postvariant.h include of Arduino_RouterBridge causes DebugLog 'Serial' not declared error in Zephyr 0.55.0

[hybotix]

With Zephyr 0.55.0, postvariant.h includes Arduino_RouterBridge.h at line 21, which triggers the following transitive include chain inside Arduino.h before Serial is fully defined:

Arduino.h (line 172)
  → postvariant.h (line 21)
    → Arduino_RouterBridge.h (line 16)
      → bridge.h (line 32)
        → Arduino_RPClite.h (line 22)
          → client.h (line 14)
            → error.h (line 20)
              → MsgPack.h (line 5)
                → DebugLog.h (line 17)
                  → DebugLog/Manager.h (line 18)  ← Serial not yet defined

DebugLog/Manager.h line 18 contains:

Stream* stream {&Serial};

This is a non-static data member default initializer that references Serial at header parse time. Because this include chain is now triggered from inside Arduino.h before Serial is defined, compilation fails on any sketch that uses Arduino_RouterBridge — which is mandatory for Zephyr 0.55.0.

Full error output:

In file included from /Arduino/libraries/DebugLog/DebugLog.h:17,
                 from /Arduino/libraries/MsgPack/MsgPack.h:5,
                 from /Arduino/libraries/Arduino_RPClite/src/error.h:20,
                 from /Arduino/libraries/Arduino_RPClite/src/client.h:14,
                 from /Arduino/libraries/Arduino_RPClite/src/Arduino_RPClite.h:22,
                 from /.arduino15/internal/Arduino_RouterBridge_0.4.1_.../src/bridge.h:32,
                 from /.arduino15/internal/Arduino_RouterBridge_0.4.1_.../src/Arduino_RouterBridge.h:16,
                 from /.arduino15/packages/arduino/hardware/zephyr/0.55.0/variants/arduino_uno_q_stm32u585xx/postvariant.h:21,
                 from /.arduino15/packages/arduino/hardware/zephyr/0.55.0/cores/arduino/Arduino.h:172:
/Arduino/libraries/DebugLog/DebugLog/Manager.h:18:26: error: 'Serial' was not declared in this scope; did you mean 'Serial2'?
   18 |         Stream* stream {&Serial};
      |                          ^~~~~~
      |                          Serial2
/Arduino/libraries/DebugLog/DebugLog/Manager.h:18:32: error: cannot convert '<brace-enclosed initializer list>' to 'arduino::Stream*' in initialization
   18 |         Stream* stream {&Serial};
      |                                ^

Steps to reproduce:

1. Install Zephyr platform 0.55.0 on Arduino UNO Q
2. Install Arduino_RouterBridge 0.4.1, Arduino_RPClite 0.2.1, DebugLog 0.8.4
3. Compile any sketch that includes Arduino_RouterBridge.h

Expected behavior:

Compilation succeeds. Serial is available at the point DebugLog/Manager.h is parsed.

Root cause:

Prior to Zephyr 0.55.0, Arduino_RouterBridge.h was only included explicitly by sketches — after Arduino.h had fully initialized Serial. The 0.55.0 introduction of postvariant.h including Arduino_RouterBridge.h from inside Arduino.h broke this assumption for any library that transitively depends on DebugLog. DebugLog 0.8.4 is the latest available version and has no fix for this.

Suggested fix:

Either:

1. Move the Arduino_RouterBridge include in postvariant.h to after Serial is defined in Arduino.h, or
2. Remove the DebugLog dependency from Arduino_RPClite headers — DebugLog should only be pulled in at .cpp level, not through header includes

Environment:

• Board: Arduino UNO Q
• Platform: arduino:zephyr 0.55.0
• Arduino_RouterBridge: 0.4.1
• Arduino_RPClite: 0.2.1
• DebugLog: 0.8.4 (latest)
• OS: Linux arm64

[hybotix]

This problem has me totally stopped on development of my HybX Development System for the UNO Q. Until this is resolved, my development has ceased. https://github.com/hybotix/HybX-Development-System.git

[pillo79]

The dance that allows Serial to be mapped via the Router is very tricky, and this was a known issue during development.

The core includes a stub cores/arduino/DebugLog.h file that is picked by the CLI when building, sidestepping this problem. This is known to be working with the latest IDE/CLI/AppLab; can you confirm what your build system is?

We have submitted hideakitai/DebugLog#26 to fix it properly and it was merged, but the author has not released a newer version to the Library Index, so the above workaround was implemented.

[hybotix]

Thank you! This has enabled me to add detection of upgrades so we should not stumble over this again.