terraform/internal/lang/funcs/conversion.go

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package funcs
import (
"fmt"
"sort"
"strconv"
"strings"
"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,
AllowMarked: 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 args[0].ContainsMarked():
// Generic message so we won't inadvertently disclose
// information about sensitive values.
return cty.NilVal, function.NewArgErrorf(0, "cannot convert this sensitive %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
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
},
})
}
var TypeFunc = function.New(&function.Spec{
Params: []function.Parameter{
{
Name: "value",
Type: cty.DynamicPseudoType,
AllowDynamicType: true,
AllowUnknown: true,
AllowNull: true,
},
},
Type: function.StaticReturnType(cty.String),
Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
return cty.StringVal(TypeString(args[0].Type())).Mark("raw"), nil
},
})
// Modified copy of TypeString from go-cty:
// https://github.com/zclconf/go-cty-debug/blob/master/ctydebug/type_string.go
//
// TypeString returns a string representation of a given type that is
// reminiscent of Go syntax calling into the cty package but is mainly
// intended for easy human inspection of values in tests, debug output, etc.
//
// The resulting string will include newlines and indentation in order to
// increase the readability of complex structures. It always ends with a
// newline, so you can print this result directly to your output.
func TypeString(ty cty.Type) string {
var b strings.Builder
writeType(ty, &b, 0)
return b.String()
}
func writeType(ty cty.Type, b *strings.Builder, indent int) {
switch {
case ty == cty.NilType:
b.WriteString("nil")
return
case ty.IsObjectType():
atys := ty.AttributeTypes()
if len(atys) == 0 {
b.WriteString("object({})")
return
}
attrNames := make([]string, 0, len(atys))
for name := range atys {
attrNames = append(attrNames, name)
}
sort.Strings(attrNames)
b.WriteString("object({\n")
indent++
for _, name := range attrNames {
aty := atys[name]
b.WriteString(indentSpaces(indent))
fmt.Fprintf(b, "%s: ", name)
writeType(aty, b, indent)
b.WriteString(",\n")
}
indent--
b.WriteString(indentSpaces(indent))
b.WriteString("})")
case ty.IsTupleType():
etys := ty.TupleElementTypes()
if len(etys) == 0 {
b.WriteString("tuple([])")
return
}
b.WriteString("tuple([\n")
indent++
for _, ety := range etys {
b.WriteString(indentSpaces(indent))
writeType(ety, b, indent)
b.WriteString(",\n")
}
indent--
b.WriteString(indentSpaces(indent))
b.WriteString("])")
case ty.IsCollectionType():
ety := ty.ElementType()
switch {
case ty.IsListType():
b.WriteString("list(")
case ty.IsMapType():
b.WriteString("map(")
case ty.IsSetType():
b.WriteString("set(")
default:
// At the time of writing there are no other collection types,
// but we'll be robust here and just pass through the GoString
// of anything we don't recognize.
b.WriteString(ty.FriendlyName())
return
}
// Because object and tuple types render split over multiple
// lines, a collection type container around them can end up
// being hard to see when scanning, so we'll generate some extra
// indentation to make a collection of structural type more visually
// distinct from the structural type alone.
complexElem := ety.IsObjectType() || ety.IsTupleType()
if complexElem {
indent++
b.WriteString("\n")
b.WriteString(indentSpaces(indent))
}
writeType(ty.ElementType(), b, indent)
if complexElem {
indent--
b.WriteString(",\n")
b.WriteString(indentSpaces(indent))
}
b.WriteString(")")
default:
// For any other type we'll just use its GoString and assume it'll
// follow the usual GoString conventions.
b.WriteString(ty.FriendlyName())
}
}
func indentSpaces(level int) string {
return strings.Repeat(" ", level)
}
func Type(input []cty.Value) (cty.Value, error) {
return TypeFunc.Call(input)
}