Library to convert config.Value to Go struct (#904)

## Changes

Now that we have a new YAML loader (see #828), we need code to turn this
into our Go structs.

## Tests

New unit tests pass.

Confirmed that we can replace our existing loader/converter with this
one and that existing unit tests for bundle loading still pass.

libs/config/convert/error.go

@@ -0,0 +1,16 @@
+package convert
+
+import (
+	"fmt"
+
+	"github.com/databricks/cli/libs/config"
+)
+
+type TypeError struct {
+	value config.Value
+	msg   string
+}
+
+func (e TypeError) Error() string {
+	return fmt.Sprintf("%s: %s", e.value.Location(), e.msg)
+}

libs/config/convert/struct_info.go

@@ -0,0 +1,87 @@
+package convert
+
+import (
+	"reflect"
+	"strings"
+	"sync"
+)
+
+// structInfo holds the type information we need to efficiently
+// convert data from a [config.Value] to a Go struct.
+type structInfo struct {
+	// Fields maps the JSON-name of the field to the field's index for use with [FieldByIndex].
+	Fields map[string][]int
+}
+
+// structInfoCache caches type information.
+var structInfoCache = make(map[reflect.Type]structInfo)
+
+// structInfoCacheLock guards concurrent access to structInfoCache.
+var structInfoCacheLock sync.Mutex
+
+// getStructInfo returns the [structInfo] for the given type.
+// It lazily populates a cache, so the first call for a given
+// type is slower than subsequent calls for that same type.
+func getStructInfo(typ reflect.Type) structInfo {
+	structInfoCacheLock.Lock()
+	defer structInfoCacheLock.Unlock()
+
+	si, ok := structInfoCache[typ]
+	if !ok {
+		si = buildStructInfo(typ)
+		structInfoCache[typ] = si
+	}
+
+	return si
+}
+
+// buildStructInfo populates a new [structInfo] for the given type.
+func buildStructInfo(typ reflect.Type) structInfo {
+	var out = structInfo{
+		Fields: make(map[string][]int),
+	}
+
+	// Queue holds the indexes of the structs to visit.
+	// It is initialized with a single empty slice to visit the top level struct.
+	var queue [][]int = [][]int{{}}
+	for i := 0; i < len(queue); i++ {
+		prefix := queue[i]
+
+		// Traverse embedded anonymous types (if prefix is non-empty).
+		styp := typ
+		if len(prefix) > 0 {
+			styp = styp.FieldByIndex(prefix).Type
+		}
+
+		// Dereference pointer type.
+		if styp.Kind() == reflect.Pointer {
+			styp = styp.Elem()
+		}
+
+		nf := styp.NumField()
+		for j := 0; j < nf; j++ {
+			sf := styp.Field(j)
+
+			// Recurse into anonymous fields.
+			if sf.Anonymous {
+				queue = append(queue, append(prefix, sf.Index...))
+				continue
+			}
+
+			name, _, _ := strings.Cut(sf.Tag.Get("json"), ",")
+			if name == "" || name == "-" {
+				continue
+			}
+
+			// Top level fields always take precedence.
+			// Therefore, if it is already set, we ignore it.
+			if _, ok := out.Fields[name]; ok {
+				continue
+			}
+
+			out.Fields[name] = append(prefix, sf.Index...)
+		}
+	}
+
+	return out
+}

libs/config/convert/struct_info_test.go

@@ -0,0 +1,89 @@
+package convert
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStructInfoPlain(t *testing.T) {
+	type Tmp struct {
+		Foo string `json:"foo"`
+		Bar string `json:"bar,omitempty"`
+
+		// Baz must be skipped.
+		Baz string `json:""`
+
+		// Qux must be skipped.
+		Qux string `json:"-"`
+	}
+
+	si := getStructInfo(reflect.TypeOf(Tmp{}))
+	assert.Len(t, si.Fields, 2)
+	assert.Equal(t, []int{0}, si.Fields["foo"])
+	assert.Equal(t, []int{1}, si.Fields["bar"])
+}
+
+func TestStructInfoAnonymousByValue(t *testing.T) {
+	type Bar struct {
+		Bar string `json:"bar"`
+	}
+
+	type Foo struct {
+		Foo string `json:"foo"`
+		Bar
+	}
+
+	type Tmp struct {
+		Foo
+	}
+
+	si := getStructInfo(reflect.TypeOf(Tmp{}))
+	assert.Len(t, si.Fields, 2)
+	assert.Equal(t, []int{0, 0}, si.Fields["foo"])
+	assert.Equal(t, []int{0, 1, 0}, si.Fields["bar"])
+}
+
+func TestStructInfoAnonymousByValuePrecedence(t *testing.T) {
+	type Bar struct {
+		Bar string `json:"bar"`
+	}
+
+	type Foo struct {
+		Foo string `json:"foo"`
+		Bar
+	}
+
+	type Tmp struct {
+		// "foo" comes from [Foo].
+		Foo
+		// "bar" comes from [Bar] directly, not through [Foo].
+		Bar
+	}
+
+	si := getStructInfo(reflect.TypeOf(Tmp{}))
+	assert.Len(t, si.Fields, 2)
+	assert.Equal(t, []int{0, 0}, si.Fields["foo"])
+	assert.Equal(t, []int{1, 0}, si.Fields["bar"])
+}
+
+func TestStructInfoAnonymousByPointer(t *testing.T) {
+	type Bar struct {
+		Bar string `json:"bar"`
+	}
+
+	type Foo struct {
+		Foo string `json:"foo"`
+		*Bar
+	}
+
+	type Tmp struct {
+		*Foo
+	}
+
+	si := getStructInfo(reflect.TypeOf(Tmp{}))
+	assert.Len(t, si.Fields, 2)
+	assert.Equal(t, []int{0, 0}, si.Fields["foo"])
+	assert.Equal(t, []int{0, 1, 0}, si.Fields["bar"])
+}

libs/config/convert/to_typed.go

@@ -0,0 +1,224 @@
+package convert
+
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+
+	"github.com/databricks/cli/libs/config"
+)
+
+func ToTyped(dst any, src config.Value) error {
+	dstv := reflect.ValueOf(dst)
+
+	// Dereference pointer if necessary
+	for dstv.Kind() == reflect.Pointer {
+		if dstv.IsNil() {
+			dstv.Set(reflect.New(dstv.Type().Elem()))
+		}
+		dstv = dstv.Elem()
+	}
+
+	// Verify that vv is settable.
+	if !dstv.CanSet() {
+		panic("cannot set destination value")
+	}
+
+	switch dstv.Kind() {
+	case reflect.Struct:
+		return toTypedStruct(dstv, src)
+	case reflect.Map:
+		return toTypedMap(dstv, src)
+	case reflect.Slice:
+		return toTypedSlice(dstv, src)
+	case reflect.String:
+		return toTypedString(dstv, src)
+	case reflect.Bool:
+		return toTypedBool(dstv, src)
+	case reflect.Int, reflect.Int32, reflect.Int64:
+		return toTypedInt(dstv, src)
+	case reflect.Float32, reflect.Float64:
+		return toTypedFloat(dstv, src)
+	}
+
+	return fmt.Errorf("unsupported type: %s", dstv.Kind())
+}
+
+func toTypedStruct(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindMap:
+		info := getStructInfo(dst.Type())
+		for k, v := range src.MustMap() {
+			index, ok := info.Fields[k]
+			if !ok {
+				// Ignore unknown fields.
+				// A warning will be printed later. See PR #904.
+				continue
+			}
+
+			// Create intermediate structs embedded as pointer types.
+			// Code inspired by [reflect.FieldByIndex] implementation.
+			f := dst
+			for i, x := range index {
+				if i > 0 {
+					if f.Kind() == reflect.Pointer {
+						if f.IsNil() {
+							f.Set(reflect.New(f.Type().Elem()))
+						}
+						f = f.Elem()
+					}
+				}
+				f = f.Field(x)
+			}
+
+			err := ToTyped(f.Addr().Interface(), v)
+			if err != nil {
+				return err
+			}
+		}
+
+		return nil
+	case config.KindNil:
+		dst.SetZero()
+		return nil
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a map, found a %s", src.Kind()),
+	}
+}
+
+func toTypedMap(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindMap:
+		m := src.MustMap()
+
+		// Always overwrite.
+		dst.Set(reflect.MakeMapWithSize(dst.Type(), len(m)))
+		for k, v := range m {
+			kv := reflect.ValueOf(k)
+			vv := reflect.New(dst.Type().Elem())
+			err := ToTyped(vv.Interface(), v)
+			if err != nil {
+				return err
+			}
+			dst.SetMapIndex(kv, vv.Elem())
+		}
+		return nil
+	case config.KindNil:
+		dst.SetZero()
+		return nil
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a map, found a %s", src.Kind()),
+	}
+}
+
+func toTypedSlice(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindSequence:
+		seq := src.MustSequence()
+
+		// Always overwrite.
+		dst.Set(reflect.MakeSlice(dst.Type(), len(seq), len(seq)))
+		for i := range seq {
+			err := ToTyped(dst.Index(i).Addr().Interface(), seq[i])
+			if err != nil {
+				return err
+			}
+		}
+		return nil
+	case config.KindNil:
+		dst.SetZero()
+		return nil
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a sequence, found a %s", src.Kind()),
+	}
+}
+
+func toTypedString(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindString:
+		dst.SetString(src.MustString())
+		return nil
+	case config.KindBool:
+		dst.SetString(strconv.FormatBool(src.MustBool()))
+		return nil
+	case config.KindInt:
+		dst.SetString(strconv.FormatInt(src.MustInt(), 10))
+		return nil
+	case config.KindFloat:
+		dst.SetString(strconv.FormatFloat(src.MustFloat(), 'f', -1, 64))
+		return nil
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a string, found a %s", src.Kind()),
+	}
+}
+
+func toTypedBool(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindBool:
+		dst.SetBool(src.MustBool())
+		return nil
+	case config.KindString:
+		// See https://github.com/go-yaml/yaml/blob/f6f7691b1fdeb513f56608cd2c32c51f8194bf51/decode.go#L684-L693.
+		switch src.MustString() {
+		case "y", "Y", "yes", "Yes", "YES", "on", "On", "ON":
+			dst.SetBool(true)
+			return nil
+		case "n", "N", "no", "No", "NO", "off", "Off", "OFF":
+			dst.SetBool(false)
+			return nil
+		}
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a boolean, found a %s", src.Kind()),
+	}
+}
+
+func toTypedInt(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindInt:
+		dst.SetInt(src.MustInt())
+		return nil
+	case config.KindString:
+		if i64, err := strconv.ParseInt(src.MustString(), 10, 64); err == nil {
+			dst.SetInt(i64)
+			return nil
+		}
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected an int, found a %s", src.Kind()),
+	}
+}
+
+func toTypedFloat(dst reflect.Value, src config.Value) error {
+	switch src.Kind() {
+	case config.KindFloat:
+		dst.SetFloat(src.MustFloat())
+		return nil
+	case config.KindString:
+		if f64, err := strconv.ParseFloat(src.MustString(), 64); err == nil {
+			dst.SetFloat(f64)
+			return nil
+		}
+	}
+
+	return TypeError{
+		value: src,
+		msg:   fmt.Sprintf("expected a float, found a %s", src.Kind()),
+	}
+}

libs/config/convert/to_typed_test.go

@@ -0,0 +1,430 @@
+package convert
+
+import (
+	"testing"
+
+	"github.com/databricks/cli/libs/config"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestToTypedStruct(t *testing.T) {
+	type Tmp struct {
+		Foo string `json:"foo"`
+		Bar string `json:"bar,omitempty"`
+
+		// Baz must be skipped.
+		Baz string `json:""`
+
+		// Qux must be skipped.
+		Qux string `json:"-"`
+	}
+
+	var out Tmp
+	v := config.V(map[string]config.Value{
+		"foo": config.V("bar"),
+		"bar": config.V("baz"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Equal(t, "bar", out.Foo)
+	assert.Equal(t, "baz", out.Bar)
+}
+
+func TestToTypedStructOverwrite(t *testing.T) {
+	type Tmp struct {
+		Foo string `json:"foo"`
+		Bar string `json:"bar,omitempty"`
+
+		// Baz must be skipped.
+		Baz string `json:""`
+
+		// Qux must be skipped.
+		Qux string `json:"-"`
+	}
+
+	var out = Tmp{
+		Foo: "baz",
+		Bar: "qux",
+	}
+	v := config.V(map[string]config.Value{
+		"foo": config.V("bar"),
+		"bar": config.V("baz"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Equal(t, "bar", out.Foo)
+	assert.Equal(t, "baz", out.Bar)
+}
+
+func TestToTypedStructAnonymousByValue(t *testing.T) {
+	type Bar struct {
+		Bar string `json:"bar"`
+	}
+
+	type Foo struct {
+		Foo string `json:"foo"`
+		Bar
+	}
+
+	type Tmp struct {
+		Foo
+	}
+
+	var out Tmp
+	v := config.V(map[string]config.Value{
+		"foo": config.V("bar"),
+		"bar": config.V("baz"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Equal(t, "bar", out.Foo.Foo)
+	assert.Equal(t, "baz", out.Foo.Bar.Bar)
+}
+
+func TestToTypedStructAnonymousByPointer(t *testing.T) {
+	type Bar struct {
+		Bar string `json:"bar"`
+	}
+
+	type Foo struct {
+		Foo string `json:"foo"`
+		*Bar
+	}
+
+	type Tmp struct {
+		*Foo
+	}
+
+	var out Tmp
+	v := config.V(map[string]config.Value{
+		"foo": config.V("bar"),
+		"bar": config.V("baz"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Equal(t, "bar", out.Foo.Foo)
+	assert.Equal(t, "baz", out.Foo.Bar.Bar)
+}
+
+func TestToTypedStructNil(t *testing.T) {
+	type Tmp struct {
+		Foo string `json:"foo"`
+	}
+
+	var out = Tmp{}
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Equal(t, Tmp{}, out)
+}
+
+func TestToTypedStructNilOverwrite(t *testing.T) {
+	type Tmp struct {
+		Foo string `json:"foo"`
+	}
+
+	var out = Tmp{"bar"}
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Equal(t, Tmp{}, out)
+}
+
+func TestToTypedMap(t *testing.T) {
+	var out = map[string]string{}
+
+	v := config.V(map[string]config.Value{
+		"key": config.V("value"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 1)
+	assert.Equal(t, "value", out["key"])
+}
+
+func TestToTypedMapOverwrite(t *testing.T) {
+	var out = map[string]string{
+		"foo": "bar",
+	}
+
+	v := config.V(map[string]config.Value{
+		"bar": config.V("qux"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 1)
+	assert.Equal(t, "qux", out["bar"])
+}
+
+func TestToTypedMapWithPointerElement(t *testing.T) {
+	var out map[string]*string
+
+	v := config.V(map[string]config.Value{
+		"key": config.V("value"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 1)
+	assert.Equal(t, "value", *out["key"])
+}
+
+func TestToTypedMapNil(t *testing.T) {
+	var out = map[string]string{}
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Nil(t, out)
+}
+
+func TestToTypedMapNilOverwrite(t *testing.T) {
+	var out = map[string]string{
+		"foo": "bar",
+	}
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Nil(t, out)
+}
+
+func TestToTypedSlice(t *testing.T) {
+	var out []string
+
+	v := config.V([]config.Value{
+		config.V("foo"),
+		config.V("bar"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 2)
+	assert.Equal(t, "foo", out[0])
+	assert.Equal(t, "bar", out[1])
+}
+
+func TestToTypedSliceOverwrite(t *testing.T) {
+	var out = []string{"qux"}
+
+	v := config.V([]config.Value{
+		config.V("foo"),
+		config.V("bar"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 2)
+	assert.Equal(t, "foo", out[0])
+	assert.Equal(t, "bar", out[1])
+}
+
+func TestToTypedSliceWithPointerElement(t *testing.T) {
+	var out []*string
+
+	v := config.V([]config.Value{
+		config.V("foo"),
+		config.V("bar"),
+	})
+
+	err := ToTyped(&out, v)
+	require.NoError(t, err)
+	assert.Len(t, out, 2)
+	assert.Equal(t, "foo", *out[0])
+	assert.Equal(t, "bar", *out[1])
+}
+
+func TestToTypedSliceNil(t *testing.T) {
+	var out []string
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Nil(t, out)
+}
+
+func TestToTypedSliceNilOverwrite(t *testing.T) {
+	var out = []string{"foo"}
+	err := ToTyped(&out, config.NilValue)
+	require.NoError(t, err)
+	assert.Nil(t, out)
+}
+
+func TestToTypedString(t *testing.T) {
+	var out string
+	err := ToTyped(&out, config.V("foo"))
+	require.NoError(t, err)
+	assert.Equal(t, "foo", out)
+}
+
+func TestToTypedStringOverwrite(t *testing.T) {
+	var out string = "bar"
+	err := ToTyped(&out, config.V("foo"))
+	require.NoError(t, err)
+	assert.Equal(t, "foo", out)
+}
+
+func TestToTypedStringFromBool(t *testing.T) {
+	var out string
+	err := ToTyped(&out, config.V(true))
+	require.NoError(t, err)
+	assert.Equal(t, "true", out)
+}
+
+func TestToTypedStringFromInt(t *testing.T) {
+	var out string
+	err := ToTyped(&out, config.V(123))
+	require.NoError(t, err)
+	assert.Equal(t, "123", out)
+}
+
+func TestToTypedStringFromFloat(t *testing.T) {
+	var out string
+	err := ToTyped(&out, config.V(1.2))
+	require.NoError(t, err)
+	assert.Equal(t, "1.2", out)
+}
+
+func TestToTypedBool(t *testing.T) {
+	var out bool
+	err := ToTyped(&out, config.V(true))
+	require.NoError(t, err)
+	assert.Equal(t, true, out)
+}
+
+func TestToTypedBoolOverwrite(t *testing.T) {
+	var out bool = true
+	err := ToTyped(&out, config.V(false))
+	require.NoError(t, err)
+	assert.Equal(t, false, out)
+}
+
+func TestToTypedBoolFromString(t *testing.T) {
+	var out bool
+
+	// True-ish
+	for _, v := range []string{"y", "yes", "on"} {
+		err := ToTyped(&out, config.V(v))
+		require.NoError(t, err)
+		assert.Equal(t, true, out)
+	}
+
+	// False-ish
+	for _, v := range []string{"n", "no", "off"} {
+		err := ToTyped(&out, config.V(v))
+		require.NoError(t, err)
+		assert.Equal(t, false, out)
+	}
+
+	// Other
+	err := ToTyped(&out, config.V("${var.foo}"))
+	require.Error(t, err)
+}
+
+func TestToTypedInt(t *testing.T) {
+	var out int
+	err := ToTyped(&out, config.V(1234))
+	require.NoError(t, err)
+	assert.Equal(t, int(1234), out)
+}
+
+func TestToTypedInt32(t *testing.T) {
+	var out32 int32
+	err := ToTyped(&out32, config.V(1235))
+	require.NoError(t, err)
+	assert.Equal(t, int32(1235), out32)
+}
+
+func TestToTypedInt64(t *testing.T) {
+	var out64 int64
+	err := ToTyped(&out64, config.V(1236))
+	require.NoError(t, err)
+	assert.Equal(t, int64(1236), out64)
+}
+
+func TestToTypedIntOverwrite(t *testing.T) {
+	var out int = 123
+	err := ToTyped(&out, config.V(1234))
+	require.NoError(t, err)
+	assert.Equal(t, int(1234), out)
+}
+
+func TestToTypedInt32Overwrite(t *testing.T) {
+	var out32 int32 = 123
+	err := ToTyped(&out32, config.V(1234))
+	require.NoError(t, err)
+	assert.Equal(t, int32(1234), out32)
+}
+
+func TestToTypedInt64Overwrite(t *testing.T) {
+	var out64 int64 = 123
+	err := ToTyped(&out64, config.V(1234))
+	require.NoError(t, err)
+	assert.Equal(t, int64(1234), out64)
+}
+
+func TestToTypedIntFromStringError(t *testing.T) {
+	var out int
+	err := ToTyped(&out, config.V("abc"))
+	require.Error(t, err)
+}
+
+func TestToTypedIntFromStringInt(t *testing.T) {
+	var out int
+	err := ToTyped(&out, config.V("123"))
+	require.NoError(t, err)
+	assert.Equal(t, int(123), out)
+}
+
+func TestToTypedFloat32(t *testing.T) {
+	var out float32
+	err := ToTyped(&out, config.V(float32(1.0)))
+	require.NoError(t, err)
+	assert.Equal(t, float32(1.0), out)
+}
+
+func TestToTypedFloat64(t *testing.T) {
+	var out float64
+	err := ToTyped(&out, config.V(float64(1.0)))
+	require.NoError(t, err)
+	assert.Equal(t, float64(1.0), out)
+}
+
+func TestToTypedFloat32Overwrite(t *testing.T) {
+	var out float32 = 1.0
+	err := ToTyped(&out, config.V(float32(2.0)))
+	require.NoError(t, err)
+	assert.Equal(t, float32(2.0), out)
+}
+
+func TestToTypedFloat64Overwrite(t *testing.T) {
+	var out float64 = 1.0
+	err := ToTyped(&out, config.V(float64(2.0)))
+	require.NoError(t, err)
+	assert.Equal(t, float64(2.0), out)
+}
+
+func TestToTypedFloat32FromStringError(t *testing.T) {
+	var out float32
+	err := ToTyped(&out, config.V("abc"))
+	require.Error(t, err)
+}
+
+func TestToTypedFloat64FromStringError(t *testing.T) {
+	var out float64
+	err := ToTyped(&out, config.V("abc"))
+	require.Error(t, err)
+}
+
+func TestToTypedFloat32FromString(t *testing.T) {
+	var out float32
+	err := ToTyped(&out, config.V("1.2"))
+	require.NoError(t, err)
+	assert.Equal(t, float32(1.2), out)
+}
+
+func TestToTypedFloat64FromString(t *testing.T) {
+	var out float64
+	err := ToTyped(&out, config.V("1.2"))
+	require.NoError(t, err)
+	assert.Equal(t, float64(1.2), out)
+}

libs/config/kind.go

@@ -0,0 +1,64 @@
+package config
+
+import "time"
+
+type Kind int
+
+const (
+	// Invalid is the zero value of Kind.
+	KindInvalid Kind = iota
+	KindMap
+	KindSequence
+	KindNil
+	KindString
+	KindBool
+	KindInt
+	KindFloat
+	KindTime
+)
+
+func kindOf(v any) Kind {
+	switch v.(type) {
+	case map[string]Value:
+		return KindMap
+	case []Value:
+		return KindSequence
+	case nil:
+		return KindNil
+	case string:
+		return KindString
+	case bool:
+		return KindBool
+	case int, int32, int64:
+		return KindInt
+	case float32, float64:
+		return KindFloat
+	case time.Time:
+		return KindTime
+	default:
+		panic("not handled")
+	}
+}
+
+func (k Kind) String() string {
+	switch k {
+	case KindMap:
+		return "map"
+	case KindSequence:
+		return "sequence"
+	case KindNil:
+		return "nil"
+	case KindString:
+		return "string"
+	case KindBool:
+		return "bool"
+	case KindInt:
+		return "int"
+	case KindFloat:
+		return "float"
+	case KindTime:
+		return "time"
+	default:
+		return "invalid"
+	}
+}

libs/config/value.go

@@ -1,9 +1,14 @@
 package config
 
-import "time"
+import (
+	"fmt"
+	"time"
+)
 
 type Value struct {
 	v any
+
+	k Kind
 	l Location
 
 	// Whether or not this value is an anchor.
@@ -12,12 +17,23 @@ type Value struct {
 }
 
 // NilValue is equal to the zero-value of Value.
-var NilValue = Value{}
+var NilValue = Value{
+	k: KindNil,
+}
+
+// V constructs a new Value with the given value.
+func V(v any) Value {
+	return Value{
+		v: v,
+		k: kindOf(v),
+	}
+}
 
 // NewValue constructs a new Value with the given value and location.
 func NewValue(v any, loc Location) Value {
 	return Value{
 		v: v,
+		k: kindOf(v),
 		l: loc,
 	}
 }
@@ -27,45 +43,47 @@ func (v Value) AsMap() (map[string]Value, bool) {
 	return m, ok
 }
 
+func (v Value) Kind() Kind {
+	return v.k
+}
+
 func (v Value) Location() Location {
 	return v.l
 }
 
 func (v Value) AsAny() any {
-	switch vv := v.v.(type) {
-	case map[string]Value:
-		m := make(map[string]any)
+	switch v.k {
+	case KindInvalid:
+		panic("invoked AsAny on invalid value")
+	case KindMap:
+		vv := v.v.(map[string]Value)
+		m := make(map[string]any, len(vv))
 		for k, v := range vv {
 			m[k] = v.AsAny()
 		}
 		return m
-	case []Value:
+	case KindSequence:
+		vv := v.v.([]Value)
 		a := make([]any, len(vv))
 		for i, v := range vv {
 			a[i] = v.AsAny()
 		}
 		return a
-	case string:
-		return vv
-	case bool:
-		return vv
-	case int:
-		return vv
-	case int32:
-		return vv
-	case int64:
-		return vv
-	case float32:
-		return vv
-	case float64:
-		return vv
-	case time.Time:
-		return vv
-	case nil:
-		return nil
+	case KindNil:
+		return v.v
+	case KindString:
+		return v.v
+	case KindBool:
+		return v.v
+	case KindInt:
+		return v.v
+	case KindFloat:
+		return v.v
+	case KindTime:
+		return v.v
 	default:
 		// Panic because we only want to deal with known types.
-		panic("not handled")
+		panic(fmt.Sprintf("invalid kind: %d", v.k))
 	}
 }
 
@@ -99,6 +117,7 @@ func (v Value) Index(i int) Value {
 func (v Value) MarkAnchor() Value {
 	return Value{
 		v: v.v,
+		k: v.k,
 		l: v.l,
 
 		anchor: true,
@@ -108,3 +127,47 @@ func (v Value) MarkAnchor() Value {
 func (v Value) IsAnchor() bool {
 	return v.anchor
 }
+
+func (v Value) MustMap() map[string]Value {
+	return v.v.(map[string]Value)
+}
+
+func (v Value) MustSequence() []Value {
+	return v.v.([]Value)
+}
+
+func (v Value) MustString() string {
+	return v.v.(string)
+}
+
+func (v Value) MustBool() bool {
+	return v.v.(bool)
+}
+
+func (v Value) MustInt() int64 {
+	switch vv := v.v.(type) {
+	case int:
+		return int64(vv)
+	case int32:
+		return int64(vv)
+	case int64:
+		return int64(vv)
+	default:
+		panic("not an int")
+	}
+}
+
+func (v Value) MustFloat() float64 {
+	switch vv := v.v.(type) {
+	case float32:
+		return float64(vv)
+	case float64:
+		return float64(vv)
+	default:
+		panic("not a float")
+	}
+}
+
+func (v Value) MustTime() time.Time {
+	return v.v.(time.Time)
+}