The user_libs_all bundler in _resolve_library_components does BFS over the
sketch's external includes, copying each matching Arduino library into
one merged IDF component. Anything not in _BUILTIN_HEADERS is treated as
an external library to resolve, and the lookup just scans
/root/Arduino/libraries/ for a directory whose `src/` (or root) holds a
matching header file.
_BUILTIN_HEADERS only listed C headers (stdint.h, stdio.h, …). The C++
wrappers (cstdint, cstdio, cmath, …) and the STL containers (vector,
complex, string, …) were absent. Result: any library transitively
#including <cstdint> or <vector> caused the bundler to "resolve" the
header against /root/Arduino/libraries/ArduinoSTL/ — an AVR-only
uClibc++ port that ships every C++ stdlib header as plain files. Once
ArduinoSTL was matched the bundler dragged in ALL of it, including
complex.cpp:
template class _UCXXEXPORT complex<float>;
which fails on the ESP-IDF Xtensa toolchain because _UCXXEXPORT isn't
defined in that compile context AND the symbol already exists in the
real libstdc++ pulled in by <complex>. Net effect: every ESP32 sketch
whose deps transitively include a C++ stdlib header (e.g. ESP32Servo
includes <cstdint>) blew up with 66+ errors before the servo example
even reached the link step.
Fix: extend _BUILTIN_HEADERS to cover the full set of C++ stdlib
wrappers and STL headers so the bundler never treats them as installable
libraries. The Xtensa GCC + libstdc++ shipped by ESP-IDF provides them
natively; ArduinoSTL never has any business being part of an ESP32 build.
Verified end-to-end on /example/esp32-servo: compile now succeeds, sketch
boots, moving the potentiometer drives the wokwi-servo angle (Pot=2801 →
Angle=123 deg, servo arm rotates).
dccb70aacd