Comments at end of concatenation macro cause error

[jrt999]

A concatenation macro having a comment at end of same line causes Arduino IDE to fail - appears to be when it is "pasting" for indexing source code. CPP processes the file fine.

Example code

# define RXN 2  /* comment here causes error: pasting ... does not give valid preprocessing token */
# define RXN_BUFHEAD(X)        Rx ## X ## _BufHead
# define Rxn_BUFHEAD(X)        RXN_BUFHEAD(X)
# define Rxn_BufHead           Rxn_BUFHEAD(RXN)

static uint8_t   Rxn_BufHead;  // User read steps on, then takes from buffer

void setup() {

  Rx2_BufHead = 0;
}

void loop() {
}

[thinkyhead]

Seeing this again in Arduino IDE 1.9 beta.
See the issue linked above, for example.
End-of-line comments are converted into block comments and retained as part of the token value instead of being stripped.

sketch\src\module\thermistor/../../inc/../pins/pins_RADDS.h:143:31: error:
pasting "/* BED*/" and "_WPORT" does not give a valid preprocessing token

 #define HEATER_BED_PIN      7 // BED
                               ^

sketch\src\module\thermistor/../../inc/../HAL/HAL_DUE/fastio_Due.h:75:33: note: in definition of macro '_WRITE'
   volatile Pio* port = (DIO ##  IO ## _WPORT); \
                                 ^

sketch\src\module\thermistor/../../inc/Conditionals_post.h:850:31: note: in expansion of macro 'WRITE'
   #define WRITE_HEATER_BED(v) WRITE(HEATER_BED_PIN, (v) ^ HEATER_BED_INVERTING)
                               ^

sketch\src\module\thermistor/../../inc/Conditionals_post.h:850:37: note: in expansion of macro 'HEATER_BED_PIN'
   #define WRITE_HEATER_BED(v) WRITE(HEATER_BED_PIN, (v) ^ HEATER_BED_INVERTING)
                                     ^

sketch\src\module\temperature.cpp:877:11: note: in expansion of macro 'WRITE_HEATER_BED'
           WRITE_HEATER_BED(LOW);
           ^

[matthijskooijman]

Interesting isue. From the error in the last comment, it seems that the preprocessor is converting the // BED comment to /* BED */ so it does not cause issues in most contexts, except for this one.

It does seem this is a compiler bug. From the C++11 (draft) spec (2.2.3):

The source file is decomposed into preprocessing tokens (2.5) and sequences of white-space characters (including comments). A source file shall not end in a partial preprocessing token or in a partial comment. Each comment is replaced by one space character.

This happens before processing preprocessing tokens, so the code shown should compile.

However, I'm not able to reproduce this error with any of the compilers I have at hand here. I do not have the 1.9 beta installed, but I do not believe the arm gcc version is changed there. @thinkyhead, could you show a more self-contained example (or test the example from @jrt999 in your setup) and provide some more details about your setup (what board/core are you using, what core version) and a full verbose compile output (enable in preferences) would also help in reproducing this.

[per1234]

It sounds to me like arduino/arduino-preprocessor#6

EDIT: I'm referring to the issue reported by thinkhead, which only occurs with Arduino IDE 1.9.0 Beta. The code supplied by jrt999 causes an error in Arduino IDE 1.8.5 as well as 1.9.0 beta

[thinkyhead]

Here's a branch of Marlin that should exhibit the issue on build (for RADDS/DUE),
assuming nothing else is exacerbating it:
https://github.com/thinkyhead/Marlin/tree/bf2_radds_pin_error

[jt-github]

This is also an issue in v1.8.9 (also found by trying to compile Marlin, like @thinkyhead)

Example (from https://github.com/MarlinFirmware/Marlin/tree/bugfix-2.0.x/Marlin/src/pins/mega/pins_GT2560_V3.h, line 141):
#define SUICIDE_PIN 54 // This pin must be enabled at boot to keep power flowing

Yields:
error: pasting "/* This pin must be enabled at boot to keep power flowing*/" and "_DDR" does not give a valid preprocessing token