From a9b21cd70827058ae9ce90a459d303b27b34e420 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Mendelski?= <mendelski.pawel@gmail.com>
Date: Sat, 4 Mar 2023 12:52:37 +0100
Subject: [PATCH] Fix nil error value returned from a provider

---
 Makefile                     |  2 +-
 holder.go                    | 13 +++++++++----
 test/lazy_dependency_test.go |  5 +++++
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index cf882c4..d95489f 100644
--- a/Makefile
+++ b/Makefile
@@ -102,7 +102,7 @@ format: ## Format source files
 .PHONY: outdated
 outdated: ## Print outdated dependencies
 	@go mod tidy
-	@go list -u -m -json all | $(GOMODOUDATED_CMD) -update -direct
+	@go list -u -m -json all | $(GOMODOUTDATED_CMD) -update -direct
 
 .PHONY: weight
 weight: ## Print info about package weight
diff --git a/holder.go b/holder.go
index b00045a..beed496 100644
--- a/holder.go
+++ b/holder.go
@@ -39,9 +39,11 @@ func createLazyHolder(ctor any) (*holder, *Error) {
 	if ctype.IsVariadic() {
 		return nil, newInvalidConstructorError("variadic parameters not supported (use slice instead)")
 	}
-	errorInterface := reflect.TypeOf((*error)(nil)).Elem()
-	if numResults == 2 && !ctype.Out(1).AssignableTo(errorInterface) {
-		return nil, newInvalidConstructorError("expected second result value to be an error")
+	if numResults == 2 {
+		outtype := reflect.New(ctype.Out(1))
+		if _, ok := outtype.Interface().(*error); !ok {
+			return nil, newInvalidConstructorError("expected second result value to be an error")
+		}
 	}
 	resultType := ctype.Out(0)
 	numArgs := ctype.NumIn()
@@ -75,9 +77,12 @@ func createLazyHolder(ctor any) (*holder, *Error) {
 		result := cval.Call(args)
 		obj := result[0].Interface()
 		if len(result) == 2 {
+			if result[1].IsNil() {
+				return obj, nil
+			}
 			err, ok := result[1].Interface().(error)
 			if !ok {
-				return nil, newInvalidConstructorError("expected second result value to be an error")
+				return nil, newInvalidConstructorError("expected second result value to be an error xxxx")
 			}
 			return obj, err
 		}
diff --git a/test/lazy_dependency_test.go b/test/lazy_dependency_test.go
index 7fa9ddb..aedf74a 100644
--- a/test/lazy_dependency_test.go
+++ b/test/lazy_dependency_test.go
@@ -25,6 +25,11 @@ func (suite *LazyDependencySuite) TestGetByType() {
 			provide: func(ctxb *di.ContextBuilder) { ctxb.Provide(func() *Foo { return &foo }) },
 			get:     func(ctx *di.Context) (any, error) { return di.GetOrErr[*Foo](ctx) },
 		},
+		{
+			value:   &foo,
+			provide: func(ctxb *di.ContextBuilder) { ctxb.Provide(func() (*Foo, error) { return &foo, nil }) },
+			get:     func(ctx *di.Context) (any, error) { return di.GetOrErr[*Foo](ctx) },
+		},
 		{
 			value:   foo,
 			provide: func(ctxb *di.ContextBuilder) { ctxb.Provide(func() Foo { return foo }) },