From 3a0fba4bdbc326153d4f5a9241c1afad6bb898f7 Mon Sep 17 00:00:00 2001
From: Masaaki Goshima <goccy54@gmail.com>
Date: Wed, 24 Mar 2021 19:09:33 +0900
Subject: [PATCH] Fix invalid string option

---
 decode_compile.go | 24 +++++++++++++++++++++++-
 decode_test.go    |  3 ---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/decode_compile.go b/decode_compile.go
index 67b2f0b..62f3a61 100644
--- a/decode_compile.go
+++ b/decode_compile.go
@@ -102,6 +102,28 @@ func decodeCompile(typ *rtype, structName, fieldName string, structTypeToDecoder
 	}
 }
 
+func isStringTagSupportedType(typ *rtype) bool {
+	switch {
+	case rtype_ptrTo(typ).Implements(unmarshalJSONType):
+		return false
+	case rtype_ptrTo(typ).Implements(unmarshalTextType):
+		return false
+	}
+	switch typ.Kind() {
+	case reflect.Map:
+		return false
+	case reflect.Slice:
+		return false
+	case reflect.Array:
+		return false
+	case reflect.Struct:
+		return false
+	case reflect.Interface:
+		return false
+	}
+	return true
+}
+
 func decodeCompileMapKey(typ *rtype, structName, fieldName string, structTypeToDecoder map[uintptr]decoder) (decoder, error) {
 	if rtype_ptrTo(typ).Implements(unmarshalTextType) {
 		return newUnmarshalTextDecoder(rtype_ptrTo(typ), structName, fieldName), nil
@@ -416,7 +438,7 @@ func decodeCompileStruct(typ *rtype, structName, fieldName string, structTypeToD
 				}
 			}
 		} else {
-			if tag.IsString {
+			if tag.IsString && isStringTagSupportedType(type2rtype(field.Type)) {
 				dec = newWrappedStringDecoder(type2rtype(field.Type), dec, structName, field.Name)
 			}
 			var key string
diff --git a/decode_test.go b/decode_test.go
index 7d933c2..ab4b9eb 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -2514,7 +2514,6 @@ func TestInvalidUnmarshalText(t *testing.T) {
 	}
 }
 
-/*
 // Test that string option is ignored for invalid types.
 // Issue 9812.
 func TestInvalidStringOption(t *testing.T) {
@@ -2532,13 +2531,11 @@ func TestInvalidStringOption(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Marshal: %v", err)
 	}
-
 	err = json.Unmarshal(data, &item)
 	if err != nil {
 		t.Fatalf("Unmarshal: %v", err)
 	}
 }
-*/
 
 // Test unmarshal behavior with regards to embedded unexported structs.
 //