From 01f11fbbcd7483bad79f1320ffa80cb7818aa573 Mon Sep 17 00:00:00 2001
From: Nuruddin Ashr <uudashr@gmail.com>
Date: Wed, 8 Jan 2025 10:05:19 +0700
Subject: [PATCH] Handle untyped nil

---
 opaque/opaque.go                  | 15 +++++++++++++--
 opaque/testdata/src/a/a.go        |  9 +++++++++
 opaque/testdata/src/a/a.go.golden |  9 +++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/opaque/opaque.go b/opaque/opaque.go
index 59e4063..500249d 100644
--- a/opaque/opaque.go
+++ b/opaque/opaque.go
@@ -157,12 +157,15 @@ func (r *runner) run(pass *analysis.Pass) (interface{}, error) {
 						}
 
 						typ := pass.TypesInfo.TypeOf(res)
+						isNilStmt := isUntypedNil(typ)
 
 						if r.debug {
-							fmt.Printf("        Ident type: %v %v interface=%t\n", typ, reflect.TypeOf(typ), types.IsInterface(typ))
+							fmt.Printf("        Ident type: %v %v interface=%t, untypedNil=%t\n", typ, reflect.TypeOf(typ), types.IsInterface(typ), isNilStmt)
 						}
 
-						retStmtTypes[i][typ] = struct{}{}
+						if !isNilStmt {
+							retStmtTypes[i][typ] = struct{}{}
+						}
 					case *ast.UnaryExpr:
 						if r.debug {
 							fmt.Printf("       UnaryExpr X: %v \n", res.X)
@@ -302,6 +305,14 @@ func (r *runner) run(pass *analysis.Pass) (interface{}, error) {
 	return nil, nil
 }
 
+func isUntypedNil(typ types.Type) bool {
+	if b, ok := typ.(*types.Basic); ok {
+		return b.Kind() == types.UntypedNil
+	}
+
+	return false
+}
+
 func positionStr(idx int) string {
 	switch idx {
 	case 0:
diff --git a/opaque/testdata/src/a/a.go b/opaque/testdata/src/a/a.go
index 8180f12..52cb352 100644
--- a/opaque/testdata/src/a/a.go
+++ b/opaque/testdata/src/a/a.go
@@ -1,5 +1,7 @@
 package app
 
+import "errors"
+
 type Server interface {
 	Serve() error
 }
@@ -24,6 +26,13 @@ func NewServer3(addr string) Server { // want "NewServer3 function return Server
 	return &server{addr: addr}
 }
 
+func NewServer4(addr string) (Server, error) { // want "NewServer4 function return Server interface at the 1st result, abstract a single concrete implementation of \\*server"
+	if addr == "" {
+		return nil, errors.New("addr cannot be nil")
+	}
+	return &server{addr: addr}, nil
+}
+
 func newServer(addr string) *server {
 	return &server{addr: addr}
 }
diff --git a/opaque/testdata/src/a/a.go.golden b/opaque/testdata/src/a/a.go.golden
index 92949db..532e99c 100644
--- a/opaque/testdata/src/a/a.go.golden
+++ b/opaque/testdata/src/a/a.go.golden
@@ -1,5 +1,7 @@
 package app
 
+import "errors"
+
 type Server interface {
 	Serve() error
 }
@@ -24,6 +26,13 @@ func NewServer3(addr string) *server { // want "NewServer3 function return Serve
 	return &server{addr: addr}
 }
 
+func NewServer4(addr string) (*server, error) { // want "NewServer4 function return Server interface at the 1st result, abstract a single concrete implementation of \\*server"
+	if addr == "" {
+		return nil, errors.New("addr cannot be nil")
+	}
+	return &server{addr: addr}, nil
+}
+
 func newServer(addr string) *server {
 	return &server{addr: addr}
 }