Feature/variables optimization (#673)

* Added optimization to FOR loops by disabling allocation if RETURN statement returns NONE

* Added support of ignoring expression results in variable declaration using '_' as a variable name

pkg/compiler/compiler_for_test.go

@@ -45,6 +45,23 @@ func TestFor(t *testing.T) {
 		So(string(out), ShouldEqual, "[1,2,3]")
 	})
 
+	Convey("Should not allocate memory if NONE is a return statement", t, func() {
+		c := compiler.New()
+
+		p, err := c.Compile(`
+			FOR i IN 0..100
+				RETURN NONE
+		`)
+
+		So(err, ShouldBeNil)
+		So(p, ShouldHaveSameTypeAs, &runtime.Program{})
+
+		out, err := p.Run(context.Background())
+
+		So(err, ShouldBeNil)
+		So(string(out), ShouldEqual, "[]")
+	})
+
 	Convey("Should compile FOR i, k IN [1, 2, 3] RETURN k", t, func() {
 		c := compiler.New()
 

pkg/compiler/compiler_let_test.go

@@ -337,4 +337,41 @@ func TestLet(t *testing.T) {
 		So(err, ShouldBeNil)
 		So(string(out), ShouldEqual, `false`)
 	})
+
+	Convey("Should use ignorable variable name", t, func() {
+		out, err := newCompilerWithObservable().MustCompile(`
+			LET _ = (FOR i IN 1..100 RETURN NONE)
+
+			RETURN TRUE
+		`).Run(context.Background())
+
+		So(err, ShouldBeNil)
+		So(string(out), ShouldEqual, `true`)
+	})
+
+	Convey("Should allow to declare a variable name using _", t, func() {
+		c := compiler.New()
+
+		out, err := c.MustCompile(`
+			LET _ = (FOR i IN 1..100 RETURN NONE)
+			LET _ = (FOR i IN 1..100 RETURN NONE)
+
+			RETURN TRUE
+		`).Run(context.Background())
+
+		So(err, ShouldBeNil)
+		So(string(out), ShouldEqual, `true`)
+	})
+
+	Convey("Should not allow to use ignorable variable name", t, func() {
+		c := compiler.New()
+
+		_, err := c.Compile(`
+			LET _ = (FOR i IN 1..100 RETURN NONE)
+
+			RETURN _
+		`)
+
+		So(err, ShouldNotBeNil)
+	})
 }

pkg/compiler/scope.go

@@ -55,6 +55,10 @@ func (s *scope) HasVariable(name string) bool {
 }
 
 func (s *scope) SetVariable(name string) error {
+	if name == core.IgnorableVariable {
+		return nil
+	}
+
 	_, exists := s.vars[name]
 
 	if exists {

pkg/compiler/visitor.go

@@ -249,6 +249,7 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 	if !isWhileLoop {
 		srcCtx := ctx.ForExpressionSource().(*fql.ForExpressionSourceContext)
 		srcExp, err := v.doVisitForExpressionSource(srcCtx, scope)
+
 		if err != nil {
 			return nil, err
 		}
@@ -266,6 +267,7 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 	} else {
 		whileExpCtx := ctx.Expression().(*fql.ExpressionContext)
 		conditionExp, err := v.doVisitExpression(whileExpCtx, scope)
+
 		if err != nil {
 			return nil, err
 		}
@@ -315,6 +317,7 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 				valVarName,
 				keyVarName,
 			)
+
 			if err != nil {
 				return nil, err
 			}
@@ -325,6 +328,7 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 				statementCtx.(*fql.ForExpressionStatementContext),
 				forInScope,
 			)
+
 			if err != nil {
 				return nil, err
 			}
@@ -336,12 +340,14 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 	var spread bool
 	var distinct bool
 	var predicate core.Expression
+	var passThrough bool
 	forRetCtx := ctx.ForExpressionReturn().(*fql.ForExpressionReturnContext)
 	returnCtx := forRetCtx.ReturnExpression()
 
 	if returnCtx != nil {
 		returnCtx := returnCtx.(*fql.ReturnExpressionContext)
 		returnExp, err := v.doVisitReturnExpression(returnCtx, forInScope)
+
 		if err != nil {
 			return nil, err
 		}
@@ -353,9 +359,13 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 		}
 
 		predicate = returnExp
+
+		ret := returnExp.(*expressions.ReturnExpression)
+		passThrough = literals.IsNone(ret.Predicate())
 	} else {
 		forInCtx := forRetCtx.ForExpression().(*fql.ForExpressionContext)
 		forInExp, err := v.doVisitForExpression(forInCtx, forInScope)
+
 		if err != nil {
 			return nil, err
 		}
@@ -371,7 +381,9 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 		predicate,
 		distinct,
 		spread,
+		passThrough,
 	)
+
 	if err != nil {
 		return nil, err
 	}
@@ -1130,8 +1142,12 @@ func (v *visitor) doVisitVariable(ctx *fql.VariableContext, scope *scope) (core.
 func (v *visitor) doVisitVariableDeclaration(ctx *fql.VariableDeclarationContext, scope *scope) (core.Expression, error) {
 	var init core.Expression
 	var err error
+	name := core.IgnorableVariable
+
+	if id := ctx.Identifier(); id != nil {
+		name = id.GetText()
+	}
 
-	name := ctx.Identifier().GetText()
 	err = scope.SetVariable(name)
 
 	if err != nil {

pkg/parser/antlr/FqlLexer.g4

@@ -86,6 +86,7 @@ While: 'WHILE';
 // Literals
 Param: '@';
 Identifier: Letter+ (Symbols (Identifier)*)* (Digit (Identifier)*)*;
+IgnoreIdentifier: Underscore;
 StringLiteral: SQString | DQSring | BacktickString | TickString;
 IntegerLiteral: [0-9]+;
 FloatLiteral
@@ -111,7 +112,8 @@ fragment ExponentPart
 fragment Letter
     : 'A'..'Z' | 'a'..'z'
     ;
-fragment Symbols: '_';
+fragment Symbols: Underscore;
+fragment Underscore: '_';
 fragment Digit
     : '0'..'9'
     ;

pkg/parser/antlr/FqlLexer.tokens

@@ -62,11 +62,12 @@ Do=61
 While=62
 Param=63
 Identifier=64
-StringLiteral=65
-IntegerLiteral=66
-FloatLiteral=67
-NamespaceSegment=68
-UnknownIdentifier=69
+IgnoreIdentifier=65
+StringLiteral=66
+IntegerLiteral=67
+FloatLiteral=68
+NamespaceSegment=69
+UnknownIdentifier=70
 ':'=5
 ';'=6
 '.'=7

pkg/parser/antlr/FqlParser.g4

@@ -41,6 +41,7 @@ bodyExpression
 
 variableDeclaration
     : Let Identifier Assign expression
+    | Let IgnoreIdentifier Assign expression
     ;
 
 returnExpression

pkg/parser/fql/FqlLexer.tokens

@@ -62,11 +62,12 @@ Do=61
 While=62
 Param=63
 Identifier=64
-StringLiteral=65
-IntegerLiteral=66
-FloatLiteral=67
-NamespaceSegment=68
-UnknownIdentifier=69
+IgnoreIdentifier=65
+StringLiteral=66
+IntegerLiteral=67
+FloatLiteral=68
+NamespaceSegment=69
+UnknownIdentifier=70
 ':'=5
 ';'=6
 '.'=7

pkg/parser/fql/FqlParser.tokens

@@ -62,11 +62,12 @@ Do=61
 While=62
 Param=63
 Identifier=64
-StringLiteral=65
-IntegerLiteral=66
-FloatLiteral=67
-NamespaceSegment=68
-UnknownIdentifier=69
+IgnoreIdentifier=65
+StringLiteral=66
+IntegerLiteral=67
+FloatLiteral=68
+NamespaceSegment=69
+UnknownIdentifier=70
 ':'=5
 ';'=6
 '.'=7