add negative offset ability

Signed-off-by: schou <pschou@users.noreply.github.com>

promql/parser/generated_parser.y

@@ -383,7 +383,12 @@ paren_expr      : LEFT_PAREN expr RIGHT_PAREN
 
 offset_expr: expr OFFSET duration
                         {
-                        yylex.(*parser).addOffset($1, $3)
+                        yylex.(*parser).addOffset($1, $3, 1)
+                        $$ = $1
+                        }
+                | expr OFFSET SUB duration
+                        {
+                        yylex.(*parser).addOffset($1, $4, -1)
                         $$ = $1
                         }
                 | expr OFFSET error

promql/parser/parse.go

@@ -683,7 +683,7 @@ func (p *parser) newLabelMatcher(label Item, operator Item, value Item) *labels.
 }
 
 // addOffset is used to set the offset in the generated parser.
-func (p *parser) addOffset(e Node, offset time.Duration) {
+func (p *parser) addOffset(e Node, offset time.Duration, direction int) {
 	var orgoffsetp *time.Duration
 	var endPosp *Pos
 
@@ -711,7 +711,7 @@ func (p *parser) addOffset(e Node, offset time.Duration) {
 	if *orgoffsetp != 0 {
 		p.addParseErrf(e.PositionRange(), "offset may not be set multiple times")
 	} else if orgoffsetp != nil {
-		*orgoffsetp = offset
+		*orgoffsetp = offset * time.Duration(direction)
 	}
 
 	*endPosp = p.lastClosing

promql/parser/parse_test.go

@@ -1362,6 +1362,19 @@ var testExpr = []struct {
 				End:   13,
 			},
 		},
+	}, {
+		input: "foo offset -7m",
+		expected: &VectorSelector{
+			Name:           "foo",
+			OriginalOffset: -7 * time.Minute,
+			LabelMatchers: []*labels.Matcher{
+				MustLabelMatcher(labels.MatchEqual, model.MetricNameLabel, "foo"),
+			},
+			PosRange: PositionRange{
+				Start: 0,
+				End:   14,
+			},
+		},
 	}, {
 		input: `foo OFFSET 1h30m`,
 		expected: &VectorSelector{