) );
 }
 
+void TestQgsSQLiteExpressionCompiler::testPreparedCachedNodes()
+{
+  // test that expression compilation of an expression which has precalculated static values for nodes will take advantage of these values
+
+  QgsSQLiteExpressionCompiler compiler = QgsSQLiteExpressionCompiler( mPointsLayer->fields(), false );
+  QgsExpression exp( QStringLiteral( "\"Z\" = (1 + 2) OR \"z\" < (@static_var + 5)" ) );
+
+  QgsExpressionContext context;
+  std::unique_ptr< QgsExpressionContextScope > scope = qgis::make_unique< QgsExpressionContextScope >();
+  scope->setVariable( QStringLiteral( "static_var" ), 10, true );
+  context.appendScope( scope.release() );
+  // not possible to compile due to use of a variable
+  QCOMPARE( compiler.compile( &exp ), QgsSqlExpressionCompiler::Result::Fail );
+
+  // now prepare the expression, so that the static nodes will be precalculated
+  exp.prepare( &context );
+  // should now succeed -- the variable node was identified as a static value and replaced by a pre-computed value
+  QCOMPARE( compiler.compile( &exp ), QgsSqlExpressionCompiler::Result::Complete );
+  QCOMPARE( compiler.result(), QStringLiteral( "((\"Z\" = 3) OR (\"Z\" < 15))" ) );
+
+  // let's try again, denying the compiler the ability to use pre-computed values
+  QgsSQLiteExpressionCompiler compiler2 = QgsSQLiteExpressionCompiler( mPointsLayer->fields(), true );
+  // will fail, because it can't take advantage of the pre-computer variable value and a variable can't be compiled
+  QCOMPARE( compiler2.compile( &exp ), QgsSqlExpressionCompiler::Result::Fail );
+}
 
 
 QGSTEST_MAIN( TestQgsSQLiteExpressionCompiler )