Merge pull request #97 from jamslinger/division-by-zero

Don't panic in filter divided_by on division by zero

filters/standard_filters.go

@@ -3,6 +3,7 @@ package filters
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"html"
 	"math"
@@ -17,6 +18,8 @@ import (
 	"github.com/osteele/tuesday"
 )
 
+var errDivisionByZero = errors.New("division by zero")
+
 // A FilterDictionary holds filters.
 type FilterDictionary interface {
 	AddFilter(string, any)
@@ -100,14 +103,42 @@ func AddStandardFilters(fd FilterDictionary) { //nolint: gocyclo
 	fd.AddFilter("times", func(a, b float64) float64 {
 		return a * b
 	})
-	fd.AddFilter("divided_by", func(a float64, b any) any {
+	fd.AddFilter("divided_by", func(a float64, b any) (any, error) {
+		divInt := func(a, b int64) (int64, error) {
+			if b == 0 {
+				return 0, errDivisionByZero
+			}
+			return a / b, nil
+		}
+		divFloat := func(a, b float64) (float64, error) {
+			if b == 0 {
+				return 0, errDivisionByZero
+			}
+			return a / b, nil
+		}
 		switch q := b.(type) {
-		case int, int16, int32, int64:
-			return int(a) / q.(int)
-		case float32, float64:
-			return a / b.(float64)
+		case int:
+			return divInt(int64(a), int64(q))
+		case int8:
+			return divInt(int64(a), int64(q))
+		case int16:
+			return divInt(int64(a), int64(q))
+		case int32:
+			return divInt(int64(a), int64(q))
+		case int64:
+			return divInt(int64(a), q)
+		case uint8:
+			return divInt(int64(a), int64(q))
+		case uint16:
+			return divInt(int64(a), int64(q))
+		case uint32:
+			return divInt(int64(a), int64(q))
+		case float32:
+			return divFloat(a, float64(q))
+		case float64:
+			return divFloat(a, q)
 		default:
-			return nil
+			return nil, fmt.Errorf("invalid divisor: '%v'", b)
 		}
 	})
 	fd.AddFilter("round", func(n float64, places func(int) int) float64 {

filters/standard_filters_test.go

@@ -184,7 +184,6 @@ Liquid" | slice: 2, 4`, "quid"},
 	{`5 | divided_by: 3`, 1},
 	{`20 | divided_by: 7`, 2},
 	{`20 | divided_by: 7.0`, 2.857142857142857},
-	{`20 | divided_by: 's'`, nil},
 
 	{`1.2 | round`, 1.0},
 	{`2.7 | round`, 3.0},
@@ -197,6 +196,14 @@ Liquid" | slice: 2, 4`, "quid"},
 	{`"1" | type`, `string`},
 }
 
+var filterErrorTests = []struct {
+	in    string
+	error string
+}{
+	{`20 | divided_by: 's'`, `error applying filter "divided_by" ("invalid divisor: 's'")`},
+	{`20 | divided_by: 0`, `error applying filter "divided_by" ("division by zero")`},
+}
+
 var filterTestBindings = map[string]any{
 	"empty_array":     []any{},
 	"empty_map":       map[string]any{},
@@ -272,7 +279,14 @@ func TestFilters(t *testing.T) {
 		t.Run(fmt.Sprintf("%02d", i+1), func(t *testing.T) {
 			actual, err := expressions.EvaluateString(test.in, context)
 			require.NoErrorf(t, err, test.in)
-			require.Equalf(t, test.expected, actual, test.in)
+			require.EqualValuesf(t, test.expected, actual, test.in)
+		})
+	}
+
+	for i, test := range filterErrorTests {
+		t.Run(fmt.Sprintf("%02d", i+len(filterTests)+1), func(t *testing.T) {
+			_, err := expressions.EvaluateString(test.in, context)
+			require.EqualErrorf(t, err, test.error, test.in)
 		})
 	}
 }