Import functions from Terraform

cty/function/stdlib/conversion.go

@@ -0,0 +1,87 @@
+package stdlib
+
+import (
+	"strconv"
+
+	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/convert"
+	"github.com/zclconf/go-cty/cty/function"
+)
+
+// MakeToFunc constructs a "to..." function, like "tostring", which converts
+// its argument to a specific type or type kind.
+//
+// The given type wantTy can be any type constraint that cty's "convert" package
+// would accept. In particular, this means that you can pass
+// cty.List(cty.DynamicPseudoType) to mean "list of any single type", which
+// will then cause cty to attempt to unify all of the element types when given
+// a tuple.
+func MakeToFunc(wantTy cty.Type) function.Function {
+	return function.New(&function.Spec{
+		Params: []function.Parameter{
+			{
+				Name: "v",
+				// We use DynamicPseudoType rather than wantTy here so that
+				// all values will pass through the function API verbatim and
+				// we can handle the conversion logic within the Type and
+				// Impl functions. This allows us to customize the error
+				// messages to be more appropriate for an explicit type
+				// conversion, whereas the cty function system produces
+				// messages aimed at _implicit_ type conversions.
+				Type:      cty.DynamicPseudoType,
+				AllowNull: true,
+			},
+		},
+		Type: func(args []cty.Value) (cty.Type, error) {
+			gotTy := args[0].Type()
+			if gotTy.Equals(wantTy) {
+				return wantTy, nil
+			}
+			conv := convert.GetConversionUnsafe(args[0].Type(), wantTy)
+			if conv == nil {
+				// We'll use some specialized errors for some trickier cases,
+				// but most we can handle in a simple way.
+				switch {
+				case gotTy.IsTupleType() && wantTy.IsTupleType():
+					return cty.NilType, function.NewArgErrorf(0, "incompatible tuple type for conversion: %s", convert.MismatchMessage(gotTy, wantTy))
+				case gotTy.IsObjectType() && wantTy.IsObjectType():
+					return cty.NilType, function.NewArgErrorf(0, "incompatible object type for conversion: %s", convert.MismatchMessage(gotTy, wantTy))
+				default:
+					return cty.NilType, function.NewArgErrorf(0, "cannot convert %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
+				}
+			}
+			// If a conversion is available then everything is fine.
+			return wantTy, nil
+		},
+		Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
+			// We didn't set "AllowUnknown" on our argument, so it is guaranteed
+			// to be known here but may still be null.
+			ret, err := convert.Convert(args[0], retType)
+			if err != nil {
+				// Because we used GetConversionUnsafe above, conversion can
+				// still potentially fail in here. For example, if the user
+				// asks to convert the string "a" to bool then we'll
+				// optimistically permit it during type checking but fail here
+				// once we note that the value isn't either "true" or "false".
+				gotTy := args[0].Type()
+				switch {
+				case gotTy == cty.String && wantTy == cty.Bool:
+					what := "string"
+					if !args[0].IsNull() {
+						what = strconv.Quote(args[0].AsString())
+					}
+					return cty.NilVal, function.NewArgErrorf(0, `cannot convert %s to bool; only the strings "true" or "false" are allowed`, what)
+				case gotTy == cty.String && wantTy == cty.Number:
+					what := "string"
+					if !args[0].IsNull() {
+						what = strconv.Quote(args[0].AsString())
+					}
+					return cty.NilVal, function.NewArgErrorf(0, `cannot convert %s to number; given string must be a decimal representation of a number`, what)
+				default:
+					return cty.NilVal, function.NewArgErrorf(0, "cannot convert %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
+				}
+			}
+			return ret, nil
+		},
+	})
+}

cty/function/stdlib/conversion_test.go

@@ -0,0 +1,131 @@
+package stdlib
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func TestTo(t *testing.T) {
+	tests := []struct {
+		Value    cty.Value
+		TargetTy cty.Type
+		Want     cty.Value
+		Err      string
+	}{
+		{
+			cty.StringVal("a"),
+			cty.String,
+			cty.StringVal("a"),
+			``,
+		},
+		{
+			cty.UnknownVal(cty.String),
+			cty.String,
+			cty.UnknownVal(cty.String),
+			``,
+		},
+		{
+			cty.NullVal(cty.String),
+			cty.String,
+			cty.NullVal(cty.String),
+			``,
+		},
+		{
+			cty.True,
+			cty.String,
+			cty.StringVal("true"),
+			``,
+		},
+		{
+			cty.StringVal("a"),
+			cty.Bool,
+			cty.DynamicVal,
+			`cannot convert "a" to bool; only the strings "true" or "false" are allowed`,
+		},
+		{
+			cty.StringVal("a"),
+			cty.Number,
+			cty.DynamicVal,
+			`cannot convert "a" to number; given string must be a decimal representation of a number`,
+		},
+		{
+			cty.NullVal(cty.String),
+			cty.Number,
+			cty.NullVal(cty.Number),
+			``,
+		},
+		{
+			cty.UnknownVal(cty.Bool),
+			cty.String,
+			cty.UnknownVal(cty.String),
+			``,
+		},
+		{
+			cty.UnknownVal(cty.String),
+			cty.Bool,
+			cty.UnknownVal(cty.Bool), // conversion is optimistic
+			``,
+		},
+		{
+			cty.TupleVal([]cty.Value{cty.StringVal("hello"), cty.True}),
+			cty.List(cty.String),
+			cty.ListVal([]cty.Value{cty.StringVal("hello"), cty.StringVal("true")}),
+			``,
+		},
+		{
+			cty.TupleVal([]cty.Value{cty.StringVal("hello"), cty.True}),
+			cty.Set(cty.String),
+			cty.SetVal([]cty.Value{cty.StringVal("hello"), cty.StringVal("true")}),
+			``,
+		},
+		{
+			cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("hello"), "bar": cty.True}),
+			cty.Map(cty.String),
+			cty.MapVal(map[string]cty.Value{"foo": cty.StringVal("hello"), "bar": cty.StringVal("true")}),
+			``,
+		},
+		{
+			cty.EmptyTupleVal,
+			cty.String,
+			cty.DynamicVal,
+			`cannot convert tuple to string`,
+		},
+		{
+			cty.UnknownVal(cty.EmptyTuple),
+			cty.String,
+			cty.DynamicVal,
+			`cannot convert tuple to string`,
+		},
+		{
+			cty.EmptyObjectVal,
+			cty.Object(map[string]cty.Type{"foo": cty.String}),
+			cty.DynamicVal,
+			`incompatible object type for conversion: attribute "foo" is required`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("to %s(%#v)", test.TargetTy.FriendlyNameForConstraint(), test.Value), func(t *testing.T) {
+			f := MakeToFunc(test.TargetTy)
+			got, err := f.Call([]cty.Value{test.Value})
+
+			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)
+			}
+		})
+	}
+}

cty/function/stdlib/datetime.go

@@ -203,6 +203,33 @@ var FormatDateFunc = function.New(&function.Spec{
 	},
 })
 
+// TimeAddFunc is a function that adds a duration to a timestamp, returning a new timestamp.
+var TimeAddFunc = function.New(&function.Spec{
+	Params: []function.Parameter{
+		{
+			Name: "timestamp",
+			Type: cty.String,
+		},
+		{
+			Name: "duration",
+			Type: cty.String,
+		},
+	},
+	Type: function.StaticReturnType(cty.String),
+	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
+		ts, err := time.Parse(time.RFC3339, args[0].AsString())
+		if err != nil {
+			return cty.UnknownVal(cty.String), err
+		}
+		duration, err := time.ParseDuration(args[1].AsString())
+		if err != nil {
+			return cty.UnknownVal(cty.String), err
+		}
+
+		return cty.StringVal(ts.Add(duration).Format(time.RFC3339)), nil
+	},
+})
+
 // FormatDate reformats a timestamp given in RFC3339 syntax into another time
 // syntax defined by a given format string.
 //
@@ -383,3 +410,20 @@ func splitDateFormat(data []byte, atEOF bool) (advance int, token []byte, err er
 func startsDateFormatVerb(b byte) bool {
 	return (b >= 'a' && b <= 'z') || (b >= 'A' && b <= 'Z')
 }
+
+// TimeAdd adds a duration to a timestamp, returning a new timestamp.
+//
+// In the HCL language, timestamps are conventionally represented as
+// strings using RFC 3339 "Date and Time format" syntax. Timeadd requires
+// the timestamp argument to be a string conforming to this syntax.
+//
+// `duration` is a string representation of a time difference, consisting of
+// sequences of number and unit pairs, like `"1.5h"` or `1h30m`. The accepted
+// units are `ns`, `us` (or `µs`), `"ms"`, `"s"`, `"m"`, and `"h"`. The first
+// number may be negative to indicate a negative duration, like `"-2h5m"`.
+//
+// The result is a string, also in RFC 3339 format, representing the result
+// of adding the given direction to the given timestamp.
+func TimeAdd(timestamp cty.Value, duration cty.Value) (cty.Value, error) {
+	return TimeAddFunc.Call([]cty.Value{timestamp, duration})
+}