feat: add support for fill modifiers in binary operations

binary_op.go

@@ -123,6 +123,16 @@ func isBinaryOpBoolModifier(s string) bool {
 	return s == "bool"
 }
 
+func isBinaryOpFillModifier(s string) bool {
+	s = strings.ToLower(s)
+	switch s {
+	case "fill", "fill_left", "fill_right":
+		return true
+	default:
+		return false
+	}
+}
+
 // IsBinaryOpCmp returns true if op is comparison operator such as '==', '!=', etc.
 func IsBinaryOpCmp(op string) bool {
 	switch op {

parser.go

@@ -402,6 +402,15 @@ func (p *parser) parseExpr() (Expr, error) {
 				}
 			}
 		}
+		for {
+			ok, err := p.parseFillModifier(&be)
+			if err != nil {
+				return nil, err
+			}
+			if !ok {
+				break
+			}
+		}
 		e2, err := p.parseSingleExpr()
 		if err != nil {
 			return nil, err
@@ -506,6 +515,62 @@ func (p *parser) parseSingleExprWithoutRollupSuffix() (Expr, error) {
 	}
 }
 
+func (p *parser) parseFillModifier(be *BinaryOpExpr) (bool, error) {
+	if !isBinaryOpFillModifier(p.lex.Token) {
+		return false, nil
+	}
+	op := strings.ToLower(p.lex.Token)
+	if err := p.lex.Next(); err != nil {
+		return false, err
+	}
+	if p.lex.Token != "(" {
+		p.lex.Prev()
+		return false, nil
+	}
+	if err := p.lex.Next(); err != nil {
+		return false, err
+	}
+	ne, err := p.parseFillValue()
+	if err != nil {
+		return false, fmt.Errorf("cannot parse %s fill value: %w", op, err)
+	}
+	if p.lex.Token != ")" {
+		return false, fmt.Errorf(`%s: unexpected token %q; want ")"`, op, p.lex.Token)
+	}
+	if err := p.lex.Next(); err != nil {
+		return false, err
+	}
+	switch op {
+	case "fill":
+		be.FillLeft = ne
+		be.FillRight = ne
+	case "fill_left":
+		be.FillLeft = ne
+	case "fill_right":
+		be.FillRight = ne
+	}
+	return true, nil
+}
+
+func (p *parser) parseFillValue() (*NumberExpr, error) {
+	neg := false
+	if p.lex.Token == "-" {
+		neg = true
+		if err := p.lex.Next(); err != nil {
+			return nil, err
+		}
+	}
+	ne, err := p.parsePositiveNumberExpr()
+	if err != nil {
+		return nil, err
+	}
+	if neg {
+		ne.N = -ne.N
+		ne.s = "-" + ne.s
+	}
+	return ne, nil
+}
+
 func (p *parser) parsePositiveNumberExpr() (*NumberExpr, error) {
 	if !isPositiveNumberPrefix(p.lex.Token) && !isInfOrNaN(p.lex.Token) {
 		return nil, fmt.Errorf(`positiveNumberExpr: unexpected token %q; want "number"`, p.lex.Token)
@@ -1896,6 +1961,12 @@ type BinaryOpExpr struct {
 	// If KeepMetricNames is set to true, then the operation should keep metric names.
 	KeepMetricNames bool
 
+	// FillLeft contains the fill value for fill_left() or fill() modifier.
+	FillLeft *NumberExpr
+
+	// FillRight contains the fill value for fill_right() or fill() modifier.
+	FillRight *NumberExpr
+
 	// Left contains left arg for the `left op right` expression.
 	Left Expr
 
@@ -1971,6 +2042,22 @@ func (be *BinaryOpExpr) appendModifiers(dst []byte) []byte {
 			dst = prefix.AppendString(dst)
 		}
 	}
+	if be.FillLeft != nil && be.FillLeft == be.FillRight {
+		dst = append(dst, " fill("...)
+		dst = be.FillLeft.AppendString(dst)
+		dst = append(dst, ')')
+	} else {
+		if be.FillLeft != nil {
+			dst = append(dst, " fill_left("...)
+			dst = be.FillLeft.AppendString(dst)
+			dst = append(dst, ')')
+		}
+		if be.FillRight != nil {
+			dst = append(dst, " fill_right("...)
+			dst = be.FillRight.AppendString(dst)
+			dst = append(dst, ')')
+		}
+	}
 	return dst
 }
 
@@ -1989,7 +2076,7 @@ func needBinaryOpArgParens(arg Expr) bool {
 }
 
 func isReservedBinaryOpIdent(s string) bool {
-	return isBinaryOpGroupModifier(s) || isBinaryOpJoinModifier(s) || isBinaryOpBoolModifier(s) || isPrefixModifier(s)
+	return isBinaryOpGroupModifier(s) || isBinaryOpJoinModifier(s) || isBinaryOpBoolModifier(s) || isPrefixModifier(s) || isBinaryOpFillModifier(s)
 }
 
 func isPrefixModifier(s string) bool {

parser_test.go

@@ -342,6 +342,22 @@ func TestParseSuccess(t *testing.T) {
 	another(`a + oN() gROUp_rigHt(*) PREfix "bar" b`, `a + on() group_right(*) prefix "bar" b`)
 	same(`a + on(a) group_left(x,y) prefix "foo" b`)
 	same(`a + on(a,b) group_right(z) prefix "bar" b`)
+
+	// fill modifiers
+	same(`m * on(job) fill_right(0) n`)
+	same(`m * on(job) fill_left(0) n`)
+	same(`m * on(job) fill_left(0) fill_right(1) n`)
+	same(`m * on(job) fill(0) n`)
+	another(`m * on(job) FILL_RIGHT(0) n`, `m * on(job) fill_right(0) n`)
+	another(`m * on(job) FILL(0) n`, `m * on(job) fill(0) n`)
+	same(`m * on(job) fill_right(-1) n`)
+	same(`m * on(job) fill_left(inf) n`)
+	same(`m * on(job) fill(NaN) n`)
+	same(`m * on(job) group_left() fill_right(0) n`)
+	same(`m * fill_right(0) n`)
+	another(`a + fill_right`, `a + (fill_right)`)
+	another(`a + fill_left`, `a + (fill_left)`)
+	another(`a + fill`, `a + (fill)`)
 	another(`5 - 1 + 3 * 2 ^ 2 ^ 3 - 2  OR Metric {Bar= "Baz", aaa!="bb",cc=~"dd" ,zz !~"ff" } `,
 		`770 or Metric{Bar="Baz",aaa!="bb",cc=~"dd",zz!~"ff"}`)