Add `atan2` binary operator

Signed-off-by: Levi Harrison <git@leviharrison.dev>

promql/engine.go

@@ -2116,6 +2116,8 @@ func vectorElemBinop(op parser.ItemType, lhs, rhs float64) (float64, bool) {
 		return lhs, lhs >= rhs
 	case parser.LTE:
 		return lhs, lhs <= rhs
+	case parser.ATAN2:
+		return math.Atan2(lhs, rhs), true
 	}
 	panic(errors.Errorf("operator %q not allowed for operations between Vectors", op))
 }

promql/parser/generated_parser.y

@@ -84,6 +84,7 @@ NEQ_REGEX
 POW
 SUB
 AT
+ATAN2
 %token	operatorsEnd
 
 // Aggregators.
@@ -156,7 +157,7 @@ START_METRIC_SELECTOR
 %left LAND LUNLESS
 %left EQLC GTE GTR LSS LTE NEQ
 %left ADD SUB
-%left MUL DIV MOD
+%left MUL DIV MOD ATAN2
 %right POW
 
 // Offset modifiers do not have associativity.
@@ -237,6 +238,7 @@ aggregate_modifier:
 
 // Operator precedence only works if each of those is listed separately.
 binary_expr     : expr ADD     bin_modifier expr { $$ = yylex.(*parser).newBinaryExpression($1, $2, $3, $4) }
+                | expr ATAN2   bin_modifier expr { $$ = yylex.(*parser).newBinaryExpression($1, $2, $3, $4) }
                 | expr DIV     bin_modifier expr { $$ = yylex.(*parser).newBinaryExpression($1, $2, $3, $4) }
                 | expr EQLC    bin_modifier expr { $$ = yylex.(*parser).newBinaryExpression($1, $2, $3, $4) }
                 | expr GTE     bin_modifier expr { $$ = yylex.(*parser).newBinaryExpression($1, $2, $3, $4) }

promql/parser/lex.go

@@ -97,6 +97,7 @@ var key = map[string]ItemType{
 	"and":    LAND,
 	"or":     LOR,
 	"unless": LUNLESS,
+	"atan2":  ATAN2,
 
 	// Aggregators.
 	"sum":          SUM,