refactor: use strings.eql instead of std.mem.eql

# Conflicts:
#	test/js/bun/io/bun-write.test.js

src/bun.js/webcore/Blob.zig

@@ -1046,6 +1046,25 @@ pub fn writeFileWithSourceDestination(ctx: *jsc.JSGlobalObject, source_blob: *Bl
     }
     // If this is file <> file, we can just copy the file
     else if (destination_type == .file and source_type == .file) {
+        // Check if source and destination are the same file
+        const dest_pathlike = &destination_store.data.file.pathlike;
+        const src_pathlike = &source_store.data.file.pathlike;
+        if (dest_pathlike.* == .path and src_pathlike.* == .path) {
+            if (strings.eql(dest_pathlike.path.slice(), src_pathlike.path.slice())) {
+                if (source_blob.size == Blob.max_size) {
+                    source_blob.resolveSize();
+                }
+                return jsc.JSPromise.resolvedPromiseValue(ctx, .jsNumber(source_blob.size));
+            }
+        } else if (dest_pathlike.* == .fd and src_pathlike.* == .fd) {
+            if (dest_pathlike.fd == src_pathlike.fd) {
+                if (source_blob.size == Blob.max_size) {
+                    source_blob.resolveSize();
+                }
+                return jsc.JSPromise.resolvedPromiseValue(ctx, .jsNumber(source_blob.size));
+            }
+        }
+
         if (comptime Environment.isWindows) {
             return Blob.copy_file.CopyFileWindows.init(
                 destination_store,

test/js/bun/io/bun-write.test.js

@@ -542,4 +542,97 @@ const IS_UV_FS_COPYFILE_DISABLED =
       expect(await exited).toBe(0);
     }, 10000);
   }
+
+  describe("writing a file to itself", () => {
+    test("should work with its own Bun.file", async () => {
+      using tmpbase = tempDir("bun-write-self-1", {});
+      const tempFilePath = join(tmpbase, `bun-write-self-test.txt`);
+      const content = "Hello, world!";
+
+      const file = Bun.file(tempFilePath);
+      await Bun.write(file, content);
+
+      const fileContent1 = await file.text();
+      expect(fileContent1).toBe(content);
+
+      const size = await Bun.write(file, file);
+      expect(size).toBe(content.length);
+
+      const fileContent2 = await file.text();
+      expect(fileContent2).toBe(content);
+    });
+
+    test("should work with a different reference", async () => {
+      using tmpbase = tempDir("bun-write-self-2", {});
+      const tempFilePath = join(tmpbase, `bun-write-self-test.txt`);
+      const content = "Hello, world!";
+
+      const file1 = Bun.file(tempFilePath);
+      await Bun.write(file1, content);
+
+      const file2 = Bun.file(tempFilePath);
+
+      const size = await Bun.write(file1, file2);
+      expect(size).toBe(content.length);
+
+      const fileContent = await file1.text();
+      expect(fileContent).toBe(content);
+    });
+
+    test("even with just a string path", async () => {
+      using tmpbase = tempDir("bun-write-self-3", {});
+      const tempFilePath = join(tmpbase, `bun-write-self-test.txt`);
+      const content = "Hello, world!";
+
+      const file1 = Bun.file(tempFilePath);
+      await file1.write(content);
+
+      const size = await Bun.write(tempFilePath, file1);
+      expect(size).toBe(content.length);
+
+      const fileContent = await file1.text();
+      expect(fileContent).toBe(content);
+    });
+
+    test("should handle same file descriptor", async () => {
+      using tmpbase = tempDir("bun-write-self-4", {});
+      const tempFilePath = join(tmpbase, `bun-write-self-test.txt`);
+      const content = "Hello, world!";
+
+      const file = Bun.file(tempFilePath);
+      await Bun.write(file, content);
+
+      const fd = fs.openSync(tempFilePath, "r+");
+      const fdFile = Bun.file(fd);
+
+      const size = await Bun.write(fdFile, fdFile);
+      expect(size).toBe(content.length);
+
+      const fileContent = await fdFile.text();
+      expect(fileContent).toBe(content);
+
+      fs.closeSync(fd);
+    });
+
+    // right now it doesn't handle this case
+    test.todo("should handle same file descriptor (2)", async () => {
+      using tmpbase = tempDir("bun-write-self-5", {});
+      const tempFilePath = join(tmpbase, `bun-write-self-test.txt`);
+      const content = "Hello, world!";
+
+      const file = Bun.file(tempFilePath);
+      await Bun.write(file, content);
+
+      const fd = fs.openSync(tempFilePath, "r+");
+      const fdFile = Bun.file(fd);
+
+      const size = await Bun.write(fdFile, file);
+      expect(size).toBe(content.length);
+
+      const fileContent = await fdFile.text();
+      expect(fileContent).toBe(content);
+
+      fs.closeSync(fd);
+    });
+  });
 });