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 E2E spec breaks out of a loop, checks the resource id is no
longer valid and that iterating again starts over.

plugins/fs/guest-js/index.ts

@@ -887,10 +887,17 @@ async function readTextFileLines(
         })
       }
 
-      const arr = await invoke<ArrayBuffer | number[]>(
-        'plugin:fs|read_text_file_lines_next',
-        { rid: this.rid }
-      )
+      let arr: ArrayBuffer | number[]
+      try {
+        arr = await invoke<ArrayBuffer | number[]>(
+          'plugin:fs|read_text_file_lines_next',
+          { rid: this.rid }
+        )
+      } catch (error) {
+        // the resource is closed on errors, the next iteration starts over
+        this.rid = null
+        throw error
+      }
 
       const bytes =
         arr instanceof ArrayBuffer ? new Uint8Array(arr) : Uint8Array.from(arr)
@@ -916,6 +923,17 @@ async function readTextFileLines(
       }
     },
 
+    // called when a `for await` loop exits early (`break`, `return` or `throw`)
+    async return(): Promise<IteratorResult<string>> {
+      if (this.rid !== null) {
+        const rid = this.rid
+        this.rid = null
+        // close the file, otherwise it stays open until the webview is destroyed
+        await new Resource(rid).close()
+      }
+      return { value: null, done: true }
+    },
+
     [Symbol.asyncIterator](): AsyncIterableIterator<string> {
       return this
     }

plugins/fs/src/commands.rs

@@ -703,7 +703,12 @@ pub async fn read_text_file_lines_next<R: Runtime>(
                 bytes.push(false as u8);
                 Ok(bytes)
             }
-            Some(Err(_)) => Ok(vec![false as u8]),
+            Some(Err(e)) => {
+                // the error may be persistent (e.g. reading a directory), do not report
+                // an empty line and let the caller loop forever
+                resource_table.close(rid)?;
+                Err(format!("failed to read line with error: {e}").into())
+            }
             None => {
                 resource_table.close(rid)?;
                 Ok(vec![true as u8])