Add a new conversion utility vals.ScanMapToGo.

pkg/eval/options.go

@@ -1,12 +1,10 @@
 package eval
 
 import (
-	"fmt"
 	"reflect"
 
 	"src.elv.sh/pkg/eval/vals"
 	"src.elv.sh/pkg/parse"
-	"src.elv.sh/pkg/strutil"
 )
 
 // UnknownOption is thrown by a native function when called with an unknown option.
@@ -28,31 +26,18 @@ type RawOptions map[string]interface{}
 // with options. A field named FieldName corresponds to the option named
 // field-name. Options that don't have corresponding fields in the struct causes
 // an error.
+//
+// Similar to vals.ScanMapToGo, but requires rawOpts to contain a subset of keys
+// supported by the struct.
 func scanOptions(rawOpts RawOptions, ptr interface{}) error {
-	ptrValue := reflect.ValueOf(ptr)
-	if ptrValue.Kind() != reflect.Ptr || ptrValue.Elem().Kind() != reflect.Struct {
-		return fmt.Errorf(
-			"internal bug: need struct ptr to scan options, got %T", ptr)
-	}
-
-	// fieldIdxForOpt maps option name to the index of field in `struc`.
-	fieldIdxForOpt := make(map[string]int)
-	struc := ptrValue.Elem()
-	for i := 0; i < struc.Type().NumField(); i++ {
-		if !struc.Field(i).CanSet() {
-			continue // ignore unexported fields
-		}
-		f := struc.Type().Field(i)
-		optName := strutil.CamelToDashed(f.Name)
-		fieldIdxForOpt[optName] = i
-	}
-
+	_, keyIdx := vals.StructFieldsInfo(reflect.TypeOf(ptr).Elem())
+	structValue := reflect.ValueOf(ptr).Elem()
 	for k, v := range rawOpts {
-		fieldIdx, ok := fieldIdxForOpt[k]
+		fieldIdx, ok := keyIdx[k]
 		if !ok {
 			return UnknownOption{k}
 		}
-		err := vals.ScanToGo(v, struc.Field(fieldIdx).Addr().Interface())
+		err := vals.ScanToGo(v, structValue.Field(fieldIdx).Addr().Interface())
 		if err != nil {
 			return err
 		}

pkg/eval/options_test.go

@@ -1,45 +1,30 @@
 package eval
 
 import (
+	"reflect"
 	"testing"
+
+	. "src.elv.sh/pkg/tt"
 )
 
 type opts struct {
-	FooBar string
-	Min    int
-	ignore bool // this should be ignored since it isn't exported
-}
-
-var scanOptionsTests = []struct {
-	rawOpts  RawOptions
-	preScan  opts
-	postScan opts
-	err      error
-}{
-	{RawOptions{"foo-bar": "lorem ipsum"},
-		opts{}, opts{FooBar: "lorem ipsum"}, nil},
-	// Since "ignore" is not exported it will result in an error when used.
-	{RawOptions{"ignore": true},
-		opts{}, opts{ignore: false}, UnknownOption{"ignore"}},
+	Foo string
+	bar int
 }
 
 func TestScanOptions(t *testing.T) {
-	// scanOptions requires a pointer to struct.
-	err := scanOptions(RawOptions{}, opts{})
-	if err == nil {
-		t.Errorf("Scan should have reported invalid options arg error")
+	// A wrapper of ScanOptions, to make it easier to test
+	wrapper := func(src RawOptions, dstInit interface{}) (interface{}, error) {
+		ptr := reflect.New(reflect.TypeOf(dstInit))
+		ptr.Elem().Set(reflect.ValueOf(dstInit))
+		err := scanOptions(src, ptr.Interface())
+		return ptr.Elem().Interface(), err
 	}
 
-	for _, test := range scanOptionsTests {
-		opts := test.preScan
-		err := scanOptions(test.rawOpts, &opts)
-
-		if ((err == nil) != (test.err == nil)) ||
-			(err != nil && test.err != nil && err.Error() != test.err.Error()) {
-			t.Errorf("Scan error mismatch %v: want %q, got %q", test.rawOpts, test.err, err)
-		}
-		if opts != test.postScan {
-			t.Errorf("Scan %v => %v, want %v", test.rawOpts, opts, test.postScan)
-		}
-	}
+	Test(t, Fn("scanOptions", wrapper), Table{
+		Args(RawOptions{"foo": "lorem ipsum"}, opts{}).
+			Rets(opts{Foo: "lorem ipsum"}, nil),
+		Args(RawOptions{"bar": 20}, opts{bar: 10}).
+			Rets(opts{bar: 10}, UnknownOption{"bar"}),
+	})
 }

pkg/eval/vals/conversion.go

@@ -6,9 +6,11 @@ import (
 	"math/big"
 	"reflect"
 	"strconv"
+	"sync"
 	"unicode/utf8"
 
 	"src.elv.sh/pkg/eval/errs"
+	"src.elv.sh/pkg/strutil"
 )
 
 // Conversion between "Go values" (those expected by native Go functions) and
@@ -215,6 +217,68 @@ func ScanListElementsToGo(src List, ptrs ...interface{}) error {
 	return nil
 }
 
+// ScanMapToGo scans map elements into ptr, which must be a pointer to a struct.
+// Struct field names are converted to map keys with CamelToDashed.
+//
+// The map may contains keys that don't correspond to struct fields, and it
+// doesn't have to contain all keys that correspond to struct fields.
+func ScanMapToGo(src Map, ptr interface{}) error {
+	// Iterate over the struct keys instead of the map: since extra keys are
+	// allowed, the map may be very big, while the size of the struct is bound.
+	keys, _ := StructFieldsInfo(reflect.TypeOf(ptr).Elem())
+	structValue := reflect.ValueOf(ptr).Elem()
+	for i, key := range keys {
+		if key == "" {
+			continue
+		}
+		val, ok := src.Index(key)
+		if !ok {
+			continue
+		}
+		err := ScanToGo(val, structValue.Field(i).Addr().Interface())
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// StructFieldsInfo takes a type for a struct, and returns a slice for each
+// field name, converted with CamelToDashed, and a reverse index. Unexported
+// fields result in an empty string in the slice, and is omitted from the
+// reverse index.
+func StructFieldsInfo(t reflect.Type) ([]string, map[string]int) {
+	if info, ok := structFieldsInfoCache.Load(t); ok {
+		info := info.(structFieldsInfo)
+		return info.keys, info.keyIdx
+	}
+	info := makeStructFieldsInfo(t)
+	structFieldsInfoCache.Store(t, info)
+	return info.keys, info.keyIdx
+}
+
+var structFieldsInfoCache sync.Map
+
+type structFieldsInfo struct {
+	keys   []string
+	keyIdx map[string]int
+}
+
+func makeStructFieldsInfo(t reflect.Type) structFieldsInfo {
+	keys := make([]string, t.NumField())
+	keyIdx := make(map[string]int)
+	for i := 0; i < t.NumField(); i++ {
+		field := t.Field(i)
+		if field.PkgPath != "" {
+			continue
+		}
+		key := strutil.CamelToDashed(field.Name)
+		keyIdx[key] = i
+		keys[i] = key
+	}
+	return structFieldsInfo{keys, keyIdx}
+}
+
 // FromGo converts a Go value to an Elvish value.
 //
 // Exact numbers are normalized to the smallest types that can hold them, and

pkg/eval/vals/conversion_test.go

@@ -159,6 +159,35 @@ func TestScanListElementsToGo(t *testing.T) {
 	})
 }
 
+type aStruct struct {
+	Foo int
+	bar interface{}
+}
+
+func TestScanMapToGo(t *testing.T) {
+	// A wrapper around ScanMapToGo, to make it easier to test.
+	scanMapToGo := func(src Map, dstInit interface{}) (interface{}, error) {
+		ptr := reflect.New(TypeOf(dstInit))
+		ptr.Elem().Set(reflect.ValueOf(dstInit))
+		err := ScanMapToGo(src, ptr.Interface())
+		return ptr.Elem().Interface(), err
+	}
+
+	Test(t, Fn("ScanListToGo", scanMapToGo), Table{
+		Args(MakeMap("foo", "1"), aStruct{}).Rets(aStruct{Foo: 1}),
+		// More fields is OK
+		Args(MakeMap("foo", "1", "bar", "x"), aStruct{}).Rets(aStruct{Foo: 1}),
+		// Fewer fields is OK
+		Args(MakeMap(), aStruct{}).Rets(aStruct{}),
+		// Unexported fields are ignored
+		Args(MakeMap("bar", 20), aStruct{bar: 10}).Rets(aStruct{bar: 10}),
+
+		// Conversion error
+		Args(MakeMap("foo", "a"), aStruct{}).
+			Rets(aStruct{}, cannotParseAs{"integer", "a"}),
+	})
+}
+
 func TestFromGo(t *testing.T) {
 	Test(t, Fn("FromGo", FromGo), Table{
 		// BigInt -> int, when in range