porting matchkeys

lang/funcs/collection.go

@@ -232,7 +232,7 @@ var IndexFunc = function.New(&function.Spec{
 		}
 
 		if args[0].LengthInt() == 0 { // Easy path
-			return cty.NilVal, fmt.Errorf("Cannot search an empty list")
+			return cty.NilVal, fmt.Errorf("cannot search an empty list")
 		}
 
 		for it := args[0].ElementIterator(); it.Next(); {
@@ -302,7 +302,7 @@ var ChunklistFunc = function.New(&function.Spec{
 		}
 
 		if size < 0 {
-			return cty.NilVal, fmt.Errorf("The size argument must be positive")
+			return cty.NilVal, fmt.Errorf("the size argument must be positive")
 		}
 
 		output := make([]cty.Value, 0)
@@ -334,6 +334,72 @@ var ChunklistFunc = function.New(&function.Spec{
 	},
 })
 
+// MatchkeysFunc contructs a function that constructs a new list by taking a
+// subset of elements from one list whose indexes match the corresponding
+// indexes of values in another list.
+var MatchkeysFunc = function.New(&function.Spec{
+	Params: []function.Parameter{
+		{
+			Name: "values",
+			Type: cty.List(cty.DynamicPseudoType),
+		},
+		{
+			Name: "keys",
+			Type: cty.List(cty.DynamicPseudoType),
+		},
+		{
+			Name: "searchset",
+			Type: cty.List(cty.DynamicPseudoType),
+		},
+	},
+	Type: func(args []cty.Value) (cty.Type, error) {
+		if args[1].Type() != args[2].Type() {
+			return cty.NilType, fmt.Errorf("lists must be of the same type")
+		}
+
+		if args[0].LengthInt() != args[1].LengthInt() {
+			return cty.NilType, fmt.Errorf("length of keys and values should be equal")
+		}
+		return args[0].Type(), nil
+	},
+	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		output := make([]cty.Value, 0)
+
+		values := args[0]
+		keys := args[1]
+		searchset := args[2]
+
+		// if searchset is empty, return an empty list.
+		if searchset.LengthInt() == 0 {
+			return cty.ListValEmpty(*retType.ListElementType()), nil
+		}
+
+		i := 0
+		for it := keys.ElementIterator(); it.Next(); {
+			_, key := it.Element()
+			for iter := searchset.ElementIterator(); iter.Next(); {
+				_, search := iter.Element()
+				eq, err := stdlib.Equal(key, search)
+				if err != nil {
+					return cty.NilVal, err
+				}
+				if eq.True() {
+					v := values.Index(cty.NumberIntVal(int64(i)))
+					output = append(output, v)
+					break
+				}
+			}
+			i++
+		}
+
+		// if we haven't matched any key, then output is an empty list.
+		if len(output) == 0 {
+			return cty.ListValEmpty(*retType.ListElementType()), nil
+		}
+		return cty.ListVal(output), nil
+	},
+})
+
 // helper function to add an element to a list, if it does not already exsit
 func appendIfMissing(slice []cty.Value, element cty.Value) ([]cty.Value, error) {
 	for _, ele := range slice {
@@ -392,3 +458,9 @@ func Distinct(list cty.Value) (cty.Value, error) {
 func Chunklist(list, size cty.Value) (cty.Value, error) {
 	return ChunklistFunc.Call([]cty.Value{list, size})
 }
+
+// Matchkeys constructs a new list by taking a subset of elements from one list
+// whose indexes match the corresponding indexes of values in another list.
+func Matchkeys(values, keys, searchset cty.Value) (cty.Value, error) {
+	return MatchkeysFunc.Call([]cty.Value{values, keys, searchset})
+}

lang/funcs/collection_test.go

@@ -786,3 +786,179 @@ func TestChunklist(t *testing.T) {
 		})
 	}
 }
+
+func TestMatchkeys(t *testing.T) {
+	tests := []struct {
+		Keys      cty.Value
+		Values    cty.Value
+		Searchset cty.Value
+		Want      cty.Value
+		Err       bool
+	}{
+		{ // normal usage
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref1"),
+				cty.StringVal("ref2"),
+				cty.StringVal("ref3"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref1"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			false,
+		},
+		{ // normal usage 2, check the order
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref1"),
+				cty.StringVal("ref2"),
+				cty.StringVal("ref3"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref2"),
+				cty.StringVal("ref1"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+			}),
+			false,
+		},
+		{ // no matches
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref1"),
+				cty.StringVal("ref2"),
+				cty.StringVal("ref3"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref4"),
+			}),
+			cty.ListValEmpty(cty.String),
+			false,
+		},
+		{ // no matches 2
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("ref1"),
+				cty.StringVal("ref2"),
+				cty.StringVal("ref3"),
+			}),
+			cty.ListValEmpty(cty.String),
+			cty.ListValEmpty(cty.String),
+			false,
+		},
+		{ // zero case
+			cty.ListValEmpty(cty.String),
+			cty.ListValEmpty(cty.String),
+			cty.ListVal([]cty.Value{cty.StringVal("nope")}),
+			cty.ListValEmpty(cty.String),
+			false,
+		},
+		{ // complex values
+			cty.ListVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("a"),
+				}),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("a"),
+				}),
+			}),
+			false,
+		},
+		// errors
+		{ // different types
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.NumberIntVal(1),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.NilVal,
+			true,
+		},
+		{ // different types
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+				}),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.NilVal,
+			true,
+		},
+		{ // lists of different length
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+			}),
+			cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+			}),
+			cty.NilVal,
+			true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("matchkeys(%#v, %#v, %#v)", test.Keys, test.Values, test.Searchset), func(t *testing.T) {
+			got, err := Matchkeys(test.Keys, test.Values, test.Searchset)
+
+			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)
+			}
+		})
+	}
+}

lang/functions.go

@@ -54,7 +54,7 @@ func (s *Scope) Functions() map[string]function.Function {
 			"chunklist":    funcs.ChunklistFunc,
 			"file":         funcs.MakeFileFunc(s.BaseDir, false),
 			"filebase64":   funcs.MakeFileFunc(s.BaseDir, true),
-			"matchkeys":    unimplFunc, // TODO
+			"matchkeys":    funcs.MatchkeysFunc,
 			"flatten":      unimplFunc, // TODO
 			"floor":        funcs.FloorFunc,
 			"format":       stdlib.FormatFunc,