Fix Deno filesystem error context

.changeset/deno-write-copy-errors.md

@@ -0,0 +1,5 @@
+---
+"@effect/platform-deno": patch
+---
+
+Preserve high-level filesystem error context for `writeFile` and normalize Deno `AlreadyExists` errors from `copy`.

packages/effect/test/FileSystem.test-utils.ts

@@ -1,5 +1,5 @@
 import { assert, expect, it } from "@effect/vitest"
-import { Array } from "effect"
+import { Array, Result } from "effect"
 import * as Effect from "effect/Effect"
 import * as Fs from "effect/FileSystem"
 import type * as Layer from "effect/Layer"
@@ -137,8 +137,11 @@ export const testLayer = <E>(layer: Layer.Layer<Fs.FileSystem, E>, options: Test
       const fs = yield* Fs.FileSystem
       const path = yield* fs.makeTempFile()
 
-      yield* fs.writeFileString(path, "data", { flag: "r" }).pipe(Effect.flip)
+      const error = yield* fs.writeFileString(path, "data", { flag: "r" }).pipe(Effect.flip)
 
+      assert(error.reason._tag !== "BadArgument")
+      assert.strictEqual(error.reason.method, "writeFile")
+      assert.strictEqual(error.reason.pathOrDescriptor, path)
       assert.strictEqual(yield* fs.readFileString(path), "")
     })))
 
@@ -165,6 +168,26 @@ export const testLayer = <E>(layer: Layer.Layer<Fs.FileSystem, E>, options: Test
       assert.strictEqual(yield* fs.readFileString(path), "first")
     })))
 
+  it("copy with overwrite false preserves an existing destination", () =>
+    runPromise(Effect.gen(function*() {
+      const fs = yield* Fs.FileSystem
+      const root = yield* fs.makeTempDirectory()
+      const source = `${root}/source.txt`
+      const destination = `${root}/destination.txt`
+      yield* fs.writeFileString(source, "source")
+      yield* fs.writeFileString(destination, "destination")
+
+      const result = yield* Effect.result(fs.copy(source, destination, { overwrite: false }))
+
+      if (Result.isFailure(result)) {
+        assert(result.failure.reason._tag === "AlreadyExists")
+        assert.strictEqual(result.failure.reason.method, "copy")
+        assert.strictEqual(result.failure.reason.pathOrDescriptor, source)
+      }
+      assert.strictEqual(yield* fs.readFileString(source), "source")
+      assert.strictEqual(yield* fs.readFileString(destination), "destination")
+    })))
+
   it("should track the cursor position when reading", () =>
     runPromise(Effect.gen(function*() {
       const fs = yield* Fs.FileSystem

packages/platform-deno/src/DenoFileSystem.ts

@@ -452,7 +452,14 @@ const writeFile: FileSystem.FileSystem["writeFile"] = (path, data, options) => {
   }
   return Effect.acquireUseRelease(
     tryPromise("writeFile", path, () => Deno.open(path, openOptions(flag, options?.mode))),
-    (file) => new FileImpl(file, flag.startsWith("a")).writeAll(data),
+    (file) =>
+      new FileImpl(file, flag.startsWith("a")).writeAll(data).pipe(
+        Effect.mapError((error) =>
+          error.reason._tag !== "BadArgument"
+            ? PlatformError.systemError({ ...error.reason, method: "writeFile", pathOrDescriptor: path })
+            : error
+        )
+      ),
     (file) => close(file, "writeFile", path)
   )
 }

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

@@ -16,6 +16,9 @@ export const handleError = (
   let tag: SystemErrorTag = "Unknown"
 
   switch (denoError?.name) {
+    case "AlreadyExists":
+      tag = "AlreadyExists"
+      break
     case "NotCapable":
       tag = "PermissionDenied"
       break

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

@@ -9,6 +9,7 @@ describe("handleError", () => {
   const cases: ReadonlyArray<readonly [error: Error, tag: SystemErrorTag]> = [
     [withCode(new Deno.errors.NotFound(), "ENOENT"), "NotFound"],
     [withCode(new Deno.errors.NotADirectory(), "ENOTDIR"), "BadResource"],
+    [new Deno.errors.AlreadyExists(), "AlreadyExists"],
     [withCode(new Deno.errors.AlreadyExists(), "EEXIST"), "AlreadyExists"],
     [withCode(new Deno.errors.IsADirectory(), "EISDIR"), "BadResource"],
     [withCode(new Deno.errors.PermissionDenied(), "EACCES"), "PermissionDenied"],