functions: KeysFunc

lang/funcs/collection.go

@@ -371,6 +371,30 @@ func flattener(finalList []cty.Value, flattenList cty.Value) []cty.Value {
 	return finalList
 }
 
+// KeysFunc contructs a function that takes a map and returns a sorted list of the map keys.
+var KeysFunc = function.New(&function.Spec{
+	Params: []function.Parameter{
+		{
+			Name: "inputMap",
+			Type: cty.Map(cty.DynamicPseudoType),
+		},
+	},
+	Type: function.StaticReturnType(cty.List(cty.String)),
+	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		var keys []cty.Value
+
+		for it := args[0].ElementIterator(); it.Next(); {
+			k, _ := it.Element()
+			fmt.Printf("appending %#v to %#v\n", k, keys)
+			keys = append(keys, k)
+			if err != nil {
+				return cty.ListValEmpty(cty.String), err
+			}
+		}
+		return cty.ListVal(keys), nil
+	},
+})
+
 // ListFunc contructs a function that takes an arbitrary number of arguments
 // and returns a list containing those values in the same order.
 //
@@ -553,7 +577,7 @@ var MatchkeysFunc = function.New(&function.Spec{
 	},
 })
 
-// helper function to add an element to a list, if it does not already exsit
+// helper function to add an element to a list, if it does not already exist
 func appendIfMissing(slice []cty.Value, element cty.Value) ([]cty.Value, error) {
 	for _, ele := range slice {
 		eq, err := stdlib.Equal(ele, element)
@@ -618,6 +642,11 @@ func Flatten(list cty.Value) (cty.Value, error) {
 	return FlattenFunc.Call([]cty.Value{list})
 }
 
+// Keys takes a map and returns a sorted list of the map keys.
+func Keys(inputMap cty.Value) (cty.Value, error) {
+	return KeysFunc.Call([]cty.Value{inputMap})
+}
+
 // List takes any number of list arguments and returns a list containing those
 //  values in the same order.
 func List(args ...cty.Value) (cty.Value, error) {

lang/funcs/collection_test.go

@@ -839,6 +839,50 @@ func TestFlatten(t *testing.T) {
 	}
 }
 
+func TestKeys(t *testing.T) {
+	tests := []struct {
+		Map  cty.Value
+		Want cty.Value
+		Err  bool
+	}{
+		{
+			cty.MapVal(map[string]cty.Value{
+				"hello":   cty.NumberIntVal(1),
+				"goodbye": cty.NumberIntVal(42),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("goodbye"),
+				cty.StringVal("hello"),
+			}),
+			false,
+		},
+		{ // Not a map
+			cty.StringVal("foo"),
+			cty.NilVal,
+			true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("keys(%#v)", test.Map), func(t *testing.T) {
+			got, err := Keys(test.Map)
+
+			if test.Err {
+				if err == nil {
+					t.Fatal("succeeded; want error")
+				}
+				return
+			} else if err != nil {
+				t.Fatalf("unexpected error: %s", err)
+			}
+
+			if !got.RawEquals(test.Want) {
+				t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, test.Want)
+			}
+		})
+	}
+}
+
 func TestList(t *testing.T) {
 	tests := []struct {
 		Values []cty.Value

lang/functions.go

@@ -63,7 +63,7 @@ func (s *Scope) Functions() map[string]function.Function {
 			"join":         funcs.JoinFunc,
 			"jsondecode":   stdlib.JSONDecodeFunc,
 			"jsonencode":   stdlib.JSONEncodeFunc,
-			"keys":         unimplFunc, // TODO
+			"keys":         funcs.KeysFunc,
 			"length":       funcs.LengthFunc,
 			"list":         funcs.ListFunc,
 			"log":          funcs.LogFunc,