lang: Improved robustness of sum function

Fixes error when calling sum with values not known until apply time.
Also allows sum to cope with numbers too large to represent in float64,
along with correctly handling errors when trying to sum opposing
infinities.

lang/funcs/collection.go

@@ -3,13 +3,13 @@ package funcs
 import (
 	"errors"
 	"fmt"
+	"math/big"
 	"sort"
 
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/convert"
 	"github.com/zclconf/go-cty/cty/function"
 	"github.com/zclconf/go-cty/cty/function/stdlib"
-	"github.com/zclconf/go-cty/cty/gocty"
 )
 
 var LengthFunc = function.New(&function.Spec{
@@ -404,27 +404,45 @@ var SumFunc = function.New(&function.Spec{
 		arg := args[0].AsValueSlice()
 		ty := args[0].Type()
 
-		var i float64
-		var s float64
-
 		if !ty.IsListType() && !ty.IsSetType() && !ty.IsTupleType() {
 			return cty.NilVal, function.NewArgErrorf(0, fmt.Sprintf("argument must be list, set, or tuple. Received %s", ty.FriendlyName()))
 		}
 
-		if !args[0].IsKnown() {
+		if !args[0].IsWhollyKnown() {
 			return cty.UnknownVal(cty.Number), nil
 		}
 
-		for _, v := range arg {
+		// big.Float.Add can panic if the input values are opposing infinities,
-
+		// so we must catch that here in order to remain within
-			if err := gocty.FromCtyValue(v, &i); err != nil {
+		// the cty Function abstraction.
-				return cty.UnknownVal(cty.Number), function.NewArgErrorf(0, "argument must be list, set, or tuple of number values")
+		defer func() {
-			} else {
+			if r := recover(); r != nil {
-				s += i
+				if _, ok := r.(big.ErrNaN); ok {
+					ret = cty.NilVal
+					err = fmt.Errorf("can't compute sum of opposing infinities")
+				} else {
+					// not a panic we recognize
+					panic(r)
+				}
 			}
+		}()
+
+		s := arg[0]
+		if s.IsNull() {
+			return cty.NilVal, function.NewArgErrorf(0, "argument must be list, set, or tuple of number values")
+		}
+		for _, v := range arg[1:] {
+			if v.IsNull() {
+				return cty.NilVal, function.NewArgErrorf(0, "argument must be list, set, or tuple of number values")
+			}
+			v, err = convert.Convert(v, cty.Number)
+			if err != nil {
+				return cty.NilVal, function.NewArgErrorf(0, "argument must be list, set, or tuple of number values")
+			}
+			s = s.Add(v)
 		}
 
-		return cty.NumberFloatVal(s), nil
+		return s, nil
 	},
 })
 

lang/funcs/collection_test.go

@@ -2,6 +2,7 @@ package funcs
 
 import (
 	"fmt"
+	"math"
 	"testing"
 
 	"github.com/zclconf/go-cty/cty"
@@ -996,7 +997,7 @@ func TestSum(t *testing.T) {
 	tests := []struct {
 		List cty.Value
 		Want cty.Value
-		Err  bool
+		Err  string
 	}{
 		{
 			cty.ListVal([]cty.Value{
@@ -1005,7 +1006,7 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(3),
 			}),
 			cty.NumberIntVal(6),
-			false,
+			"",
 		},
 		{
 			cty.ListVal([]cty.Value{
@@ -1016,7 +1017,7 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(234),
 			}),
 			cty.NumberIntVal(66685532),
-			false,
+			"",
 		},
 		{
 			cty.ListVal([]cty.Value{
@@ -1025,7 +1026,7 @@ func TestSum(t *testing.T) {
 				cty.StringVal("c"),
 			}),
 			cty.UnknownVal(cty.String),
-			true,
+			"argument must be list, set, or tuple of number values",
 		},
 		{
 			cty.ListVal([]cty.Value{
@@ -1034,7 +1035,7 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(5),
 			}),
 			cty.NumberIntVal(-4),
-			false,
+			"",
 		},
 		{
 			cty.ListVal([]cty.Value{
@@ -1043,7 +1044,7 @@ func TestSum(t *testing.T) {
 				cty.NumberFloatVal(5.7),
 			}),
 			cty.NumberFloatVal(35.3),
-			false,
+			"",
 		},
 		{
 			cty.ListVal([]cty.Value{
@@ -1052,12 +1053,20 @@ func TestSum(t *testing.T) {
 				cty.NumberFloatVal(-5.7),
 			}),
 			cty.NumberFloatVal(-35.3),
-			false,
+			"",
 		},
 		{
 			cty.ListVal([]cty.Value{cty.NullVal(cty.Number)}),
 			cty.NilVal,
-			true,
+			"argument must be list, set, or tuple of number values",
+		},
+		{
+			cty.ListVal([]cty.Value{
+				cty.NumberIntVal(5),
+				cty.NullVal(cty.Number),
+			}),
+			cty.NilVal,
+			"argument must be list, set, or tuple of number values",
 		},
 		{
 			cty.SetVal([]cty.Value{
@@ -1066,7 +1075,7 @@ func TestSum(t *testing.T) {
 				cty.StringVal("c"),
 			}),
 			cty.UnknownVal(cty.String),
-			true,
+			"argument must be list, set, or tuple of number values",
 		},
 		{
 			cty.SetVal([]cty.Value{
@@ -1075,7 +1084,7 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(5),
 			}),
 			cty.NumberIntVal(-4),
-			false,
+			"",
 		},
 		{
 			cty.SetVal([]cty.Value{
@@ -1084,7 +1093,7 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(30),
 			}),
 			cty.NumberIntVal(65),
-			false,
+			"",
 		},
 		{
 			cty.SetVal([]cty.Value{
@@ -1093,14 +1102,14 @@ func TestSum(t *testing.T) {
 				cty.NumberFloatVal(3),
 			}),
 			cty.NumberFloatVal(2354),
-			false,
+			"",
 		},
 		{
 			cty.SetVal([]cty.Value{
 				cty.NumberFloatVal(2),
 			}),
 			cty.NumberFloatVal(2),
-			false,
+			"",
 		},
 		{
 			cty.SetVal([]cty.Value{
@@ -1111,7 +1120,7 @@ func TestSum(t *testing.T) {
 				cty.NumberFloatVal(-4),
 			}),
 			cty.NumberFloatVal(-199),
-			false,
+			"",
 		},
 		{
 			cty.TupleVal([]cty.Value{
@@ -1120,27 +1129,53 @@ func TestSum(t *testing.T) {
 				cty.NumberIntVal(38),
 			}),
 			cty.UnknownVal(cty.String),
-			true,
+			"argument must be list, set, or tuple of number values",
 		},
 		{
 			cty.NumberIntVal(12),
 			cty.NilVal,
-			true,
+			"cannot sum noniterable",
 		},
 		{
 			cty.ListValEmpty(cty.Number),
 			cty.NilVal,
-			true,
+			"cannot sum an empty list",
 		},
 		{
 			cty.MapVal(map[string]cty.Value{"hello": cty.True}),
 			cty.NilVal,
-			true,
+			"argument must be list, set, or tuple. Received map of bool",
 		},
 		{
 			cty.UnknownVal(cty.Number),
 			cty.UnknownVal(cty.Number),
-			false,
+			"",
+		},
+		{
+			cty.UnknownVal(cty.List(cty.Number)),
+			cty.UnknownVal(cty.Number),
+			"",
+		},
+		{ // known list containing unknown values
+			cty.ListVal([]cty.Value{cty.UnknownVal(cty.Number)}),
+			cty.UnknownVal(cty.Number),
+			"",
+		},
+		{ // numbers too large to represent as float64
+			cty.ListVal([]cty.Value{
+				cty.MustParseNumberVal("1e+500"),
+				cty.MustParseNumberVal("1e+500"),
+			}),
+			cty.MustParseNumberVal("2e+500"),
+			"",
+		},
+		{ // edge case we have a special error handler for
+			cty.ListVal([]cty.Value{
+				cty.NumberFloatVal(math.Inf(1)),
+				cty.NumberFloatVal(math.Inf(-1)),
+			}),
+			cty.NilVal,
+			"can't compute sum of opposing infinities",
 		},
 	}
 
@@ -1148,9 +1183,11 @@ func TestSum(t *testing.T) {
 		t.Run(fmt.Sprintf("sum(%#v)", test.List), func(t *testing.T) {
 			got, err := Sum(test.List)
 
-			if test.Err {
+			if test.Err != "" {
 				if err == nil {
 					t.Fatal("succeeded; want error")
+				} else if got, want := err.Error(), test.Err; got != want {
+					t.Fatalf("wrong error\n got: %s\nwant: %s", got, want)
 				}
 				return
 			} else if err != nil {