function/stdlib: SliceFunc mark handling

SliceFunc will now preserve marks on the input list as a whole, and any individual elements.

cty/function/stdlib/collection.go

@@ -1023,8 +1023,9 @@ var SetProductFunc = function.New(&function.Spec{
 var SliceFunc = function.New(&function.Spec{
 	Params: []function.Parameter{
 		{
-			Name: "list",
-			Type: cty.DynamicPseudoType,
+			Name:        "list",
+			Type:        cty.DynamicPseudoType,
+			AllowMarked: true,
 		},
 		{
 			Name: "start_index",
@@ -1063,10 +1064,10 @@ var SliceFunc = function.New(&function.Spec{
 		return cty.Tuple(argTy.TupleElementTypes()[startIndex:endIndex]), nil
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
-		inputList := args[0]
+		inputList, marks := args[0].Unmark()
 
 		if retType == cty.DynamicPseudoType {
-			return cty.DynamicVal, nil
+			return cty.DynamicVal.WithMarks(marks), nil
 		}
 
 		// we ignore idxsKnown return value here because the indices are always
@@ -1078,28 +1079,31 @@ var SliceFunc = function.New(&function.Spec{
 
 		if endIndex-startIndex == 0 {
 			if retType.IsTupleType() {
-				return cty.EmptyTupleVal, nil
+				return cty.EmptyTupleVal.WithMarks(marks), nil
 			}
-			return cty.ListValEmpty(retType.ElementType()), nil
+			return cty.ListValEmpty(retType.ElementType()).WithMarks(marks), nil
 		}
 
 		outputList := inputList.AsValueSlice()[startIndex:endIndex]
 
 		if retType.IsTupleType() {
-			return cty.TupleVal(outputList), nil
+			return cty.TupleVal(outputList).WithMarks(marks), nil
 		}
 
-		return cty.ListVal(outputList), nil
+		return cty.ListVal(outputList).WithMarks(marks), nil
 	},
 })
 
 func sliceIndexes(args []cty.Value) (int, int, bool, error) {
 	var startIndex, endIndex, length int
 	var startKnown, endKnown, lengthKnown bool
 
+	// remove marks from args[0]
+	list, _ := args[0].Unmark()
+
 	// If it's a tuple then we always know the length by the type, but collections might be unknown or have unknown length
-	if args[0].Type().IsTupleType() || args[0].Length().IsKnown() {
-		length = args[0].LengthInt()
+	if list.Type().IsTupleType() || list.Length().IsKnown() {
+		length = list.LengthInt()
 		lengthKnown = true
 	}
 

cty/function/stdlib/collection_test.go

@@ -2347,3 +2347,77 @@ func TestReverseList(t *testing.T) {
 		})
 	}
 }
+
+func TestSlice(t *testing.T) {
+	tests := []struct {
+		Input cty.Value
+		Start cty.Value
+		End   cty.Value
+		Want  cty.Value
+		Err   string
+	}{
+		{
+			Input: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}),
+			Start: cty.NumberIntVal(0),
+			End:   cty.NumberIntVal(2),
+			Want: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+			}),
+			Err: ``,
+		},
+		{ // The entire input list is marked, so the return should be marked
+			Input: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}).Mark("bloop"),
+			Start: cty.NumberIntVal(0),
+			End:   cty.NumberIntVal(2),
+			Want: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+			}).Mark("bloop"),
+			Err: ``,
+		},
+		{ // individual element marks should be preserved
+			Input: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b").Mark("bloop"),
+				cty.StringVal("c"),
+			}),
+			Start: cty.NumberIntVal(0),
+			End:   cty.NumberIntVal(2),
+			Want: cty.ListVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b").Mark("bloop"),
+			}),
+			Err: ``,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("Slice(%#v)", test.Input), func(t *testing.T) {
+			got, err := Slice(test.Input, test.Start, test.End)
+			if test.Err != "" {
+				if err == nil {
+					t.Fatal("succeeded; want error")
+				}
+				if got, want := err.Error(), test.Err; got != want {
+					t.Fatalf("wrong error\ngot:  %s\nwant: %s", got, want)
+				}
+				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)
+			}
+		})
+	}
+}