From 5b5f6e32a8fa90b185daf7f30aeed01157a26656 Mon Sep 17 00:00:00 2001
From: Tom <73077675+tmzane@users.noreply.github.com>
Date: Wed, 8 May 2024 17:22:35 +0300
Subject: [PATCH] fix: check whether a pointer-type implements a Marshaler
 interface (#94)

---
 musttag.go                  |  2 +-
 testdata/src/tests/tests.go | 28 +++++++++++-----------------
 2 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/musttag.go b/musttag.go
index 7be684f..70c8420 100644
--- a/musttag.go
+++ b/musttag.go
@@ -273,7 +273,7 @@ func implementsInterface(typ types.Type, ifaces []string, imports []*types.Packa
 		if !ok {
 			continue
 		}
-		if types.Implements(typ, iface) {
+		if types.Implements(typ, iface) || types.Implements(types.NewPointer(typ), iface) {
 			return true
 		}
 	}
diff --git a/testdata/src/tests/tests.go b/testdata/src/tests/tests.go
index 25461a1..0d4e766 100644
--- a/testdata/src/tests/tests.go
+++ b/testdata/src/tests/tests.go
@@ -131,23 +131,17 @@ func shouldBeIgnored() {
 	json.Marshal(nil) // nil argument, see issue #20.
 }
 
-type WithInterface struct {
-	NoTag string
-}
-
-func (w WithInterface) MarshalJSON() ([]byte, error) {
-	return json.Marshal(w.NoTag)
-}
-
 func nestedTypeWithInterface() {
 	type Foo struct {
-		Nested WithInterface `json:"nested"`
+		Nested Marshaler `json:"nested"`
 	}
 	var foo Foo
-	json.Marshal(foo)    // no error
-	json.Marshal(&foo)   // no error
-	json.Marshal(Foo{})  // no error
-	json.Marshal(&Foo{}) // no error
+	json.Marshal(foo)
+	json.Marshal(&foo)
+	json.Marshal(Foo{})
+	json.Marshal(&Foo{})
+	json.Unmarshal(nil, &foo)
+	json.Unmarshal(nil, &Foo{})
 }
 
 func ignoredNestedType() {
@@ -159,10 +153,10 @@ func ignoredNestedType() {
 		Exported string `json:"exported"`
 	}
 	var foo Foo
-	json.Marshal(foo)    // no error
-	json.Marshal(&foo)   // no error
-	json.Marshal(Foo{})  // no error
-	json.Marshal(&Foo{}) // no error
+	json.Marshal(foo)
+	json.Marshal(&foo)
+	json.Marshal(Foo{})
+	json.Marshal(&Foo{})
 }
 
 func ignoredNestedTypeWithSubsequentNoTagField() {