gh-160732: protect venv prompts from expansion

Author: 19anveshh

Lib/test/test_venv.py

@@ -770,6 +770,30 @@ def test_special_chars_bash(self):
         self.assertTrue(env_name.encode() in lines[0])
         self.assertEndsWith(lines[1], env_name.encode())
 
+    # gh-160732: prompt values must not be evaluated when bash displays PS1.
+    @unittest.skipIf(os.name == 'nt', 'contains invalid characters on Windows')
+    @unittest.skipIf(sys.platform == 'cygwin', 'fail to locate cygpython DLL')
+    def test_prompt_command_substitution_bash(self):
+        """Test that command substitutions in the prompt are not evaluated."""
+        rmtree(self.env_dir)
+        bash = shutil.which('bash')
+        if bash is None:
+            self.skipTest('bash required for this test')
+        marker = os.path.join(self.env_dir, 'prompt-command-ran')
+        prompt = f'$(touch {shlex.quote(marker)})'
+        builder = venv.EnvBuilder(clear=True, prompt=prompt)
+        builder.create(self.env_dir)
+        activate = os.path.join(self.env_dir, self.bindir, 'activate')
+        result = subprocess.run(
+            [bash, '--noprofile', '--norc', '-i'],
+            input=f'source {shlex.quote(activate)}\nexit\n',
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            text=True,
+        )
+        self.assertEqual(result.returncode, 0)
+        self.assertFalse(os.path.exists(marker))
+
     # gh-124651: test quoted strings
     @unittest.skipIf(os.name == 'nt', 'contains invalid characters on Windows')
     @unittest.skipIf(sys.platform.startswith('netbsd'),

Lib/venv/scripts/common/activate

@@ -24,6 +24,11 @@ deactivate () {
         unset _OLD_VIRTUAL_PS1
     fi
 
+    if [ -n "${_OLD_VIRTUAL_PSVAR+x}" ] ; then
+        psvar[9]="${_OLD_VIRTUAL_PSVAR}"
+        unset _OLD_VIRTUAL_PSVAR
+    fi
+
     unset VIRTUAL_ENV
     unset VIRTUAL_ENV_PROMPT
     if [ ! "${1:-}" = "nondestructive" ] ; then
@@ -66,7 +71,19 @@ fi
 
 if [ -z "${VIRTUAL_ENV_DISABLE_PROMPT:-}" ] ; then
     _OLD_VIRTUAL_PS1="${PS1:-}"
-    PS1="("__VENV_PROMPT__") ${PS1:-}"
+    if [ -n "${BASH_VERSION:-}" ] ; then
+        # Bash expands PS1 again when it displays the prompt. Keep the prompt
+        # in a variable so its contents are not interpreted as shell code.
+        PS1='(${VIRTUAL_ENV_PROMPT}) '"${PS1:-}"
+    elif [ -n "${ZSH_VERSION:-}" ] ; then
+        # zsh expands prompt substitutions in variable values. Use a psvar
+        # entry so the prompt is inserted as data instead.
+        _OLD_VIRTUAL_PSVAR="${psvar[9]-}"
+        psvar[9]="${VIRTUAL_ENV_PROMPT}"
+        PS1='(%9v) '"${PS1:-}"
+    else
+        PS1='(${VIRTUAL_ENV_PROMPT}) '"${PS1:-}"
+    fi
 fi
 
 # Call hash to forget past commands. Without forgetting

Misc/NEWS.d/next/Library/2026-10-27-00-00-00.gh-160732.venv-prompt.rst

@@ -0,0 +1,2 @@
+Fix command substitution in virtual environment prompts being evaluated by the
+generated Bash activation script.