Add interpliationFuncKeys to find keys in a map

interpolation/maps.go

@@ -2,6 +2,7 @@ package interpolation
 
 import (
 	"fmt"
+	"sort"
 
 	"github.com/hashicorp/hil"
 
@@ -58,3 +59,31 @@ func interpolationFuncMap() ast.Function {
 		},
 	}
 }
+
+// interpolationFuncKeys returns the keys of the provided map sorted in dictionary order
+func interpolationFuncKeys() ast.Function {
+	return ast.Function{
+		ArgTypes:   []ast.Type{ast.TypeMap},
+		ReturnType: ast.TypeList,
+		Variadic:   false,
+		Callback: func(inputs []interface{}) (interface{}, error) {
+			mapInput := inputs[0].(map[string]ast.Variable)
+			keys := make([]string, 0, len(mapInput)+1)
+			result := make([]ast.Variable, 0, len(mapInput)+1)
+			for key := range mapInput {
+				keys = append(keys, key)
+			}
+			sort.Strings(keys)
+
+			for _, key := range keys {
+				nativeKey, err := hil.InterfaceToVariable(key)
+				if err != nil {
+					return nil, err
+				}
+				result = append(result, nativeKey)
+			}
+
+			return result, nil
+		},
+	}
+}

interpolation/maps_test.go

@@ -80,3 +80,36 @@ func TestInterpolationFuncMap(t *testing.T) {
 		})
 	}
 }
+
+func TestInterpolationFuncKeys(t *testing.T) {
+	testCases := []functionTestCase{
+		{
+			description: "Returns the keys",
+			text:        `${keys(foo)}`,
+			expectation: []interface{}{"bar", "bar2"},
+			vars: map[string]ast.Variable{
+				"foo": ast.Variable{
+					Type: ast.TypeMap,
+					Value: map[string]ast.Variable{
+						"bar2": ast.Variable{
+							Type:  ast.TypeString,
+							Value: "other2",
+						},
+						"bar": ast.Variable{
+							Type:  ast.TypeString,
+							Value: "other",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	keysTestFunc := testInterpolationFunc("keys", interpolationFuncKeys)
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			keysTestFunc(t, tc)
+		})
+	}
+}