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decode.go
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decode.go
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package literals
import (
"go/ast"
"go/constant"
"reflect"
"github.com/fatih/structtag"
"encr.dev/v2/internals/perr"
)
func Decode[T any](errs *perr.List, literal *Struct, defaultValues *T) T {
var decodeTo T
dst := reflect.ValueOf(&decodeTo)
if dst.Elem().Kind() != reflect.Struct {
errs.Assert(errArgumentMustBeStruct.AtGoNode(literal.ast))
}
dst = dst.Elem()
var defaultValue reflect.Value
if defaultValues != nil {
defaultValue = reflect.ValueOf(defaultValues).Elem()
}
fieldPaths := decodeStruct(errs, literal, dst, defaultValue)
decodedFields := make(map[string]bool)
for _, fp := range fieldPaths {
decodedFields[fp] = true
}
// Make sure all the fields we care about have been decoded and nothing else.
for _, f := range literal.FieldPaths() {
if !decodedFields[f] {
errs.Add(errUnexpectedField.AtGoNode(literal.Expr(f)))
}
}
return decodeTo
}
func decodeStruct(errs *perr.List, literal *Struct, dst reflect.Value, defaultValues reflect.Value) (fieldPaths []string) {
for i := 0; i < dst.NumField(); i++ {
fieldType := dst.Type().Field(i)
if fieldType.Anonymous {
errs.Assert(errAnonymousFieldsNotSupported)
} else if !ast.IsExported(fieldType.Name) {
errs.Assert(errUnexportedFieldsNotSupported)
}
var fieldDefault reflect.Value
if defaultValues.IsValid() {
fieldDefault = defaultValues.Field(i)
}
paths := decodeField(errs, literal, fieldType, dst.Field(i), fieldDefault)
fieldPaths = append(fieldPaths, paths...)
}
return fieldPaths
}
// decodeField decodes a single constant literal field.
// It reports the field path it decoded.
func decodeField(errs *perr.List, literal *Struct, fieldType reflect.StructField, field reflect.Value, defaultField reflect.Value) (fieldPaths []string) {
// Determine the path we want to find the field at
fieldPath := fieldType.Name
required := false
dynamicOK := false
zeroValueOK := false
useDefaultValue := false
tag, err := structtag.Parse(string(fieldType.Tag))
if err != nil {
errs.Assert(errInvalidTag.AtGoNode(literal.Expr(fieldPath)).Wrapping(err))
}
if tagOpts, err := tag.Get("literal"); err == nil {
if tagOpts.Name != "" {
fieldPath = tagOpts.Name
}
required = !tagOpts.HasOption("optional")
dynamicOK = tagOpts.HasOption("dynamic")
zeroValueOK = tagOpts.HasOption("zero-ok")
useDefaultValue = tagOpts.HasOption("default")
}
fieldPaths = []string{fieldPath}
// If the field is required and isn't set, return an error.
if isSet := literal.IsSet(fieldPath); !isSet {
if required {
pos := literal.Pos(fieldPath)
errs.Add(errMissingRequiredField(fieldPath).AtGoPos(pos, pos))
return
} else {
if useDefaultValue && defaultField.IsValid() {
// If the field is optional and we have a default value, use it.
field.Set(defaultField)
}
// Nothing to do
return
}
}
// If the field is not dynamic and we don't allow dynamic fields, return an error.
isDynamic := !literal.IsConstant(fieldPath)
if isDynamic && !dynamicOK {
errs.Add(errIsntConstant(fieldPath).AtGoNode(literal.Expr(fieldPath)))
return
} else if isDynamic {
// Make sure the type is Expr.
if field.Type().PkgPath() != "go/ast" || field.Type().Name() != "Expr" {
errs.Assert(errDyanmicFieldNotExpr.AtGoNode(literal.Expr(fieldPath)))
}
field.Set(reflect.ValueOf(literal.Expr(fieldPath)))
return
}
val := literal.ConstantValue(fieldPath)
switch fieldType.Type.Kind() {
case reflect.String:
if val.Kind() == constant.String {
field.SetString(constant.StringVal(val))
} else {
errs.Add(errWrongDynamicType(fieldPath, "string").AtGoNode(literal.Expr(fieldPath)))
}
case reflect.Int, reflect.Int64, reflect.Uint, reflect.Uint64:
if val.Kind() == constant.Int {
n, _ := constant.Int64Val(val)
field.SetInt(n)
} else {
errs.Add(errWrongDynamicType(fieldPath, "integer").AtGoNode(literal.Expr(fieldPath)))
}
case reflect.Bool:
if val.Kind() == constant.Bool {
field.SetBool(constant.BoolVal(val))
} else {
errs.Add(errWrongDynamicType(fieldPath, "boolean").AtGoNode(literal.Expr(fieldPath)))
}
case reflect.Struct:
child, ok := literal.ChildStruct(fieldPath)
if !ok {
errs.Add(errWrongDynamicType(fieldPath, "inline struct").AtGoNode(literal.Expr(fieldPath)))
return
}
childPaths := decodeStruct(errs, child, field, defaultField)
for _, p := range childPaths {
fieldPaths = append(fieldPaths, fieldPath+"."+p)
}
return fieldPaths
default:
errs.Assert(errUnsupportedType(fieldType.Type.Kind()).AtGoNode(literal.Expr(fieldPath)))
}
// Now that we've set the value, if the field is required make sure it's not the zero value.
if required && !zeroValueOK && field.IsZero() {
errs.Add(errZeroValue(fieldPath).AtGoNode(literal.Expr(fieldPath)))
}
return fieldPaths
}