From 753390a8b6eeb3f129f28e566f558c2fac3240f3 Mon Sep 17 00:00:00 2001
From: Thomas Gossmann <gossi@users.noreply.github.com>
Date: Thu, 17 Aug 2023 21:42:45 +0200
Subject: [PATCH 1/2] Allow generics in Signatures

---
 packages/template/-private/signature.d.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/template/-private/signature.d.ts b/packages/template/-private/signature.d.ts
index 7d525fe24..dbea75e7e 100644
--- a/packages/template/-private/signature.d.ts
+++ b/packages/template/-private/signature.d.ts
@@ -45,7 +45,7 @@ export type ComponentSignatureBlocks<S> = S extends { Blocks: infer Blocks }
 
 /** Given a component signature `S`, get back the `Element` type. */
 export type ComponentSignatureElement<S> = S extends { Element: infer Element }
-  ? NonNullable<Element> extends never
+  ? Element extends null
     ? unknown
     : Element
   : unknown;

From f79c9c5160c6c0563920def28ee8a6fe75a3f9b0 Mon Sep 17 00:00:00 2001
From: gossi <gossi@users.noreply.github.com>
Date: Sat, 9 Sep 2023 17:40:29 +0200
Subject: [PATCH 2/2] attempt to add failing type tests

---
 packages/template/-private/signature.d.ts     |  3 +-
 packages/template/__tests__/signature.test.ts | 54 +++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/packages/template/-private/signature.d.ts b/packages/template/-private/signature.d.ts
index dbea75e7e..00baf4481 100644
--- a/packages/template/-private/signature.d.ts
+++ b/packages/template/-private/signature.d.ts
@@ -45,7 +45,8 @@ export type ComponentSignatureBlocks<S> = S extends { Blocks: infer Blocks }
 
 /** Given a component signature `S`, get back the `Element` type. */
 export type ComponentSignatureElement<S> = S extends { Element: infer Element }
-  ? Element extends null
+  ? NonNullable<Element> extends never 
+// ? Element extends null
     ? unknown
     : Element
   : unknown;
diff --git a/packages/template/__tests__/signature.test.ts b/packages/template/__tests__/signature.test.ts
index fa59161d1..d696a3f44 100644
--- a/packages/template/__tests__/signature.test.ts
+++ b/packages/template/__tests__/signature.test.ts
@@ -4,6 +4,7 @@ import {
   ComponentSignatureBlocks,
   ComponentSignatureElement,
 } from '../-private/signature';
+import { ComponentLike } from '../';
 
 type LegacyArgs = {
   foo: number;
@@ -153,3 +154,56 @@ interface FullLongSig {
 expectTypeOf<ComponentSignatureArgs<FullLongSig>>().toEqualTypeOf<FullLongSig['Args']>();
 expectTypeOf<ComponentSignatureBlocks<FullLongSig>>().toEqualTypeOf<FullLongSig['Blocks']>();
 expectTypeOf<ComponentSignatureElement<FullLongSig>>().toEqualTypeOf<FullLongSig['Element']>();
+
+// types to simulate the `(element)` helper
+// Issue: https://github.com/typed-ember/glint/issues/610
+type ElementFromTagName<T extends string> = T extends keyof HTMLElementTagNameMap
+  ? HTMLElementTagNameMap[T]
+  : Element;
+type ElementHelperPositional<T extends string> = [name: T];
+type ElementHelperReturn<T extends string> = ComponentLike<{
+  Element: ElementFromTagName<T>;
+  Blocks: { default: [] };
+}>;
+
+interface ElementSignature<T extends string> {
+  Args: {
+    Positional: ElementHelperPositional<T>;
+  };
+  Return: ElementHelperReturn<T> | undefined;
+}
+
+// signature for a component receiving an `(element)`
+interface ElementReceiverSignature<T extends string> {
+  Element: ElementFromTagName<T>;
+  Args: {
+    element: ElementSignature<T>['Return'];
+  };
+  Blocks: {
+    default: [];
+  };
+}
+
+expectTypeOf<ComponentSignatureArgs<ElementReceiverSignature<'div'>>>().toEqualTypeOf<{
+  Named: {
+    element: ElementSignature<'div'>['Return'];
+  };
+  Positional: []
+}>();
+
+expectTypeOf<ComponentSignatureArgs<ElementReceiverSignature<null>>>().toEqualTypeOf<{
+  Named: {
+    element: {
+      Args: {
+        Positional: ElementHelperPositional<never>;
+      };
+      Return: ComponentLike<{
+        Element: Element;
+        Blocks: { default: [] };
+      }> | undefined;
+    } | undefined;
+  };
+  Positional: []
+}>();
+expectTypeOf<ComponentSignatureElement<ElementReceiverSignature<'div'>>>().toEqualTypeOf<HTMLDivElement>();
+