Report cwd failures to the parent process

ptyprocess/ptyprocess.py

@@ -275,30 +275,30 @@ def spawn(
             for pair in zip([2] + spass_fds, spass_fds + [max_fd]):
                 os.closerange(pair[0]+1, pair[1])
 
-            if cwd is not None:
-                os.chdir(cwd)
-
-            if preexec_fn is not None:
-                try:
-                    preexec_fn()
-                except Exception as e:
-                    ename = type(e).__name__
-                    tosend = '{}:0:{}'.format(ename, str(e))
-                    if PY3:
-                        tosend = tosend.encode('utf-8')
-
-                    os.write(exec_err_pipe_write, tosend)
-                    os.close(exec_err_pipe_write)
-                    os._exit(1)
-
             try:
+                if cwd is not None:
+                    os.chdir(cwd)
+
+                if preexec_fn is not None:
+                    try:
+                        preexec_fn()
+                    except Exception as e:
+                        ename = type(e).__name__
+                        tosend = '{}:0:{}'.format(ename, str(e))
+                        if PY3:
+                            tosend = tosend.encode('utf-8')
+
+                        os.write(exec_err_pipe_write, tosend)
+                        os.close(exec_err_pipe_write)
+                        os._exit(1)
+
                 if env is None:
                     os.execv(command, argv)
                 else:
                     os.execvpe(command, argv, env)
             except OSError as err:
-                # [issue #119] 5. If exec fails, the child writes the error
-                # code back to the parent using the pipe, then exits.
+                # [issue #119] 5. If chdir or exec fails, the child writes the
+                # error code back to the parent using the pipe, then exits.
                 tosend = 'OSError:{}:{}'.format(err.errno, str(err))
                 if PY3:
                     tosend = tosend.encode('utf-8')

tests/test_cwd.py

@@ -0,0 +1,72 @@
+import errno
+import os
+import subprocess
+import sys
+import tempfile
+import unittest
+
+from ptyprocess import PtyProcess
+
+
+class CwdTestCase(unittest.TestCase):
+    def _spawn_with_invalid_cwd(self, cwd):
+        # Isolate the call: an unreported child-side exception must not let the
+        # forked child continue running the test suite.
+        code = """
+from ptyprocess import PtyProcess
+import sys
+try:
+    child = PtyProcess.spawn([sys.executable, '-c', 'pass'], cwd=sys.argv[1])
+except OSError as err:
+    print('error:{}'.format(err.errno))
+else:
+    child.close(force=True)
+    print('spawned')
+"""
+        return subprocess.check_output(
+            [sys.executable, '-c', code, cwd],
+            cwd=os.path.dirname(os.path.dirname(__file__)),
+            timeout=10,
+        )
+
+    def test_missing_cwd(self):
+        with tempfile.TemporaryDirectory() as directory:
+            output = self._spawn_with_invalid_cwd(
+                os.path.join(directory, 'missing')
+            )
+        self.assertEqual(output, 'error:{}\n'.format(errno.ENOENT).encode())
+
+    def test_cwd_is_not_a_directory(self):
+        with tempfile.NamedTemporaryFile() as file:
+            output = self._spawn_with_invalid_cwd(file.name)
+        self.assertEqual(output, 'error:{}\n'.format(errno.ENOTDIR).encode())
+
+    def test_valid_cwd_before_preexec(self):
+        original_cwd = os.getcwd()
+        with tempfile.TemporaryDirectory() as directory:
+            def preexec():
+                with open('preexec-marker', 'w') as file:
+                    file.write('ready')
+
+            child = PtyProcess.spawn(
+                [sys.executable, '-c', 'import os; print(os.getcwd())'],
+                cwd=directory,
+                preexec_fn=preexec,
+            )
+            try:
+                output = b''
+                while True:
+                    try:
+                        output += child.read()
+                    except EOFError:
+                        break
+                self.assertEqual(child.wait(), 0)
+            finally:
+                child.close(force=True)
+
+            self.assertEqual(
+                output.strip(), os.fsencode(os.path.realpath(directory))
+            )
+            with open(os.path.join(directory, 'preexec-marker')) as file:
+                self.assertEqual(file.read(), 'ready')
+        self.assertEqual(os.getcwd(), original_cwd)