#define of OS breaks #pragma argument in subsequent header file includes

[jonrumsey]

I did this

Whilst developing some code to call the platform APIs on OS/400 to seed a PRNG;
https://www.ibm.com/docs/en/i/7.5?topic=ssw_ibm_i_75/apis/qc3addprngseed.html
These calls fail at runtime with MCH3601 exceptions, this only occurs when first including curl header files.

I expected the following

To be able to include curl headers before or after unrelated header files.

Many OS/400 system header files use pragmas to control how pointers are passed to APIs
https://www.ibm.com/docs/en/i/7.5?topic=descriptions-argument

Unfortunately the platform specific headers in curl (e.g. lib/config-os400.h) define "OS";

/* Define cpu-machine-OS */
#ifndef OS
#define OS "OS/400"
#endif

This gets expanded by the preprocessor and breaks any pragma that uses OS;

    63       |    #pragma argument (Qc3AddPRNGSeed,OS,nowiden)                                                  |  37415   158
    63       +    #pragma argument (Qc3AddPRNGSeed,"OS/400",nowiden)                                            +  37415   158
 ===========> .....................................a............................................................              
 *=WARNING=========> a - CZM0224  Incorrect pragma ignored.                                                                   
    64       |    void Qc3AddPRNGSeed                                                                           |  37416   158
    65       |                    (char *        , /* Seed data                  */                             |  37417   158
    66       |                     unsigned int  , /* Seed length                */                             |  37418   158
    67       |                     void *       ); /* Error Code                 */                             |  37419   158

This impacts any OS/400 headers that are included after curl header files, this can be worked around by including curl headers last or by undefining "OS" before including other headers. A better fix would be to apply a 'CURL_' prefix to the define i.e. 'CURL_OS' so that a string literal is not expanded incorrectly in place of OS.

curl/libcurl version

curl 8.10.1

operating system

OS/400 V7R4M0