Merge pull request #21174 from hashicorp/jbardin/func-types

lang/funcs: better type handling in interpolation funcs

lang/funcs/collection.go

@@ -1,6 +1,7 @@
 package funcs
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 
@@ -43,7 +44,7 @@ var ElementFunc = function.New(&function.Spec{
 				return cty.DynamicPseudoType, fmt.Errorf("invalid index: %s", err)
 			}
 			if len(etys) == 0 {
-				return cty.DynamicPseudoType, fmt.Errorf("cannot use element function with an empty list")
+				return cty.DynamicPseudoType, errors.New("cannot use element function with an empty list")
 			}
 			index = index % len(etys)
 			return etys[index], nil
@@ -65,7 +66,7 @@ var ElementFunc = function.New(&function.Spec{
 
 		l := args[0].LengthInt()
 		if l == 0 {
-			return cty.DynamicVal, fmt.Errorf("cannot use element function with an empty list")
+			return cty.DynamicVal, errors.New("cannot use element function with an empty list")
 		}
 		index = index % l
 
@@ -90,7 +91,7 @@ var LengthFunc = function.New(&function.Spec{
 		case collTy == cty.String || collTy.IsTupleType() || collTy.IsObjectType() || collTy.IsListType() || collTy.IsMapType() || collTy.IsSetType() || collTy == cty.DynamicPseudoType:
 			return cty.Number, nil
 		default:
-			return cty.Number, fmt.Errorf("argument must be a string, a collection type, or a structural type")
+			return cty.Number, errors.New("argument must be a string, a collection type, or a structural type")
 		}
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
@@ -114,7 +115,7 @@ var LengthFunc = function.New(&function.Spec{
 			return coll.Length(), nil
 		default:
 			// Should never happen, because of the checks in our Type func above
-			return cty.UnknownVal(cty.Number), fmt.Errorf("impossible value type for length(...)")
+			return cty.UnknownVal(cty.Number), errors.New("impossible value type for length(...)")
 		}
 	},
 })
@@ -139,7 +140,7 @@ var CoalesceFunc = function.New(&function.Spec{
 		}
 		retType, _ := convert.UnifyUnsafe(argTypes)
 		if retType == cty.NilType {
-			return cty.NilType, fmt.Errorf("all arguments must have the same type")
+			return cty.NilType, errors.New("all arguments must have the same type")
 		}
 		return retType, nil
 	},
@@ -159,7 +160,7 @@ var CoalesceFunc = function.New(&function.Spec{
 
 			return argVal, nil
 		}
-		return cty.NilVal, fmt.Errorf("no non-null, non-empty-string arguments")
+		return cty.NilVal, errors.New("no non-null, non-empty-string arguments")
 	},
 })
 
@@ -169,32 +170,43 @@ var CoalesceListFunc = function.New(&function.Spec{
 	Params: []function.Parameter{},
 	VarParam: &function.Parameter{
 		Name:             "vals",
-		Type:             cty.List(cty.DynamicPseudoType),
+		Type:             cty.DynamicPseudoType,
 		AllowUnknown:     true,
 		AllowDynamicType: true,
 		AllowNull:        true,
 	},
 	Type: func(args []cty.Value) (ret cty.Type, err error) {
 		if len(args) == 0 {
-			return cty.NilType, fmt.Errorf("at least one argument is required")
+			return cty.NilType, errors.New("at least one argument is required")
 		}
 
 		argTypes := make([]cty.Type, len(args))
 
 		for i, arg := range args {
+			// if any argument is unknown, we can't be certain know which type we will return
+			if !arg.IsKnown() {
+				return cty.DynamicPseudoType, nil
+			}
+			ty := arg.Type()
+
+			if !ty.IsListType() && !ty.IsTupleType() {
+				return cty.NilType, errors.New("coalescelist arguments must be lists or tuples")
+			}
+
 			argTypes[i] = arg.Type()
 		}
 
-		retType, _ := convert.UnifyUnsafe(argTypes)
+		last := argTypes[0]
-		if retType == cty.NilType {
+		// If there are mixed types, we have to return a dynamic type.
-			return cty.NilType, fmt.Errorf("all arguments must have the same type")
+		for _, next := range argTypes[1:] {
+			if !next.Equals(last) {
+				return cty.DynamicPseudoType, nil
+			}
 		}
 
-		return retType, nil
+		return last, nil
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
-
-		vals := make([]cty.Value, 0, len(args))
 		for _, arg := range args {
 			if !arg.IsKnown() {
 				// If we run into an unknown list at some point, we can't
@@ -203,21 +215,12 @@ var CoalesceListFunc = function.New(&function.Spec{
 				return cty.UnknownVal(retType), nil
 			}
 
-			// We already know this will succeed because of the checks in our Type func above
+			if arg.LengthInt() > 0 {
-			arg, _ = convert.Convert(arg, retType)
+				return arg, nil
-
-			it := arg.ElementIterator()
-			for it.Next() {
-				_, v := it.Element()
-				vals = append(vals, v)
-			}
-
-			if len(vals) > 0 {
-				return cty.ListVal(vals), nil
 			}
 		}
 
-		return cty.NilVal, fmt.Errorf("no non-null arguments")
+		return cty.NilVal, errors.New("no non-null arguments")
 	},
 })
 
@@ -265,7 +268,7 @@ var ContainsFunc = function.New(&function.Spec{
 	Params: []function.Parameter{
 		{
 			Name: "list",
-			Type: cty.List(cty.DynamicPseudoType),
+			Type: cty.DynamicPseudoType,
 		},
 		{
 			Name: "value",
@@ -274,8 +277,14 @@ var ContainsFunc = function.New(&function.Spec{
 	},
 	Type: function.StaticReturnType(cty.Bool),
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		arg := args[0]
+		ty := arg.Type()
 
-		_, err = Index(args[0], args[1])
+		if !ty.IsListType() && !ty.IsTupleType() && !ty.IsSetType() {
+			return cty.NilVal, errors.New("argument must be list, tuple, or set")
+		}
+
+		_, err = Index(cty.TupleVal(arg.AsValueSlice()), args[1])
 		if err != nil {
 			return cty.False, nil
 		}
@@ -299,7 +308,7 @@ var IndexFunc = function.New(&function.Spec{
 	Type: function.StaticReturnType(cty.Number),
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		if !(args[0].Type().IsListType() || args[0].Type().IsTupleType()) {
-			return cty.NilVal, fmt.Errorf("argument must be a list or tuple")
+			return cty.NilVal, errors.New("argument must be a list or tuple")
 		}
 
 		if !args[0].IsKnown() {
@@ -307,7 +316,7 @@ 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, errors.New("cannot search an empty list")
 		}
 
 		for it := args[0].ElementIterator(); it.Next(); {
@@ -323,7 +332,7 @@ var IndexFunc = function.New(&function.Spec{
 				return i, nil
 			}
 		}
-		return cty.NilVal, fmt.Errorf("item not found")
+		return cty.NilVal, errors.New("item not found")
 
 	},
 })
@@ -378,7 +387,7 @@ var ChunklistFunc = function.New(&function.Spec{
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		listVal := args[0]
-		if !listVal.IsWhollyKnown() {
+		if !listVal.IsKnown() {
 			return cty.UnknownVal(retType), nil
 		}
 
@@ -389,7 +398,7 @@ var ChunklistFunc = function.New(&function.Spec{
 		}
 
 		if size < 0 {
-			return cty.NilVal, fmt.Errorf("the size argument must be positive")
+			return cty.NilVal, errors.New("the size argument must be positive")
 		}
 
 		output := make([]cty.Value, 0)
@@ -437,11 +446,14 @@ var FlattenFunc = function.New(&function.Spec{
 
 		argTy := args[0].Type()
 		if !argTy.IsListType() && !argTy.IsSetType() && !argTy.IsTupleType() {
-			return cty.NilType, fmt.Errorf("can only flatten lists, sets and tuples")
+			return cty.NilType, errors.New("can only flatten lists, sets and tuples")
+		}
+
+		retVal, known := flattener(args[0])
+		if !known {
+			return cty.DynamicPseudoType, nil
 		}
 
-		outputList := make([]cty.Value, 0)
-		retVal := flattener(outputList, args[0])
 		tys := make([]cty.Type, len(retVal))
 		for i, ty := range retVal {
 			tys[i] = ty.Type()
@@ -450,30 +462,41 @@ var FlattenFunc = function.New(&function.Spec{
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		inputList := args[0]
-		if !inputList.IsWhollyKnown() {
-			return cty.UnknownVal(retType), nil
-		}
 		if inputList.LengthInt() == 0 {
 			return cty.EmptyTupleVal, nil
 		}
-		outputList := make([]cty.Value, 0)
 
-		return cty.TupleVal(flattener(outputList, inputList)), nil
+		out, known := flattener(inputList)
+		if !known {
+			return cty.UnknownVal(retType), nil
+		}
+
+		return cty.TupleVal(out), nil
 	},
 })
 
-// Flatten until it's not a cty.List
+// Flatten until it's not a cty.List, and return whether the value is known.
-func flattener(finalList []cty.Value, flattenList cty.Value) []cty.Value {
+// We can flatten lists with unknown values, as long as they are not
+// lists themselves.
+func flattener(flattenList cty.Value) ([]cty.Value, bool) {
+	out := make([]cty.Value, 0)
 	for it := flattenList.ElementIterator(); it.Next(); {
 		_, val := it.Element()
-
 		if val.Type().IsListType() || val.Type().IsSetType() || val.Type().IsTupleType() {
-			finalList = flattener(finalList, val)
+			if !val.IsKnown() {
+				return out, false
+			}
+
+			res, known := flattener(val)
+			if !known {
+				return res, known
+			}
+			out = append(out, res...)
 		} else {
-			finalList = append(finalList, val)
+			out = append(out, val)
 		}
 	}
-	return finalList
+	return out, true
 }
 
 // KeysFunc contructs a function that takes a map and returns a sorted list of the map keys.
@@ -561,7 +584,7 @@ var ListFunc = function.New(&function.Spec{
 	},
 	Type: func(args []cty.Value) (ret cty.Type, err error) {
 		if len(args) == 0 {
-			return cty.NilType, fmt.Errorf("at least one argument is required")
+			return cty.NilType, errors.New("at least one argument is required")
 		}
 
 		argTypes := make([]cty.Type, len(args))
@@ -572,7 +595,7 @@ var ListFunc = function.New(&function.Spec{
 
 		retType, _ := convert.UnifyUnsafe(argTypes)
 		if retType == cty.NilType {
-			return cty.NilType, fmt.Errorf("all arguments must have the same type")
+			return cty.NilType, errors.New("all arguments must have the same type")
 		}
 
 		return cty.List(retType), nil
@@ -666,7 +689,7 @@ var LookupFunc = function.New(&function.Spec{
 				case ty.Equals(cty.Number):
 					return cty.NumberVal(v.AsBigFloat()), nil
 				default:
-					return cty.NilVal, fmt.Errorf("lookup() can only be used with flat lists")
+					return cty.NilVal, errors.New("lookup() can only be used with flat lists")
 				}
 			}
 		}
@@ -712,7 +735,7 @@ var MapFunc = function.New(&function.Spec{
 
 		valType, _ := convert.UnifyUnsafe(argTypes)
 		if valType == cty.NilType {
-			return cty.NilType, fmt.Errorf("all arguments must have the same type")
+			return cty.NilType, errors.New("all arguments must have the same type")
 		}
 
 		return cty.Map(valType), nil
@@ -777,7 +800,7 @@ var MatchkeysFunc = function.New(&function.Spec{
 	},
 	Type: func(args []cty.Value) (cty.Type, error) {
 		if !args[1].Type().Equals(args[2].Type()) {
-			return cty.NilType, fmt.Errorf("lists must be of the same type")
+			return cty.NilType, errors.New("lists must be of the same type")
 		}
 
 		return args[0].Type(), nil
@@ -788,7 +811,7 @@ var MatchkeysFunc = function.New(&function.Spec{
 		}
 
 		if args[0].LengthInt() != args[1].LengthInt() {
-			return cty.ListValEmpty(retType.ElementType()), fmt.Errorf("length of keys and values should be equal")
+			return cty.ListValEmpty(retType.ElementType()), errors.New("length of keys and values should be equal")
 		}
 
 		output := make([]cty.Value, 0)
@@ -923,7 +946,7 @@ var SetProductFunc = function.New(&function.Spec{
 	},
 	Type: func(args []cty.Value) (retType cty.Type, err error) {
 		if len(args) < 2 {
-			return cty.NilType, fmt.Errorf("at least two arguments are required")
+			return cty.NilType, errors.New("at least two arguments are required")
 		}
 
 		listCount := 0
@@ -1040,7 +1063,7 @@ var SliceFunc = function.New(&function.Spec{
 	Params: []function.Parameter{
 		{
 			Name: "list",
-			Type: cty.List(cty.DynamicPseudoType),
+			Type: cty.DynamicPseudoType,
 		},
 		{
 			Name: "startIndex",
@@ -1052,50 +1075,71 @@ var SliceFunc = function.New(&function.Spec{
 		},
 	},
 	Type: func(args []cty.Value) (cty.Type, error) {
-		return args[0].Type(), nil
+		arg := args[0]
+		argTy := arg.Type()
+
+		if !argTy.IsListType() && !argTy.IsTupleType() {
+			return cty.NilType, errors.New("cannot slice a set, because its elements do not have indices; use the tolist function to force conversion to list if the ordering of the result is not important")
+		}
+
+		if argTy.IsListType() {
+			return argTy, nil
+		}
+
+		startIndex, endIndex, err := sliceIndexes(args, args[0].LengthInt())
+		if err != nil {
+			return cty.NilType, err
+		}
+
+		return cty.Tuple(argTy.TupleElementTypes()[startIndex:endIndex]), nil
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		inputList := args[0]
-		if !inputList.IsWhollyKnown() {
-			return cty.UnknownVal(retType), nil
-		}
-		var startIndex, endIndex int
 
-		if err = gocty.FromCtyValue(args[1], &startIndex); err != nil {
+		startIndex, endIndex, err := sliceIndexes(args, inputList.LengthInt())
-			return cty.NilVal, fmt.Errorf("invalid start index: %s", err)
+		if err != nil {
-		}
+			return cty.NilVal, err
-		if err = gocty.FromCtyValue(args[2], &endIndex); err != nil {
-			return cty.NilVal, fmt.Errorf("invalid start index: %s", err)
 		}
 
-		if startIndex < 0 {
+		if endIndex-startIndex == 0 {
-			return cty.NilVal, fmt.Errorf("from index must be >= 0")
+			if retType.IsTupleType() {
+				return cty.EmptyTupleVal, nil
 			}
-		if endIndex > inputList.LengthInt() {
-			return cty.NilVal, fmt.Errorf("to index must be <= length of the input list")
-		}
-		if startIndex > endIndex {
-			return cty.NilVal, fmt.Errorf("from index must be <= to index")
-		}
-
-		var outputList []cty.Value
-
-		i := 0
-		for it := inputList.ElementIterator(); it.Next(); {
-			_, v := it.Element()
-			if i >= startIndex && i < endIndex {
-				outputList = append(outputList, v)
-			}
-			i++
-		}
-
-		if len(outputList) == 0 {
 			return cty.ListValEmpty(retType.ElementType()), nil
 		}
+
+		outputList := inputList.AsValueSlice()[startIndex:endIndex]
+
+		if retType.IsTupleType() {
+			return cty.TupleVal(outputList), nil
+		}
+
 		return cty.ListVal(outputList), nil
 	},
 })
 
+func sliceIndexes(args []cty.Value, max int) (int, int, error) {
+	var startIndex, endIndex int
+
+	if err := gocty.FromCtyValue(args[1], &startIndex); err != nil {
+		return 0, 0, fmt.Errorf("invalid start index: %s", err)
+	}
+	if err := gocty.FromCtyValue(args[2], &endIndex); err != nil {
+		return 0, 0, fmt.Errorf("invalid start index: %s", err)
+	}
+
+	if startIndex < 0 {
+		return 0, 0, errors.New("from index must be greater than or equal to 0")
+	}
+	if endIndex > max {
+		return 0, 0, errors.New("to index must be less than or equal to the length of the input list")
+	}
+	if startIndex > endIndex {
+		return 0, 0, errors.New("from index must be less than or equal to index")
+	}
+	return startIndex, endIndex, nil
+}
+
 // TransposeFunc contructs a function that takes a map of lists of strings and
 // swaps the keys and values to produce a new map of lists of strings.
 var TransposeFunc = function.New(&function.Spec{
@@ -1120,7 +1164,7 @@ var TransposeFunc = function.New(&function.Spec{
 			for iter := inVal.ElementIterator(); iter.Next(); {
 				_, val := iter.Element()
 				if !val.Type().Equals(cty.String) {
-					return cty.MapValEmpty(cty.List(cty.String)), fmt.Errorf("input must be a map of lists of strings")
+					return cty.MapValEmpty(cty.List(cty.String)), errors.New("input must be a map of lists of strings")
 				}
 
 				outKey := val.AsString()
@@ -1180,7 +1224,7 @@ var ValuesFunc = function.New(&function.Spec{
 			}
 			return cty.Tuple(tys), nil
 		}
-		return cty.NilType, fmt.Errorf("values() requires a map as the first argument")
+		return cty.NilType, errors.New("values() requires a map as the first argument")
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		mapVar := args[0]
@@ -1247,7 +1291,7 @@ var ZipmapFunc = function.New(&function.Spec{
 			return cty.Object(atys), nil
 
 		default:
-			return cty.NilType, fmt.Errorf("values argument must be a list or tuple value")
+			return cty.NilType, errors.New("values argument must be a list or tuple value")
 		}
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {

lang/funcs/collection_test.go

@@ -417,7 +417,7 @@ func TestCoalesceList(t *testing.T) {
 				}),
 			},
 			cty.ListVal([]cty.Value{
-				cty.StringVal("1"), cty.StringVal("2"),
+				cty.NumberIntVal(1), cty.NumberIntVal(2),
 			}),
 			false,
 		},
@@ -476,7 +476,7 @@ func TestCoalesceList(t *testing.T) {
 				cty.ListValEmpty(cty.String),
 				cty.UnknownVal(cty.List(cty.String)),
 			},
-			cty.UnknownVal(cty.List(cty.String)),
+			cty.DynamicVal,
 			false,
 		},
 		{ // unknown list
@@ -486,13 +486,63 @@ func TestCoalesceList(t *testing.T) {
 					cty.StringVal("third"), cty.StringVal("fourth"),
 				}),
 			},
-			cty.UnknownVal(cty.List(cty.String)),
+			cty.DynamicVal,
 			false,
 		},
+		{ // unknown tuple
+			[]cty.Value{
+				cty.UnknownVal(cty.Tuple([]cty.Type{cty.String})),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.DynamicVal,
+			false,
+		},
+		{ // empty tuple
+			[]cty.Value{
+				cty.EmptyTupleVal,
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.ListVal([]cty.Value{
+				cty.StringVal("third"), cty.StringVal("fourth"),
+			}),
+			false,
+		},
+		{ // tuple value
+			[]cty.Value{
+				cty.TupleVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.NumberIntVal(2),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.NumberIntVal(2),
+			}),
+			false,
+		},
+		{ // reject set value
+			[]cty.Value{
+				cty.SetVal([]cty.Value{
+					cty.StringVal("a"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.NilVal,
+			true,
+		},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
-		t.Run(fmt.Sprintf("coalescelist(%#v)", test.Values), func(t *testing.T) {
+		t.Run(fmt.Sprintf("%d-coalescelist(%#v)", i, test.Values), func(t *testing.T) {
 			got, err := CoalesceList(test.Values...)
 
 			if test.Err {
@@ -671,6 +721,26 @@ func TestContains(t *testing.T) {
 			cty.BoolVal(true),
 			false,
 		},
+		{ // set val
+			cty.SetVal([]cty.Value{
+				cty.StringVal("quick"),
+				cty.StringVal("brown"),
+				cty.StringVal("fox"),
+			}),
+			cty.StringVal("quick"),
+			cty.BoolVal(true),
+			false,
+		},
+		{ // tuple val
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("quick"),
+				cty.StringVal("brown"),
+				cty.NumberIntVal(3),
+			}),
+			cty.NumberIntVal(3),
+			cty.BoolVal(true),
+			false,
+		},
 	}
 
 	for _, test := range tests {
@@ -993,13 +1063,29 @@ func TestChunklist(t *testing.T) {
 				cty.UnknownVal(cty.String),
 			}),
 			cty.NumberIntVal(1),
+			cty.ListVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("b"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.UnknownVal(cty.String),
+				}),
+			}),
+			false,
+		},
+		{
+			cty.UnknownVal(cty.List(cty.String)),
+			cty.NumberIntVal(1),
 			cty.UnknownVal(cty.List(cty.List(cty.String))),
 			false,
 		},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
-		t.Run(fmt.Sprintf("chunklist(%#v, %#v)", test.List, test.Size), func(t *testing.T) {
+		t.Run(fmt.Sprintf("%d-chunklist(%#v, %#v)", i, test.List, test.Size), func(t *testing.T) {
 			got, err := Chunklist(test.List, test.Size)
 
 			if test.Err {
@@ -1043,6 +1129,44 @@ func TestFlatten(t *testing.T) {
 			}),
 			false,
 		},
+		// handle single elements as arguments
+		{
+			cty.TupleVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("b"),
+				}),
+				cty.StringVal("c"),
+			}),
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+			}), false,
+		},
+		// handle single elements and mixed primitive types as arguments
+		{
+			cty.TupleVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("b"),
+				}),
+				cty.StringVal("c"),
+				cty.TupleVal([]cty.Value{
+					cty.StringVal("x"),
+					cty.NumberIntVal(1),
+				}),
+			}),
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.StringVal("c"),
+				cty.StringVal("x"),
+				cty.NumberIntVal(1),
+			}),
+			false,
+		},
+		// Primitive unknowns should still be flattened to a tuple
 		{
 			cty.ListVal([]cty.Value{
 				cty.ListVal([]cty.Value{
@@ -1054,8 +1178,26 @@ func TestFlatten(t *testing.T) {
 					cty.StringVal("d"),
 				}),
 			}),
-			cty.DynamicVal,
+			cty.TupleVal([]cty.Value{
-			false,
+				cty.StringVal("a"),
+				cty.StringVal("b"),
+				cty.UnknownVal(cty.String),
+				cty.StringVal("d"),
+			}), false,
+		},
+		// An unknown series should return an unknown dynamic value
+		{
+			cty.TupleVal([]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("b"),
+				}),
+				cty.TupleVal([]cty.Value{
+					cty.UnknownVal(cty.List(cty.String)),
+					cty.StringVal("d"),
+				}),
+			}),
+			cty.UnknownVal(cty.DynamicPseudoType), false,
 		},
 		{
 			cty.ListValEmpty(cty.String),
@@ -1102,8 +1244,8 @@ func TestFlatten(t *testing.T) {
 		},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
-		t.Run(fmt.Sprintf("flatten(%#v)", test.List), func(t *testing.T) {
+		t.Run(fmt.Sprintf("%d-flatten(%#v)", i, test.List), func(t *testing.T) {
 			got, err := Flatten(test.List)
 
 			if test.Err {
@@ -2354,6 +2496,11 @@ func TestSlice(t *testing.T) {
 		cty.StringVal("a"),
 		cty.UnknownVal(cty.String),
 	})
+	tuple := cty.TupleVal([]cty.Value{
+		cty.StringVal("a"),
+		cty.NumberIntVal(1),
+		cty.UnknownVal(cty.List(cty.String)),
+	})
 	tests := []struct {
 		List       cty.Value
 		StartIndex cty.Value
@@ -2370,10 +2517,24 @@ func TestSlice(t *testing.T) {
 			}),
 			false,
 		},
-		{ // unknowns in the list
+		{ // slice only an unknown value
 			listWithUnknowns,
 			cty.NumberIntVal(1),
 			cty.NumberIntVal(2),
+			cty.ListVal([]cty.Value{cty.UnknownVal(cty.String)}),
+			false,
+		},
+		{ // slice multiple values, which contain an unknown
+			listWithUnknowns,
+			cty.NumberIntVal(0),
+			cty.NumberIntVal(2),
+			listWithUnknowns,
+			false,
+		},
+		{ // an unknown list should be slicable, returning an unknown list
+			cty.UnknownVal(cty.List(cty.String)),
+			cty.NumberIntVal(0),
+			cty.NumberIntVal(2),
 			cty.UnknownVal(cty.List(cty.String)),
 			false,
 		},
@@ -2414,10 +2575,44 @@ func TestSlice(t *testing.T) {
 			cty.NilVal,
 			true,
 		},
+		{ // sets are not slice-able
+			cty.SetVal([]cty.Value{
+				cty.StringVal("x"),
+				cty.StringVal("y"),
+			}),
+			cty.NumberIntVal(0),
+			cty.NumberIntVal(0),
+			cty.NilVal,
+			true,
+		},
+		{ // tuple slice
+			tuple,
+			cty.NumberIntVal(1),
+			cty.NumberIntVal(3),
+			cty.TupleVal([]cty.Value{
+				cty.NumberIntVal(1),
+				cty.UnknownVal(cty.List(cty.String)),
+			}),
+			false,
+		},
+		{ // empty list slice
+			listOfStrings,
+			cty.NumberIntVal(2),
+			cty.NumberIntVal(2),
+			cty.ListValEmpty(cty.String),
+			false,
+		},
+		{ // empty tuple slice
+			tuple,
+			cty.NumberIntVal(3),
+			cty.NumberIntVal(3),
+			cty.EmptyTupleVal,
+			false,
+		},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
-		t.Run(fmt.Sprintf("slice(%#v, %#v, %#v)", test.List, test.StartIndex, test.EndIndex), func(t *testing.T) {
+		t.Run(fmt.Sprintf("%d-slice(%#v, %#v, %#v)", i, test.List, test.StartIndex, test.EndIndex), func(t *testing.T) {
 			got, err := Slice(test.List, test.StartIndex, test.EndIndex)
 
 			if test.Err {

lang/functions_test.go

@@ -155,7 +155,7 @@ func TestFunctions(t *testing.T) {
 
 			{
 				`coalescelist(["first", "second"], ["third", "fourth"])`,
-				cty.ListVal([]cty.Value{
+				cty.TupleVal([]cty.Value{
 					cty.StringVal("first"), cty.StringVal("second"),
 				}),
 			},
@@ -163,12 +163,19 @@ func TestFunctions(t *testing.T) {
 
 		"coalescelist": {
 			{
-				`coalescelist(["a", "b"], ["c", "d"])`,
+				`coalescelist(list("a", "b"), list("c", "d"))`,
 				cty.ListVal([]cty.Value{
 					cty.StringVal("a"),
 					cty.StringVal("b"),
 				}),
 			},
+			{
+				`coalescelist(["a", "b"], ["c", "d"])`,
+				cty.TupleVal([]cty.Value{
+					cty.StringVal("a"),
+					cty.StringVal("b"),
+				}),
+			},
 		},
 
 		"compact": {
@@ -592,11 +599,18 @@ func TestFunctions(t *testing.T) {
 
 		"slice": {
 			{
-				`slice(["a", "b", "c", "d"], 1, 3)`,
+				// force a list type here for testing
+				`slice(list("a", "b", "c", "d"), 1, 3)`,
 				cty.ListVal([]cty.Value{
 					cty.StringVal("b"), cty.StringVal("c"),
 				}),
 			},
+			{
+				`slice(["a", "b", 3, 4], 1, 3)`,
+				cty.TupleVal([]cty.Value{
+					cty.StringVal("b"), cty.NumberIntVal(3),
+				}),
+			},
 		},
 
 		"sort": {