fix(dts/ffi): non-exact types break FFI inference (#14968)

2 files changed, 143 insertions, 30 deletions

diff --git a/cli/dts/lib.deno.unstable.d.ts b/cli/dts/lib.deno.unstable.d.ts
index 643386ced..ab6f8634f 100644
--- a/cli/dts/lib.deno.unstable.d.ts
+++ b/cli/dts/lib.deno.unstable.d.ts
@@ -362,49 +362,60 @@ declare namespace Deno {
 
   export type NativeResultType = NativeType | NativeVoidType;
 
+  type ToNativeTypeMap =
+    & Record<NativeNumberType, number>
+    & Record<NativeBigIntType, bigint | number>
+    & Record<NativePointerType, TypedArray | bigint | null>
+    & Record<NativeFunctionType, bigint | null>;
+
   /** Type conversion for foreign symbol parameters and unsafe callback return types */
-  type ToNativeType<T extends NativeType = NativeType> = T extends
-    NativeNumberType ? number
-    : T extends NativeBigIntType ? bigint | number
-    : T extends NativePointerType ? TypedArray | bigint | null
-    : T extends NativeFunctionType ? bigint | null
-    : never;
+  type ToNativeType<T extends NativeType = NativeType> = ToNativeTypeMap[T];
+
+  type ToNativeResultTypeMap = ToNativeTypeMap & Record<NativeVoidType, void>;
 
   /** Type conversion for unsafe callback return types */
   type ToNativeResultType<T extends NativeResultType = NativeResultType> =
-    T extends NativeType ? ToNativeType<T>
-      : T extends NativeVoidType ? void
+    ToNativeResultTypeMap[T];
+
+  type ToNativeParameterTypes<T extends readonly NativeType[]> =
+    //
+    [(T[number])[]] extends [T] ? ToNativeType<T[number]>[]
+      : [readonly (T[number])[]] extends [T]
+        ? readonly ToNativeType<T[number]>[]
+      : T extends readonly [...NativeType[]] ? {
+          [K in keyof T]: ToNativeType<T[K]>;
+        }
       : never;
 
-  type ToNativeParameterTypes<T extends readonly NativeType[]> = T extends
-    readonly [] ? []
-    : T extends readonly [
-      infer U extends NativeType,
-      ...(infer V extends NativeType[]),
-    ] ? [ToNativeType<U>, ...ToNativeParameterTypes<V>]
-    : never;
+  type FromNativeTypeMap =
+    & Record<NativeNumberType, number>
+    & Record<NativeBigIntType, bigint>
+    & Record<NativePointerType, bigint>
+    & Record<NativeFunctionType, bigint>;
 
   /** Type conversion for foreign symbol return types and unsafe callback parameters */
-  type FromNativeType<T extends NativeType = NativeType> = T extends
-    NativeNumberType ? number
-    : T extends NativeBigIntType | NativePointerType | NativeFunctionType
-      ? bigint
-    : never;
+  type FromNativeType<T extends NativeType = NativeType> = FromNativeTypeMap[T];
+
+  type FromNativeResultTypeMap =
+    & FromNativeTypeMap
+    & Record<NativeVoidType, void>;
 
   /** Type conversion for foregin symbol return types */
   type FromNativeResultType<T extends NativeResultType = NativeResultType> =
-    T extends NativeType ? FromNativeType<T>
-      : T extends NativeVoidType ? void
+    FromNativeResultTypeMap[T];
+
+  type FromNativeParameterTypes<
+    T extends readonly NativeType[],
+  > =
+    //
+    [(T[number])[]] extends [T] ? FromNativeType<T[number]>[]
+      : [readonly (T[number])[]] extends [T]
+        ? readonly FromNativeType<T[number]>[]
+      : T extends readonly [...NativeType[]] ? {
+          [K in keyof T]: FromNativeType<T[K]>;
+        }
       : never;
 
-  type FromNativeParameterTypes<T extends readonly NativeType[]> = T extends
-    readonly [] ? []
-    : T extends readonly [
-      infer U extends NativeType,
-      ...(infer V extends NativeType[]),
-    ] ? [FromNativeType<U>, ...FromNativeParameterTypes<V>]
-    : never;
-
   /** A foreign function as defined by its parameter and result types */
   export interface ForeignFunction<
     Parameters extends readonly NativeType[] = readonly NativeType[],
diff --git a/test_ffi/tests/ffi_types.ts b/test_ffi/tests/ffi_types.ts
index 742f92748..dde08155d 100644
--- a/test_ffi/tests/ffi_types.ts
+++ b/test_ffi/tests/ffi_types.ts
@@ -285,3 +285,105 @@ const static13_right: number = remote.symbols.static13;
 // @ts-expect-error: Invalid member type
 const static14_wrong: null = remote.symbols.static14;
 const static14_right: number = remote.symbols.static14;
+
+// Adapted from https://stackoverflow.com/a/53808212/10873797
+type Equal<T, U> = (<G>() => G extends T ? 1 : 2) extends
+  (<G>() => G extends U ? 1 : 2) ? true
+  : false;
+
+type AssertEqual<
+  Expected extends $,
+  Got extends $$,
+  $ = [Equal<Got, Expected>] extends [true] ? Expected
+    : ([Expected] extends [Got] ? never : Got),
+  $$ = [Equal<Expected, Got>] extends [true] ? Got
+    : ([Got] extends [Expected] ? never : Got),
+> = never;
+
+type AssertNotEqual<
+  Expected extends $,
+  Got,
+  $ = [Equal<Expected, Got>] extends [true] ? never : Expected,
+> = never;
+
+type TypedArray =
+  | Int8Array
+  | Uint8Array
+  | Int16Array
+  | Uint16Array
+  | Int32Array
+  | Uint32Array
+  | Uint8ClampedArray
+  | Float32Array
+  | Float64Array
+  | BigInt64Array
+  | BigUint64Array;
+
+type __Tests__ = [
+  empty: AssertEqual<
+    { symbols: Record<never, never>; close(): void },
+    Deno.DynamicLibrary<Record<never, never>>
+  >,
+  basic: AssertEqual<
+    { symbols: { add: (n1: number, n2: number) => number }; close(): void },
+    Deno.DynamicLibrary<{ add: { parameters: ["i32", "u8"]; result: "i32" } }>
+  >,
+  higher_order_params: AssertEqual<
+    {
+      symbols: {
+        pushBuf: (ptr: bigint | TypedArray | null, func: bigint | null) => void;
+      };
+      close(): void;
+    },
+    Deno.DynamicLibrary<
+      { pushBuf: { parameters: ["pointer", "function"]; result: "void" } }
+    >
+  >,
+  higher_order_returns: AssertEqual<
+    {
+      symbols: {
+        pushBuf: (
+          ptr: bigint | TypedArray | null,
+          func: bigint | null,
+        ) => bigint;
+      };
+      close(): void;
+    },
+    Deno.DynamicLibrary<
+      { pushBuf: { parameters: ["pointer", "function"]; result: "pointer" } }
+    >
+  >,
+  non_exact_params: AssertEqual<
+    {
+      symbols: {
+        foo: (...args: (number | bigint | TypedArray | null)[]) => bigint;
+      };
+      close(): void;
+    },
+    Deno.DynamicLibrary<
+      { foo: { parameters: ("i32" | "pointer")[]; result: "u64" } }
+    >
+  >,
+  non_exact_params_empty: AssertEqual<
+    {
+      symbols: {
+        foo: () => number;
+      };
+      close(): void;
+    },
+    Deno.DynamicLibrary<
+      { foo: { parameters: []; result: "i32" } }
+    >
+  >,
+  non_exact_params_empty: AssertNotEqual<
+    {
+      symbols: {
+        foo: (a: number) => number;
+      };
+      close(): void;
+    },
+    Deno.DynamicLibrary<
+      { foo: { parameters: []; result: "i32" } }
+    >
+  >,
+];