Nix Release 2.28.0: Further C++ API Refinements and C API Change

There is no more need to pass `-include` to force additional files to be included. - The public, installed configuration headers no longer contain implementation-specific details that are not relevant to the API. The vast majority of definitions that were previously in there are now moved to new headers that are not installed, but used during Nix's own compilation only. The remaining macro definitions are renamed to have `NIX_` as a prefix. - The name of the Nix component the header comes from (e.g. `util`, `store`, `expr`, `flake`, etc.) is now part of the path to the header, coming after `nix` and before the header name (or rest of the header path, if it is already in a directory). Here is a contrived diff showing a few of these changes at once: ```diff @@ @@ -#include "derived-path.hh" +#include "nix/store/derived-path.hh" @@ @@ +// Would include for the variables used before. But when other headers +// need these variables. those will include these config themselves. +#include "nix/store/config.hh" +#include "nix/expr/config.hh" @@ @@ -#include "config.hh" +// Additionally renamed to distinguish from components' config headers. +#include "nix/util/configuration.hh" @@ @@ -#if HAVE_ACL_SUPPORT +#if NIX_SUPPORT_ACL @@ @@ -#if HAVE_BOEHMGC +#if NIX_USE_BOEHMGC @@ @@ #endif #endif @@ @@ -const char *s = "hi from " SYSTEM; +const char *s = "hi from " NIX_LOCAL_SYSTEM; ``` - C API `nix_flake_init_global` removed [#5638](https://github.com/NixOS/nix/issues/5638) [#12759](https://github.com/NixOS/nix/pull/12759) In order to improve the modularity of the code base, we are removing a use of global state, and therefore the `nix_flake_init_global` function. Instead, use `nix_flake_settings_add_to_eval_state_builder`. For example: ```diff - nix_flake_init_global(ctx, settings); - HANDLE_ERROR(ctx); - nix_eval_state_builder * builder = nix_eval_state_builder_new(ctx, store); HANDLE_ERROR(ctx); + nix_flake_settings_add_to_eval_state_builder(ctx, settings, builder); + HANDLE_ERROR(ctx); ``` Although this change is not as critical, we figured it would be good to do this API change at the same time, also. Also note that we try to keep the C API compatible, but we decided to break this function because it was young and likely not in widespread use yet. This frees up time to make important progress on the rest of the C API. ## Contributors This earlier-than-usual release was made possible by the following 16 contributors: - Farid Zakaria [**(@fzakaria)**](https://github.com/fzakaria) - Jörg Thalheim [**(@Mic92)**](https://github.com/Mic92) - Eelco Dolstra [**(@edolstra)**](https://github.com/edolstra) - Graham Christensen [**(@grahamc)**](https://github.com/grahamc) - Thomas Miedema [**(@thomie)**](https://github.com/thomie) - Brian McKenna [**(@puffnfresh)**](https://github.com/puffnfresh) - Sergei Trofimovich [**(@trofi)**](https://github.com/trofi) - Dmitry Bogatov [**(@KAction)**](https://github.com/KAction) - Erik Nygren [**(@Kirens)**](https://github.com/Kirens) - John Ericson [**(@Ericson2314)**](https://github.com/Ericson2314) - Sergei Zimmerman [**(@xokdvium)**](https://github.com/xokdvium) - Ruby Rose [**(@oldshensheep)**](https://github.com/oldshensheep) - Robert Hensing [**(@roberth)**](https://github.com/roberth) - jade [**(@lf-)**](https://github.com/lf-) - Félix [**(@picnoir)**](https://github.com/picnoir) - Valentin Gagarin [**(@fricklerhandwerk)**](https://github.com/fricklerhandwerk) - Dmitry Bogatov

This chunk details further changes in the Nix 2.28.0 release, continuing the C++ API rework. It specifies that public configuration headers now exclude implementation-specific details, with most definitions moved to internal-only headers and remaining macros renamed with a `NIX_` prefix. Additionally, header paths now include the Nix component name (e.g., `nix/store/config.hh`). The release also removes the C API function `nix_flake_init_global` to improve modularity by eliminating global state, instructing users to migrate to `nix_flake_settings_add_to_eval_state_builder`. This API change was considered acceptable due to the function's relative newness and presumably limited adoption. The section concludes by acknowledging the 16 contributors to this release.