From 37f6e09589c44b455571a1f1876cec364b5e0fab Mon Sep 17 00:00:00 2001
From: James Garbutt <43081j@users.noreply.github.com>
Date: Wed, 25 Jun 2025 07:27:33 +0100
Subject: [PATCH] Avoid closing files multiple times in
 `getInterpreter`(#17665)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: fisker Cheung <lionkay@gmail.com>
---
 changelog_unreleased/misc/17665.md |  8 ++++++++
 src/utils/get-interpreter.js       | 29 +++++++++++------------------
 2 files changed, 19 insertions(+), 18 deletions(-)
 create mode 100644 changelog_unreleased/misc/17665.md

diff --git a/changelog_unreleased/misc/17665.md b/changelog_unreleased/misc/17665.md
new file mode 100644
index 000000000..dc24692c9
--- /dev/null
+++ b/changelog_unreleased/misc/17665.md
@@ -0,0 +1,8 @@
+#### Avoid closing files multiple times (#17665 by @43081j)
+
+When reading a file to infer the interpreter from a shebang, we use the
+`n-readlines` library to read the first line in order to get the shebang.
+
+This library closes files when it reaches EOF, and we later try close the same
+files again. We now close files only if `n-readlines` did not already close
+them.
diff --git a/src/utils/get-interpreter.js b/src/utils/get-interpreter.js
index 36aac44ae..f980abd66 100644
--- a/src/utils/get-interpreter.js
+++ b/src/utils/get-interpreter.js
@@ -1,4 +1,3 @@
-import fs from "node:fs";
 import readlines from "n-readlines";
 
 /**
@@ -6,17 +5,17 @@ import readlines from "n-readlines";
  * @returns {string | undefined}
  */
 function getInterpreter(file) {
-  let fd;
   try {
-    fd = fs.openSync(file, "r");
-  } catch {
-    /* c8 ignore next */
-    return;
-  }
+    const liner = new readlines(file);
+    const firstLineBuffer = liner.next();
 
-  try {
-    const liner = new readlines(fd);
-    const firstLine = liner.next().toString("utf8");
+    if (firstLineBuffer === false) {
+      return;
+    }
+
+    liner.close();
+
+    const firstLine = firstLineBuffer.toString("utf8");
 
     // #!/bin/env node, #!/usr/bin/env node
     const m1 = firstLine.match(/^#!\/(?:usr\/)?bin\/env\s+(\S+)/u);
@@ -29,14 +28,8 @@ function getInterpreter(file) {
     if (m2) {
       return m2[1];
     }
-  } finally {
-    try {
-      // There are some weird cases where paths are missing, causing Jest
-      // failures. It's unclear what these correspond to in the real world.
-      fs.closeSync(fd);
-    } catch {
-      // noop
-    }
+  } catch {
+    // couldn't open the file
   }
 }