fix: deno writeFile honors open flags

Author: lloydrichards

.changeset/fix-deno-file-system-writes.md

@@ -0,0 +1,5 @@
+---
+"@effect/platform-deno": patch
+---
+
+`DenoFileSystem.writeFile` honors open flags and normalizes already-existing-path errors.

packages/platform-deno/src/DenoFileSystem.ts

@@ -439,17 +439,20 @@ const watch = (
     Stream.unwrap
   )
 
-const writeFile: FileSystem.FileSystem["writeFile"] = (path, data, options) => {
-  const flag = options?.flag
-  return tryPromise("writeFile", path, (signal) =>
-    Deno.writeFile(path, data, {
-      append: flag?.startsWith("a") ?? false,
-      create: flag !== "r" && flag !== "r+",
-      createNew: flag?.includes("x") ?? false,
-      ...(options?.mode === undefined ? {} : { mode: options.mode }),
-      signal
-    }))
-}
+const writeFile: FileSystem.FileSystem["writeFile"] = (path, data, options) =>
+  open(path, { ...options, flag: options?.flag ?? "w" }).pipe(
+    Effect.andThen((file) => data.length === 0 ? Effect.void : file.writeAll(data)),
+    Effect.scoped,
+    Effect.mapError((error) =>
+      error.reason._tag === "BadArgument"
+        ? error
+        : PlatformError.systemError({
+          ...error.reason,
+          method: "writeFile",
+          pathOrDescriptor: path
+        })
+    )
+  )
 
 const makeFileSystem = Effect.map(Effect.serviceOption(FileSystem.WatchBackend), (backend) =>
   FileSystem.make({

packages/platform-deno/src/internal/error.ts

@@ -20,6 +20,7 @@ export const handleError = (
       tag = "PermissionDenied"
       break
     case "BadResource":
+    case "AlreadyExists":
     case "InvalidData":
     case "TimedOut":
     case "UnexpectedEof":