175 lines
4.0 KiB
Go
175 lines
4.0 KiB
Go
package gohcl
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import (
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"fmt"
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"reflect"
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"sort"
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"strings"
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"github.com/hashicorp/hcl2/hcl"
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)
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// ImpliedBodySchema produces a hcl.BodySchema derived from the type of the
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// given value, which must be a struct value or a pointer to one. If an
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// inappropriate value is passed, this function will panic.
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//
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// The second return argument indicates whether the given struct includes
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// a "remain" field, and thus the returned schema is non-exhaustive.
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//
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// This uses the tags on the fields of the struct to discover how each
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// field's value should be expressed within configuration. If an invalid
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// mapping is attempted, this function will panic.
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func ImpliedBodySchema(val interface{}) (schema *hcl.BodySchema, partial bool) {
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ty := reflect.TypeOf(val)
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if ty.Kind() == reflect.Ptr {
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ty = ty.Elem()
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}
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if ty.Kind() != reflect.Struct {
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panic(fmt.Sprintf("given value must be struct, not %T", val))
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}
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var attrSchemas []hcl.AttributeSchema
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var blockSchemas []hcl.BlockHeaderSchema
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tags := getFieldTags(ty)
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attrNames := make([]string, 0, len(tags.Attributes))
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for n := range tags.Attributes {
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attrNames = append(attrNames, n)
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}
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sort.Strings(attrNames)
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for _, n := range attrNames {
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idx := tags.Attributes[n]
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optional := tags.Optional[n]
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field := ty.Field(idx)
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var required bool
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switch {
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case field.Type.AssignableTo(exprType):
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// If we're decoding to hcl.Expression then absense can be
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// indicated via a null value, so we don't specify that
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// the field is required during decoding.
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required = false
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case field.Type.Kind() != reflect.Ptr && !optional:
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required = true
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default:
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required = false
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}
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attrSchemas = append(attrSchemas, hcl.AttributeSchema{
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Name: n,
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Required: required,
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})
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}
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blockNames := make([]string, 0, len(tags.Blocks))
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for n := range tags.Blocks {
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blockNames = append(blockNames, n)
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}
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sort.Strings(blockNames)
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for _, n := range blockNames {
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idx := tags.Blocks[n]
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field := ty.Field(idx)
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fty := field.Type
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if fty.Kind() == reflect.Slice {
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fty = fty.Elem()
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}
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if fty.Kind() == reflect.Ptr {
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fty = fty.Elem()
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}
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if fty.Kind() != reflect.Struct {
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panic(fmt.Sprintf(
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"hcl 'block' tag kind cannot be applied to %s field %s: struct required", field.Type.String(), field.Name,
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))
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}
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ftags := getFieldTags(fty)
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var labelNames []string
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if len(ftags.Labels) > 0 {
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labelNames = make([]string, len(ftags.Labels))
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for i, l := range ftags.Labels {
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labelNames[i] = l.Name
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}
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}
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blockSchemas = append(blockSchemas, hcl.BlockHeaderSchema{
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Type: n,
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LabelNames: labelNames,
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})
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}
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partial = tags.Remain != nil
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schema = &hcl.BodySchema{
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Attributes: attrSchemas,
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Blocks: blockSchemas,
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}
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return schema, partial
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}
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type fieldTags struct {
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Attributes map[string]int
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Blocks map[string]int
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Labels []labelField
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Remain *int
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Optional map[string]bool
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}
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type labelField struct {
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FieldIndex int
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Name string
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}
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func getFieldTags(ty reflect.Type) *fieldTags {
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ret := &fieldTags{
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Attributes: map[string]int{},
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Blocks: map[string]int{},
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Optional: map[string]bool{},
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}
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ct := ty.NumField()
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for i := 0; i < ct; i++ {
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field := ty.Field(i)
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tag := field.Tag.Get("hcl")
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if tag == "" {
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continue
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}
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comma := strings.Index(tag, ",")
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var name, kind string
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if comma != -1 {
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name = tag[:comma]
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kind = tag[comma+1:]
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} else {
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name = tag
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kind = "attr"
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}
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switch kind {
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case "attr":
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ret.Attributes[name] = i
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case "block":
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ret.Blocks[name] = i
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case "label":
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ret.Labels = append(ret.Labels, labelField{
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FieldIndex: i,
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Name: name,
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})
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case "remain":
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if ret.Remain != nil {
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panic("only one 'remain' tag is permitted")
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}
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idx := i // copy, because this loop will continue assigning to i
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ret.Remain = &idx
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case "optional":
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ret.Attributes[name] = i
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ret.Optional[name] = true
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default:
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panic(fmt.Sprintf("invalid hcl field tag kind %q on %s %q", kind, field.Type.String(), field.Name))
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}
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}
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return ret
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}
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