mavgen_cpp11: fix IndexError when an enum entry is a prefix of the enum name

[azrabano23]

What was wrong

mavgen.py --lang=C++11 crashes when an enum contains an entry whose name is a prefix of the enum name (issue #887):

<enum name="SOME_ENUM_NAME">
  <entry value="0" name="SOME_ENUM"/>
</enum>

$ mavgen.py --lang=C++11 --wire-protocol=2.0 -o out test.xml
...
  File ".../pymavlink/generator/mavgen_cpp11.py", line 304, in enum_remove_prefix
    if pl[i] == sl[0]:
IndexError: list index out of range

The C generator handles the same file fine; only the C++11 output is affected.

Root cause

enum_remove_prefix() builds the scoped enum class entry names by popping one leading component of the entry name for each matching component of the enum name. It never checks that at least one component is left, so for SOME_ENUM in SOME_ENUM_NAME the list runs empty after two pops and the third comparison indexes into an empty list. (Even if the loop ended there, the following sl[0][0].isdigit() would fail the same way.)

The fix

Stop stripping once a single component remains, so the entry keeps its last component: SOME_ENUM becomes SOME_ENUM_NAME::ENUM. This is the guard @shancock884 suggested on the issue.

It only changes behaviour for inputs that previously crashed: an entry that used to strip down to exactly one component takes the same path as before. To confirm, I regenerated C++11 headers for message_definitions/v1.0/all.xml before and after the change; all 389 .hpp files are byte-identical (diff -r).

Verification

New tests/test_mavgen_cpp11.py:

• test_enum_remove_prefix: existing cases (MAV_CMD_NAV_WAYPOINT -> NAV_WAYPOINT, the digit case MAV_SYS_STATUS_SENSOR_3D_GYRO -> SENSOR_3D_GYRO) plus the prefix cases from the issue.
• test_cpp11_generator_enum_entry_is_prefix_of_enum_name: runs mavgen.mavgen(..., language="C++11") on a temp XML with the enum above and checks the generated test.hpp contains enum class SOME_ENUM_NAME with ENUM=0 and VALUE=1.

Both fail on master with the IndexError above and pass with this change.

python3 -m pytest tests/test_mavgen_cpp11.py tests/test_mavgen_typescript.py -q   # 3 passed
flake8 generator/mavgen_cpp11.py tests/test_mavgen_cpp11.py --count --select=E9,F63,F7,F82   # 0

Tested with Python 3.12 on macOS.

Fixes #887

🤖 Generated with Claude Code