From da73d7f07631de814c5fc1d9de4605b74b7dfcb5 Mon Sep 17 00:00:00 2001
From: Ben Lovy <ben@deciduously.com>
Date: Tue, 19 Nov 2024 15:56:24 -0500
Subject: [PATCH 1/4] add test

---
 packages/server/src/package/check/tests.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/packages/server/src/package/check/tests.rs b/packages/server/src/package/check/tests.rs
index 10f46f434..a913c1283 100644
--- a/packages/server/src/package/check/tests.rs
+++ b/packages/server/src/package/check/tests.rs
@@ -70,6 +70,26 @@ async fn nonexistent_function() -> tg::Result<()> {
 	.await
 }
 
+#[tokio::test]
+async fn no_return_value() -> tg::Result<()> {
+	test(
+		temp::directory! {
+			"tangram.ts" => indoc!(r"
+				export default tg.target(() => {});
+			"),
+		},
+		|_, output| async move {
+			assert_json_snapshot!(output, @r#"
+   {
+     "diagnostics": []
+   }
+   "#);
+			Ok(())
+		},
+	)
+	.await
+}
+
 async fn test<F, Fut>(artifact: temp::Artifact, assertions: F) -> tg::Result<()>
 where
 	F: FnOnce(Server, tg::package::check::Output) -> Fut,

From 05697aa593aeac7298c5fc3dcca4d10488853ff5 Mon Sep 17 00:00:00 2001
From: David Yamnitsky <david@yamnitsky.com>
Date: Mon, 25 Nov 2024 15:51:18 -0500
Subject: [PATCH 2/4] impl

---
 biome.json                      |  1 +
 packages/runtime/src/resolve.ts |  6 ++++--
 packages/runtime/src/target.ts  | 14 +++++++-------
 packages/runtime/tangram.d.ts   | 14 ++++++++------
 4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/biome.json b/biome.json
index dadb42fa7..0dca84ebc 100644
--- a/biome.json
+++ b/biome.json
@@ -20,6 +20,7 @@
 				"useConst": "off"
 			},
 			"suspicious": {
+				"noConfusingVoidType": "off",
 				"noExplicitAny": "off",
 				"noRedeclare": "off",
 				"useIsArray": "off"
diff --git a/packages/runtime/src/resolve.ts b/packages/runtime/src/resolve.ts
index 542cd2646..47d31892c 100644
--- a/packages/runtime/src/resolve.ts
+++ b/packages/runtime/src/resolve.ts
@@ -2,8 +2,9 @@ import * as im from "immutable";
 import * as tg from "./index.ts";
 import type { MaybePromise } from "./util.ts";
 
-export type Unresolved<T extends tg.Value> = MaybePromise<
+export type Unresolved<T extends void | tg.Value> = MaybePromise<
 	T extends
+		| void
 		| undefined
 		| boolean
 		| number
@@ -20,7 +21,8 @@ export type Unresolved<T extends tg.Value> = MaybePromise<
 				: never
 >;
 
-export type Resolved<T extends Unresolved<tg.Value>> = T extends
+export type Resolved<T extends Unresolved<void | tg.Value>> = T extends
+	| void
 	| undefined
 	| boolean
 	| number
diff --git a/packages/runtime/src/target.ts b/packages/runtime/src/target.ts
index 8d41f2307..3fec2a22e 100644
--- a/packages/runtime/src/target.ts
+++ b/packages/runtime/src/target.ts
@@ -14,7 +14,7 @@ export let setCurrentTarget = (target: Target) => {
 
 type FunctionArg<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 > = {
 	function: (...args: A) => tg.Unresolved<R>;
 	module: tg.Module;
@@ -23,15 +23,15 @@ type FunctionArg<
 
 export function target<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 >(arg: FunctionArg): Target<A, R>;
 export function target<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 >(...args: tg.Args<Target.Arg>): Promise<Target<A, R>>;
 export function target<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 >(
 	...args: [FunctionArg<A, R>] | tg.Args<Target.Arg>
 ): MaybePromise<Target<A, R>> {
@@ -70,7 +70,7 @@ export function target<
 
 export interface Target<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 > extends globalThis.Function {
 	(...args: { [K in keyof A]: tg.Unresolved<A[K]> }): Promise<R>;
 }
@@ -78,7 +78,7 @@ export interface Target<
 // biome-ignore lint/suspicious/noUnsafeDeclarationMerging: This is necessary to make targets callable.
 export class Target<
 	A extends Array<tg.Value> = Array<tg.Value>,
-	R extends tg.Value = tg.Value,
+	R extends void | tg.Value = void | tg.Value,
 > extends globalThis.Function {
 	#state: Target.State;
 	#f: Function | undefined;
@@ -116,7 +116,7 @@ export class Target<
 
 	static async new<
 		A extends Array<tg.Value> = Array<tg.Value>,
-		R extends tg.Value = tg.Value,
+		R extends void | tg.Value = void | tg.Value,
 	>(...args: tg.Args<Target.Arg>): Promise<Target<A, R>> {
 		let arg = await Target.arg(...args);
 		let args_ = arg.args ?? [];
diff --git a/packages/runtime/tangram.d.ts b/packages/runtime/tangram.d.ts
index 9704c3631..5ad6a0782 100644
--- a/packages/runtime/tangram.d.ts
+++ b/packages/runtime/tangram.d.ts
@@ -546,17 +546,17 @@ declare namespace tg {
 	/** Create a target. */
 	export function target<
 		A extends Array<tg.Value> = Array<tg.Value>,
-		R extends tg.Value = tg.Value,
+		R extends void | tg.Value = void | tg.Value,
 	>(function_: (...args: A) => tg.Unresolved<R>): tg.Target<A, R>;
 	export function target<
 		A extends Array<tg.Value> = Array<tg.Value>,
-		R extends tg.Value = tg.Value,
+		R extends void | tg.Value = void | tg.Value,
 	>(...args: tg.Args<tg.Target.Arg>): Promise<tg.Target<A, R>>;
 
 	/** A target. */
 	export interface Target<
 		A extends Array<tg.Value> = Array<tg.Value>,
-		R extends tg.Value = tg.Value,
+		R extends void | tg.Value = void | tg.Value,
 	> {
 		/** Build this target. */
 		// biome-ignore lint/style/useShorthandFunctionType: interface is necessary .
@@ -566,7 +566,7 @@ declare namespace tg {
 	/** A target. */
 	export class Target<
 		A extends Array<tg.Value> = Array<tg.Value>,
-		R extends tg.Value = tg.Value,
+		R extends void | tg.Value = void | tg.Value,
 	> extends globalThis.Function {
 		/** Get a target with an ID. */
 		static withId(id: tg.Target.Id): tg.Target;
@@ -940,8 +940,9 @@ declare namespace tg {
 	 * Unresolved<Array<{ key: string }>> = MaybePromise<Array<MaybePromise<{ key: MaybePromise<string> }>>>
 	 * ```
 	 */
-	export type Unresolved<T extends tg.Value> = tg.MaybePromise<
+	export type Unresolved<T extends void | tg.Value> = tg.MaybePromise<
 		T extends
+			| void
 			| undefined
 			| boolean
 			| number
@@ -970,7 +971,8 @@ declare namespace tg {
 	 * Resolved<Promise<Array<Promise<string>>>> = Array<string>
 	 * ```
 	 */
-	export type Resolved<T extends tg.Unresolved<tg.Value>> = T extends
+	export type Resolved<T extends tg.Unresolved<void | tg.Value>> = T extends
+		| void
 		| undefined
 		| boolean
 		| number

From ce5bb371d1554eabb549f203b9f19ef4aea7c714 Mon Sep 17 00:00:00 2001
From: David Yamnitsky <david@yamnitsky.com>
Date: Mon, 25 Nov 2024 16:35:51 -0500
Subject: [PATCH 3/4] remove void from resolved and unresolved

---
 packages/runtime/src/resolve.ts |  8 +++-----
 packages/runtime/src/target.ts  |  6 +++++-
 packages/runtime/tangram.d.ts   | 14 +++++++++-----
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/packages/runtime/src/resolve.ts b/packages/runtime/src/resolve.ts
index 47d31892c..6ac94e725 100644
--- a/packages/runtime/src/resolve.ts
+++ b/packages/runtime/src/resolve.ts
@@ -1,10 +1,9 @@
-import * as im from "immutable";
+import im from "immutable";
 import * as tg from "./index.ts";
 import type { MaybePromise } from "./util.ts";
 
-export type Unresolved<T extends void | tg.Value> = MaybePromise<
+export type Unresolved<T extends tg.Value> = MaybePromise<
 	T extends
-		| void
 		| undefined
 		| boolean
 		| number
@@ -21,8 +20,7 @@ export type Unresolved<T extends void | tg.Value> = MaybePromise<
 				: never
 >;
 
-export type Resolved<T extends Unresolved<void | tg.Value>> = T extends
-	| void
+export type Resolved<T extends Unresolved<tg.Value>> = T extends
 	| undefined
 	| boolean
 	| number
diff --git a/packages/runtime/src/target.ts b/packages/runtime/src/target.ts
index 3fec2a22e..197b0d1ae 100644
--- a/packages/runtime/src/target.ts
+++ b/packages/runtime/src/target.ts
@@ -16,7 +16,11 @@ type FunctionArg<
 	A extends Array<tg.Value> = Array<tg.Value>,
 	R extends void | tg.Value = void | tg.Value,
 > = {
-	function: (...args: A) => tg.Unresolved<R>;
+	function: (
+		...args: A
+	) => R extends void
+		? MaybePromise<void>
+		: tg.Unresolved<Extract<R, tg.Value>>;
 	module: tg.Module;
 	name: string;
 };
diff --git a/packages/runtime/tangram.d.ts b/packages/runtime/tangram.d.ts
index 5ad6a0782..0cb5936e4 100644
--- a/packages/runtime/tangram.d.ts
+++ b/packages/runtime/tangram.d.ts
@@ -547,7 +547,13 @@ declare namespace tg {
 	export function target<
 		A extends Array<tg.Value> = Array<tg.Value>,
 		R extends void | tg.Value = void | tg.Value,
-	>(function_: (...args: A) => tg.Unresolved<R>): tg.Target<A, R>;
+	>(
+		function_: (
+			...args: A
+		) => R extends void
+			? MaybePromise<void>
+			: tg.Unresolved<Extract<R, tg.Value>>,
+	): tg.Target<A, R>;
 	export function target<
 		A extends Array<tg.Value> = Array<tg.Value>,
 		R extends void | tg.Value = void | tg.Value,
@@ -940,9 +946,8 @@ declare namespace tg {
 	 * Unresolved<Array<{ key: string }>> = MaybePromise<Array<MaybePromise<{ key: MaybePromise<string> }>>>
 	 * ```
 	 */
-	export type Unresolved<T extends void | tg.Value> = tg.MaybePromise<
+	export type Unresolved<T extends tg.Value> = tg.MaybePromise<
 		T extends
-			| void
 			| undefined
 			| boolean
 			| number
@@ -971,8 +976,7 @@ declare namespace tg {
 	 * Resolved<Promise<Array<Promise<string>>>> = Array<string>
 	 * ```
 	 */
-	export type Resolved<T extends tg.Unresolved<void | tg.Value>> = T extends
-		| void
+	export type Resolved<T extends tg.Unresolved<tg.Value>> = T extends
 		| undefined
 		| boolean
 		| number

From e50919714a204ccb9e4538287a73f0b26a62c3bf Mon Sep 17 00:00:00 2001
From: David Yamnitsky <david@yamnitsky.com>
Date: Mon, 25 Nov 2024 20:44:22 -0500
Subject: [PATCH 4/4] fix boolean case

---
 packages/runtime/src/resolve.ts | 38 +++++++++++++++------------
 packages/runtime/src/target.ts  |  5 ++--
 packages/runtime/tangram.d.ts   | 46 +++++++++++++++++++--------------
 3 files changed, 50 insertions(+), 39 deletions(-)

diff --git a/packages/runtime/src/resolve.ts b/packages/runtime/src/resolve.ts
index 6ac94e725..a036cdd55 100644
--- a/packages/runtime/src/resolve.ts
+++ b/packages/runtime/src/resolve.ts
@@ -2,23 +2,27 @@ import im from "immutable";
 import * as tg from "./index.ts";
 import type { MaybePromise } from "./util.ts";
 
-export type Unresolved<T extends tg.Value> = MaybePromise<
-	T extends
-		| undefined
-		| boolean
-		| number
-		| string
-		| tg.Object
-		| Uint8Array
-		| tg.Mutation
-		| tg.Template
-		? T
-		: T extends Array<infer U extends tg.Value>
-			? Array<Unresolved<U>>
-			: T extends { [key: string]: tg.Value }
-				? { [K in keyof T]: Unresolved<T[K]> }
-				: never
->;
+export type Unresolved<T extends tg.Value> = MaybePromise<UnresolvedInner<T>>;
+
+export type UnresolvedInner<T extends tg.Value> = T extends
+	| undefined
+	| boolean
+	| number
+	| string
+	| tg.Object
+	| Uint8Array
+	| tg.Mutation
+	| tg.Template
+	? T
+	: T extends Array<infer U extends tg.Value>
+		? Array<Unresolved<U>>
+		: T extends {
+					[key: string]: tg.Value;
+				}
+			? {
+					[K in keyof T]: Unresolved<T[K]>;
+				}
+			: never;
 
 export type Resolved<T extends Unresolved<tg.Value>> = T extends
 	| undefined
diff --git a/packages/runtime/src/target.ts b/packages/runtime/src/target.ts
index 197b0d1ae..5ffc3a755 100644
--- a/packages/runtime/src/target.ts
+++ b/packages/runtime/src/target.ts
@@ -1,4 +1,5 @@
 import * as tg from "./index.ts";
+import type { UnresolvedInner } from "./resolve.ts";
 import {
 	type MaybeMutationMap,
 	type MaybeNestedArray,
@@ -18,9 +19,7 @@ type FunctionArg<
 > = {
 	function: (
 		...args: A
-	) => R extends void
-		? MaybePromise<void>
-		: tg.Unresolved<Extract<R, tg.Value>>;
+	) => MaybePromise<R extends void ? void : UnresolvedInner<Exclude<R, void>>>;
 	module: tg.Module;
 	name: string;
 };
diff --git a/packages/runtime/tangram.d.ts b/packages/runtime/tangram.d.ts
index 0cb5936e4..d541c321a 100644
--- a/packages/runtime/tangram.d.ts
+++ b/packages/runtime/tangram.d.ts
@@ -408,7 +408,9 @@ declare namespace tg {
 	}
 
 	/** Create a symlink. */
-	export let symlink: (arg: tg.Unresolved<tg.Symlink.Arg>) => Promise<tg.Symlink>;
+	export let symlink: (
+		arg: tg.Unresolved<tg.Symlink.Arg>,
+	) => Promise<tg.Symlink>;
 
 	/** A symlink. */
 	export class Symlink {
@@ -550,9 +552,9 @@ declare namespace tg {
 	>(
 		function_: (
 			...args: A
-		) => R extends void
-			? MaybePromise<void>
-			: tg.Unresolved<Extract<R, tg.Value>>,
+		) => MaybePromise<
+			R extends void ? void : tg.UnresolvedInner<Exclude<R, void>>
+		>,
 	): tg.Target<A, R>;
 	export function target<
 		A extends Array<tg.Value> = Array<tg.Value>,
@@ -947,23 +949,29 @@ declare namespace tg {
 	 * ```
 	 */
 	export type Unresolved<T extends tg.Value> = tg.MaybePromise<
-		T extends
-			| undefined
-			| boolean
-			| number
-			| string
-			| tg.Object
-			| Uint8Array
-			| tg.Mutation
-			| tg.Template
-			? T
-			: T extends Array<infer U extends tg.Value>
-				? Array<tg.Unresolved<U>>
-				: T extends { [key: string]: tg.Value }
-					? { [K in keyof T]: tg.Unresolved<T[K]> }
-					: never
+		tg.UnresolvedInner<T>
 	>;
 
+	type UnresolvedInner<T extends tg.Value> = T extends
+		| undefined
+		| boolean
+		| number
+		| string
+		| tg.Object
+		| Uint8Array
+		| tg.Mutation
+		| tg.Template
+		? T
+		: T extends Array<infer U extends tg.Value>
+			? Array<Unresolved<U>>
+			: T extends {
+						[key: string]: tg.Value;
+					}
+				? {
+						[K in keyof T]: Unresolved<T[K]>;
+					}
+				: never;
+
 	/**
 	 * This computed type performs the inverse of `Unresolved`. It takes a type and returns the output of calling `resolve` on a value of that type. Here are some examples:
 	 *