From a0950f4c29b0b72fc1df867dcfb4d4ad86ec3ca4 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Mon, 1 Aug 2022 21:55:34 -0600
Subject: wip

---
 lib/lowmemjson/decode.go | 50 +++++++++++++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/lib/lowmemjson/decode.go b/lib/lowmemjson/decode.go
index c2e7ab1..aeca291 100644
--- a/lib/lowmemjson/decode.go
+++ b/lib/lowmemjson/decode.go
@@ -108,7 +108,6 @@ func _Decode(r io.RuneScanner, ptr any, cfg decodeConfig) (err error) {
 
 var (
 	rawMessagePtrType   = reflect.TypeOf((*json.RawMessage)(nil))
-	anyType             = reflect.TypeOf((*any)(nil)).Elem()
 	decoderType         = reflect.TypeOf((*Decoder)(nil)).Elem()
 	jsonUnmarshalerType = reflect.TypeOf((*json.Unmarshaler)(nil)).Elem()
 	textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
@@ -200,16 +199,27 @@ func decode(r io.RuneScanner, val reflect.Value, cfg decodeConfig) {
 				val.SetString(buf.String())
 			}
 		case reflect.Interface:
-			if val.IsNil() {
-				if typ == anyType {
-					val.Set(reflect.ValueOf(decodeAny(r, cfg)))
+			if typ.NumMethod() > 0 {
+				panic(decodeError{&json.UnsupportedTypeError{
+					Type: typ,
+				}})
+			}
+			switch peekRune(r) {
+			case 'n':
+				if !val.IsNil() && val.Elem().Kind() == reflect.Pointer && val.Elem().Elem().Kind() == reflect.Pointer {
+					// XXX: I can't justify this case, other than "it's what encoding/json does, but
+					// I don't understand their rationale".
+					decode(r, val.Elem(), cfg)
 				} else {
-					panic(decodeError{&json.UnsupportedTypeError{
-						Type: typ,
-					}})
+					decodeNull(r)
+					val.Set(reflect.Zero(typ))
+				}
+			default:
+				if !val.IsNil() && val.Elem().Kind() == reflect.Pointer {
+					decode(r, val.Elem(), cfg)
+				} else {
+					val.Set(reflect.ValueOf(decodeAny(r, cfg)))
 				}
-			} else {
-				decode(r, val.Elem(), cfg)
 			}
 		case reflect.Struct:
 			index := indexStruct(typ)
@@ -244,8 +254,8 @@ func decode(r io.RuneScanner, val reflect.Value, cfg decodeConfig) {
 					case 'n':
 						decodeNull(r)
 						switch fVal.Kind() {
-						// I can't justify this list, other than that it's what encoding/json
-						// does.  I don't understand their rationale.
+						// XXX: I can't justify this list, other than "it's what encoding/json
+						// does, but I don't understand their rationale".
 						case reflect.Interface, reflect.Pointer, reflect.Map, reflect.Slice:
 							fVal.Set(reflect.Zero(fVal.Type()))
 						}
@@ -341,10 +351,20 @@ func decode(r io.RuneScanner, val reflect.Value, cfg decodeConfig) {
 				i++
 			})
 		case reflect.Pointer:
-			if val.IsNil() {
-				val.Set(reflect.New(typ.Elem()))
+			switch peekRune(r) {
+			case 'n':
+				decodeNull(r)
+				for val.IsNil() && typ.Elem().Kind() == reflect.Pointer {
+					val.Set(reflect.New(typ.Elem()))
+					val = val.Elem()
+				}
+				val.Elem().Set(reflect.Zero(val.Type().Elem()))
+			default:
+				if val.IsNil() {
+					val.Set(reflect.New(typ.Elem()))
+				}
+				decode(r, val.Elem(), cfg)
 			}
-			decode(r, val.Elem(), cfg)
 		default:
 			panic(decodeError{&json.UnsupportedTypeError{
 				Type: typ,
@@ -409,7 +429,7 @@ func scanNumber(r io.RuneScanner, out io.Writer) {
 	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
 		scan(r, out)
 	default:
-		panic(decodeError{fmt.Errorf("expected a nubmer but got %c", c)})
+		panic(decodeError{fmt.Errorf("expected a number but got %c", c)})
 	}
 }
 
-- 
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