Library to convert config.Value to Go struct

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"])
+}