Add fromJson function

defaults.go

@@ -3,6 +3,7 @@ package sprig
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"reflect"
 	"strings"
 )
@@ -63,6 +64,24 @@ func coalesce(v ...interface{}) interface{} {
 	return nil
 }
 
+// fromJSON decodes a JSON string to an item.
+func fromJson(v interface{}) interface{} {
+	var result interface{}
+	switch v := v.(type) {
+	case []byte:
+		if err := json.Unmarshal(v, &result); err != nil {
+			panic(err)
+		}
+	case string:
+		if err := json.Unmarshal([]byte(v), &result); err != nil {
+			panic(err)
+		}
+	default:
+		panic(fmt.Errorf("Cannot decode JSON from type %T", v))
+	}
+	return result
+}
+
 // toJson encodes an item into a JSON string
 func toJson(v interface{}) string {
 	output, _ := json.Marshal(v)

defaults_test.go

@@ -83,6 +83,16 @@ func TestCoalesce(t *testing.T) {
 	}
 }
 
+func TestFromJson(t *testing.T) {
+	dict := map[string]interface{}{"Top": `{"number":42}`}
+
+	tpl := `{{ index (.Top | fromJson) "number" }}`
+	expected := `42`
+	if err := runtv(tpl, expected, dict); err != nil {
+		t.Error(err)
+	}
+}
+
 func TestToJson(t *testing.T) {
 	dict := map[string]interface{}{"Top": map[string]interface{}{"bool": true, "string": "test", "number": 42}}
 

docs/defaults.md

@@ -58,6 +58,16 @@ The above will first check to see if `.name` is empty. If it is not, it will ret
 that value. If it _is_ empty, `coalesce` will evaluate `.parent.name` for emptiness.
 Finally, if both `.name` and `.parent.name` are empty, it will return `Matt`.
 
+## fromJson
+
+The `fromJson` function decodes data from a JSON string. If the item cannot be decoded the function will return an error.
+
+```
+fromJson .Value
+```
+
+The above decodes the JSON data from `.Value`.
+
 ## toJson, mustToJson
 
 The `toJson` function encodes an item into a JSON string. If the item cannot be converted to JSON the function will return an empty string.

functions.go

@@ -217,6 +217,7 @@ var genericMap = map[string]interface{}{
 	"empty":            empty,
 	"coalesce":         coalesce,
 	"compact":          compact,
+	"fromJson":         fromJson,
 	"mustCompact":      mustCompact,
 	"toJson":           toJson,
 	"toPrettyJson":     toPrettyJson,