fix(fs): report read errors of readTextFileLines (#3625)

* fix(fs): report read errors of readTextFileLines

In plugins/fs/src/commands.rs read_text_file_lines_next, a read error was
mapped to "not done, empty line", so a persistent error such as EISDIR
(File::open of a directory succeeds on Unix) made the iterator yield ""
forever and the error was swallowed.

The command now closes the resource and returns the error; the JS iterator
resets its rid so a new iteration starts over. api-iife.js regenerated. E2E
spec iterates a directory and expects a rejection.

* fix(fs): close the file when a readTextFileLines loop exits early

In plugins/fs/guest-js/index.ts readTextFileLines, the async iterator did
not implement return(), so breaking out of a for await loop left the
StdLinesResource (an open file) in the webview resource table.

return() now closes the resource and resets the iterator. api-iife.js
regenerated. E2E spec breaks out of a loop, checks the resource id is no
longer valid and that iterating again starts over.

packages/api-e2e/test/specs/fs.spec.ts

@@ -234,6 +234,57 @@ describePlugin('fs', () => {
     expect(lines).toEqual(['one', 'two', 'three'])
   })
 
+  it('readTextFileLines closes the file when a loop exits early', async () => {
+    const result = await tauri(async (api, path) => {
+      const baseDir = api.fs.BaseDirectory.AppData
+      await api.fs.writeTextFile(path, 'one\ntwo\nthree', { baseDir })
+      const lines = await api.fs.readTextFileLines(path, { baseDir })
+      // the iterator keeps the id of the open file in `rid`
+      const state = lines as unknown as { rid: number | null }
+      let rid: number | null = null
+      let first: string | null = null
+      for await (const line of lines) {
+        first = line
+        rid = state.rid
+        break
+      }
+      let closeError: string | null = null
+      try {
+        await api.core.invoke('plugin:resources|close', { rid })
+      } catch (error) {
+        closeError = String(error)
+      }
+      // iterating again starts over
+      const all: string[] = []
+      for await (const line of lines) {
+        all.push(line)
+      }
+      return { first, ridAfter: state.rid, closeError, all }
+    }, `${dir}/lines-break.txt`)
+    expect(result.first).toBe('one')
+    expect(result.ridAfter).toBeNull()
+    // the resource was already closed by the iterator
+    expect(result.closeError).toMatch(/resource id \d+ is invalid/)
+    expect(result.all).toEqual(['one', 'two', 'three'])
+  })
+
+  it('readTextFileLines rejects when the file cannot be read', async () => {
+    // a directory: opening it fails on Windows, reading it fails elsewhere,
+    // which used to yield empty lines forever
+    const message = await tauriError(async (api, path) => {
+      const baseDir = api.fs.BaseDirectory.AppData
+      await api.fs.mkdir(path, { baseDir, recursive: true })
+      const lines = await api.fs.readTextFileLines(path, { baseDir })
+      for (let i = 0; i < 1000; i++) {
+        const { done } = await lines.next()
+        if (done) return
+      }
+      throw new Error('readTextFileLines kept yielding lines for a directory')
+    }, `${dir}/lines-dir`)
+    expect(message).not.toMatch(/kept yielding/)
+    expect(message).toMatch(/failed to (read line|open file)/)
+  })
+
   it('FileHandle supports write, seek, read, stat and truncate', async () => {
     const result = await tauri(async (api, path) => {
       const baseDir = api.fs.BaseDirectory.AppData