From 1ba8cc87296eb180b74a9c3b24d27e3b2eba9d57 Mon Sep 17 00:00:00 2001
From: Marco Munizaga <git@marcopolo.io>
Date: Tue, 26 Aug 2025 12:09:43 -0700
Subject: [PATCH] rename interface types and add isSet

---
 di.go | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/di.go b/di.go
index 83caa311de10b5c2a06740fd4382520f9de94dee..00660c60599fab8424fb75dfe8a6b9de1f4fcf78 100644
--- a/di.go
+++ b/di.go
@@ -37,6 +37,7 @@ import (
 
 type Provide[Out any] struct {
 	fOrV any
+	set  bool
 }
 
 // Optional is the canonical way of specifying a field is optional. The library
@@ -60,12 +61,14 @@ func Some[T any](val T) Optional[T] {
 }
 
 type provideI interface {
-	diOutType() reflect.Type
-	diPayload() any
+	outT() reflect.Type
+	payload() any
+	isSet() bool
 }
 
-func (p Provide[Out]) diOutType() reflect.Type { return typeOf[Out]() }
-func (p Provide[Out]) diPayload() any          { return p.fOrV }
+func (p Provide[Out]) outT() reflect.Type { return typeOf[Out]() }
+func (p Provide[Out]) payload() any       { return p.fOrV }
+func (p Provide[Out]) isSet() bool        { return p.set }
 
 // SideEffect is a canonical value representing a constructor used only for side
 // effects such as introducing two components together without a circular
@@ -292,8 +295,11 @@ func (c *collector) collect(v reflect.Value, path string) error {
 
 		// Provide[T] (singular) must be recognized BEFORE treating structs as namespaces.
 		if pi, ok := asProvide(fv); ok {
-			outT := pi.diOutType()
-			payload := pi.diPayload()
+			outT := pi.outT()
+			payload := pi.payload()
+			if !pi.isSet() {
+				return fmt.Errorf("Missing Provide[%s]", outT)
+			}
 			if payload == nil {
 				c.values[outT] = reflect.Zero(outT)
 				continue
@@ -326,15 +332,15 @@ func (c *collector) collect(v reflect.Value, path string) error {
 			if provideElem, ok := reflect.New(fv.Type().Elem()).Elem().Interface().(provideI); ok {
 				if fv.Len() == 0 && !fv.IsNil() {
 					// Set presence of empty list
-					outT := provideElem.diOutType()
+					outT := provideElem.outT()
 					c.listPresence[outT] = true
 				}
 
 				for j := 0; j < fv.Len(); j++ {
 					pi := fv.Index(j).Interface().(provideI)
-					outT := pi.diOutType()
+					outT := pi.outT()
 					c.listPresence[outT] = true
-					payload := pi.diPayload()
+					payload := pi.payload()
 					if payload == nil {
 						c.listValues[outT] = append(c.listValues[outT], reflect.Zero(outT))
 						continue