Hi everyone,

This week, I looked into Macros inside a typedef enum not seen issue.

https://issues.dlang.org/show_bug.cgi?id=24419

After a thorough look into it, I realized the issue had nothing to do with typedef enums.
The real issue was that macros defined in a C file that refer to identifiers could not be resolved when imported from D. when you compile that C file directly, it worked but not when
you import it into a D file to use.

if you have

int a = 6;
 #define num a

num doesn't get to D symbol table because no case was handling identifiers. I attempted that using D aliases to represent C macros that refer to identifiers. my choice of aliases was because it could refer to a variable or a function which is typical in legacy C code.

But the most interesting part is that, my fix ended up in thousands of undefined identifiers when compiling druntime. That was largely due to builtin macros that D had no idea about in the C headers.

I tracked that and realized that was contributing to about 80% to a lot of the macros issues reported. so I had to disable alias creation for __ beginning macros and also macros that had the same fields and also specifiers etc.
like #define if if which semantically had no sense in D but common in C code. but after that I still had few symbols left. I resolved the rest in a small table to check against. now, we can use defines in C that refer to (identifiers) variables and functions.

but I am now researching a lot of the builtins and see a few that could be reasonably defined in importc.h. for this work, I am adding all macro issues to well organize a fix that can help us fully win against macros.

can follow PR here: https://github.com/dlang/dmd/pull/22022