feat: add isClosed() method to Deno.FsFile

cli/tsc/dts/lib.deno.ns.d.ts

@@ -2239,6 +2239,17 @@ declare namespace Deno {
      * ```
      */
     close(): void;
+    /**
+     * Check if the file is closed.
+     *
+     * ```ts
+     * const file = await Deno.open("my_file.txt");
+     * console.log(file.isClosed()); // false
+     * file.close();
+     * console.log(file.isClosed()); // true
+     * ```
+     */
+    isClosed(): boolean;
 
     [Symbol.dispose](): void;
   }

ext/fs/30_fs.js

@@ -584,6 +584,7 @@ class FsFile {
 
   #readable;
   #writable;
+  #closed = false;
 
   constructor(rid, symbol) {
     ObjectDefineProperty(this, internalRidSymbol, {
@@ -650,6 +651,11 @@ class FsFile {
 
   close() {
     core.close(this.#rid);
+    this.#closed = true;
+  }
+
+  isClosed() {
+    return this.#closed;
   }
 
   get readable() {
@@ -719,6 +725,7 @@ class FsFile {
 
   [SymbolDispose]() {
     core.tryClose(this.#rid);
+    this.#closed = true;
   }
 }
 

tests/unit/files_test.ts

@@ -701,6 +701,49 @@ Deno.test(
   },
 );
 
+Deno.test(
+  { permissions: { read: true } },
+  async function fsFileIsClosed() {
+    const file = await Deno.open("tests/testdata/assets/hello.txt");
+    assertEquals(file.isClosed(), false);
+    file.close();
+    assertEquals(file.isClosed(), true);
+  },
+);
+
+Deno.test(
+  { permissions: { read: true } },
+  function fsFileIsClosedSync() {
+    const file = Deno.openSync("tests/testdata/assets/hello.txt");
+    assertEquals(file.isClosed(), false);
+    file.close();
+    assertEquals(file.isClosed(), true);
+  },
+);
+
+Deno.test(
+  { permissions: { read: true } },
+  async function fsFileIsClosedWithUsing() {
+    let file2: Deno.FsFile;
+    {
+      using file = await Deno.open("tests/testdata/assets/hello.txt");
+      file2 = file;
+      assertEquals(file.isClosed(), false);
+    }
+    assertEquals(file2.isClosed(), true);
+  },
+);
+
+Deno.test(
+  { permissions: { read: true } },
+  async function fsFileIsClosedAfterManualCloseInUsing() {
+    using file = await Deno.open("tests/testdata/assets/hello.txt");
+    assertEquals(file.isClosed(), false);
+    file.close();
+    assertEquals(file.isClosed(), true);
+  },
+);
+
 Deno.test(
   { permissions: { read: true, write: true } },
   function fsFileDatasyncSyncSuccess() {