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REDIRECTION_TOKENS mutated by alias/macro create+list (4 locations) -- compounding cross-instance state corruption #1649
Description
Hi cmd2 team — found a module-level state mutation bug in cmd2/cmd2.py while running adversarial test generation via tailtest. One root cause, four copy-pasted source locations, compounding effect across calls.
Bug
Four functions assign constants.REDIRECTION_TOKENS by reference then .extend() it with terminators:
| Function | Line |
|---|---|
_alias_create |
3821 |
_alias_list |
3901 |
_macro_create |
4068 |
_macro_list |
4191 |
Each is shaped like:
tokens_to_unquote = constants.REDIRECTION_TOKENS # reference, not copy
tokens_to_unquote.extend(self.statement_parser.terminators)Every call to these four functions permanently appends terminators to the module-level constants.REDIRECTION_TOKENS. Over multiple calls the list grows without bound:
After 0 calls: ['|', '>', '>>']
After 1 call: ['|', '>', '>>', ';']
After 5 calls: ['|', '>', '>>', ';', ';', ';', ';', ';', ';', ';', ';']
Impact
- Compounding mutation: Each alias/macro create/list call pollutes the global list.
- Cross-instance corruption: Two
Cmd()instances in the same process share the corrupted state. Instance A's alias operations affect instance B's redirection parsing. - Unbounded growth in long-running sessions: Each invocation adds duplicates.
Fix
In all 4 locations, change:
tokens_to_unquote = constants.REDIRECTION_TOKENSto:
tokens_to_unquote = list(constants.REDIRECTION_TOKENS)Reproduction
import pytest
from cmd2 import Cmd
from cmd2 import constants
def test_alias_create_does_not_mutate_redirection_tokens():
"""alias create should not mutate the module-level REDIRECTION_TOKENS list."""
snapshot = list(constants.REDIRECTION_TOKENS)
app = Cmd()
app.onecmd_plus_hooks("alias create myalias echo hello")
assert constants.REDIRECTION_TOKENS == snapshot, (
f"BUG: REDIRECTION_TOKENS mutated by alias create. "
f"Was {snapshot!r}, now {constants.REDIRECTION_TOKENS!r}"
)
def test_repeated_alias_creates_compound_mutation():
"""Compound effect: 5 alias creates should not grow REDIRECTION_TOKENS."""
snapshot = list(constants.REDIRECTION_TOKENS)
app = Cmd()
for i in range(5):
app.onecmd_plus_hooks(f"alias create alias_{i} echo {i}")
assert constants.REDIRECTION_TOKENS == snapshot, (
f"BUG: REDIRECTION_TOKENS grew over 5 alias creates: "
f"{snapshot!r} -> {constants.REDIRECTION_TOKENS!r}"
)
def test_two_instances_alias_create_independence():
"""Two Cmd instances should not share corrupted REDIRECTION_TOKENS state."""
snapshot = list(constants.REDIRECTION_TOKENS)
a = Cmd()
b = Cmd()
a.onecmd_plus_hooks("alias create x echo x")
state_after_a = list(constants.REDIRECTION_TOKENS)
assert state_after_a == snapshot, (
f"BUG: instance A mutated module-level REDIRECTION_TOKENS: "
f"{snapshot!r} -> {state_after_a!r}; instance B sees the corruption"
)Happy to open a PR — it's a 4-line change. Found via tailtest adversarial test generation.
Activity
tleonhardt commentedon Apr 24, 2026
@pramodavansaber Thank you for your well-written bug report! As you said, its a 4-line change, we should be able to incorporate a fix into an upcoming PR that we are working on.
tleonhardt commentedon Apr 24, 2026
#1650 fixes this on the 3.x branch in preparation for a 3.5.1 bug fix release.
We will fix it separately on the
mainbranch to go into 4.0.0.