feat(ext/ffi): better type hints for Deno.dlopen (#16874)

1 files changed, 14 insertions, 3 deletions

diff --git a/cli/tsc/dts/lib.deno.unstable.d.ts b/cli/tsc/dts/lib.deno.unstable.d.ts
index ce609736b..9e91c8800 100644
--- a/cli/tsc/dts/lib.deno.unstable.d.ts
+++ b/cli/tsc/dts/lib.deno.unstable.d.ts
@@ -443,7 +443,7 @@ declare namespace Deno {
     /** The definition of the function. */
     definition: Fn;
 
-    constructor(pointer: PointerValue, definition: Fn);
+    constructor(pointer: PointerValue, definition: Const<Fn>);
 
     /** Call the foreign function. */
     call: FromForeignFunction<Fn>;
@@ -494,7 +494,7 @@ declare namespace Deno {
     Definition extends UnsafeCallbackDefinition = UnsafeCallbackDefinition,
   > {
     constructor(
-      definition: Definition,
+      definition: Const<Definition>,
       callback: UnsafeCallbackFunction<
         Definition["parameters"],
         Definition["result"]
@@ -562,6 +562,17 @@ declare namespace Deno {
     close(): void;
   }
 
+  /**
+   *  This magic code used to implement better type hints for {@linkcode Deno.dlopen}
+   */
+  type Cast<A, B> = A extends B ? A : B;
+  type Const<T> = Cast<
+    T,
+    | (T extends string | number | bigint | boolean ? T : never)
+    | { [K in keyof T]: Const<T[K]> }
+    | []
+  >;
+
   /** **UNSTABLE**: New API, yet to be vetted.
    *
    * Opens an external dynamic library and registers symbols, making foreign
@@ -611,7 +622,7 @@ declare namespace Deno {
    */
   export function dlopen<S extends ForeignLibraryInterface>(
     filename: string | URL,
-    symbols: S,
+    symbols: Const<S>,
   ): DynamicLibrary<S>;
 
   /** **UNSTABLE**: New API, yet to be vetted.