Add typeas() and use it

[alejandro-colomar]

typeas() is safer than typeof() in that it requires that the input is a type name.

And it is more generally useful than (T *){} in that it accepts any type; T* doesn't work with array types nor function types.

(This PR also does a few other changes that are needed before we can use typeas(), and which also make these APIs more readable, safer, and more useful.)

---

• This is a subset of Some improvements to type-safe macros #1388 at v8c.

---

Revisions:

v1b

• Fix commit message. That paragraph was true in the past, but not anymore.

$ git rd 
1:  5413a2a7e = 1:  5413a2a7e lib/: Use a consistent name for macro arguments representing a type name
2:  5de573ad6 ! 2:  c8c014c9b lib/search/, lib/, src/: Add a type parameter to the type-safe macros
    @@ Commit message
         This also makes the code more readable, by having the type explicitly
         stated at call site.
     
    -    There's a slight difference: 'void *' will now be acceptable input.
    -    That shouldn't be an issue.  'void *' is used rarely, so it would be
    -    rare to accidentally pass it where it doesn't belong.  Also, elsewhere
    -    in the language, a void * converts to anything, so making one or two
    -    APIs safe against 'void *' wouldn't change much.
    -
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## lib/addgrps.c ##
3:  fe626d787 = 3:  fea19948c lib/search/: Simplify CMP()
4:  948fb0bb7 = 4:  597e54089 lib/search/: Split APIs
5:  ff3ca8afa = 5:  9e44c0575 lib/sizeof.h: typeas(): Add macro
6:  8e3450183 = 6:  d52ae9d7e lib/{alloc,search}/: Use typeas() to add support for arbitrary types

v1c

• Rebase

$ git rd 
1:  5413a2a7e = 1:  4f95f69bc lib/: Use a consistent name for macro arguments representing a type name
2:  c8c014c9b = 2:  a10273be8 lib/search/, lib/, src/: Add a type parameter to the type-safe macros
3:  fea19948c = 3:  01e68361b lib/search/: Simplify CMP()
4:  597e54089 = 4:  822f7da29 lib/search/: Split APIs
5:  9e44c0575 = 5:  34c1f823a lib/sizeof.h: typeas(): Add macro
6:  d52ae9d7e = 6:  9dd442b84 lib/{alloc,search}/: Use typeas() to add support for arbitrary types

[ikerexxe]

Reopening since this was incorrectly closed

[hallyn]

Holy cow. Github closed the issue that was in the Description? I didn't even
think to manually update that...

[alejandro-colomar]

Holy cow. Github closed the issue that was in the Description? I didn't even think to manually update that...

It's even more funny. I've heard people had closed other projects' issues by having a Closes tag that linked to another repo. Github is quite funny.

[hallyn]

On Fri, Dec 05, 2025 at 06:29:17AM -0800, Alejandro Colomar wrote: What we do is change the selector of _Generic(3). However, it's used as a callback in the same function (think of a macro that expands to just `cmp_int` within the lfind_() call). There, nothing changed.

oh, I see - it's a step more abstract than the way I was processing it. Thank you.