# GEBS - the Good Enough Build System

GEBS is a reiteration of my previous build system "MIBS" (or MIni Build System). It takes some inspiration from
[Tsoding's](https://twitch.tv/tsoding) [nobuild](https://github.com/tsoding/nobuild) and later on [nob.h](https://github.com/tsoding/nob.h).
The key difference is the way GEBS is implemented on the inside, which makes it more powerful and extensible than nob.h.
GEBS also includes a bunch of extra helper macros, which turn C into a language more akin to Go or Zig, but more on that later.

## So what makes GEBS different?

### Allocators

So one thing I've noticed is that nob.h is used alongside of [arena](https://github.com/tsoding/arena). If you look into the implementation
you can see some things, which are somewhat redundant like \`arena_sprintf()\` or \`arena_da_append()\`, \`arena_sb_append_cstr()\` and so on...
First of all, why is an arena library managing string builders and dynamic arrays? In my opinion it should be the other way around.
A string builder should rather accept a generic allocator interface, which it can then utilize to get it's memory.
Basically we supplement a dynamic structure with an allocator of choice.
In GEBS this is done via a \`Gebs_Allocator\` interface.

\`\`\`c
typedef struct {
    void *(*malloc)(void *self, size_t size);
    void (*free)(void *self, void *memory);
    void *(*realloc)(void *self, void *memory, size_t prev_size, size_t new_size);
} Gebs_Allocator;

// Wrapper macros
#define gebs_malloc(alloc, size) ((alloc)->malloc((void *)(alloc), (size)))
#define gebs_free(alloc, memory) ((alloc)->free((void *)(alloc), (memory)))
#define gebs_realloc(alloc, memory, prev_size, new_size) \
    ((alloc)->realloc((void *)(alloc), (memory), (prev_size), (new_size)))
\`\`\`

We then can implement an allocator that conforms to this interface and it will work with any dynamic structure. 
This is my version of the \`XXX_da_append()\` macro:

\`\`\`c
#define gebs_list_append_alloc(alloc, list, item) \\
    do { \\
        if ((list)->items == nil) { \\
            (list)->capacity = 1; \\
            (list)->items = gebs_malloc((alloc), \\
                                       sizeof(*(list)->items) * (list)->capacity); \\
        } else { \\
            if ((list)->count == (list)->capacity) { \\
                size_t __prev_capacity = (list)->capacity; \\
                (list)->capacity *= 2; \\
                (list)->items = gebs_realloc((alloc), (list)->items, \\
                                            sizeof(*(list)->items) * __prev_capacity, \\
                                            sizeof(*(list)->items) * (list)->capacity); \\
            } \\
        } \\
        (list)->items[(list)->count++] = (item); \\
    } while(0)

#define gebs_list_append(list, item) \\
    gebs_list_append_alloc(&gebs_default_allocator, (list), (item))
\`\`\`

This way a dynamic list can work with any kind of allocator - the default libc allocator, an arena or literally anything else.
We're not tied to the libc allocator and then have to implement the same macro of all other allocators.

### Defer macro

Ever forgot to place a \`free()\` call on function exit or an \`fclose()\`? The defer macro comes to the rescue. Here's a short snippet:
(Taken straight form the source code of this website btw.)

\`\`\`c
    cJSON *root = cJSON_CreateObject();
    defer { cJSON_Delete(root); }

    char *time = __TIME__;
    uchar md5_buf[16];
    md5String(time, md5_buf);
    String_Builder sb = {0};
    defer { sb_free(&sb); }
    for (size_t i = 0; i < 16; i++) {
        sb_append_nstr(&sb, fmt("%02x", md5_buf[i]));
    }
    sb_finish(&sb);

    cJSON_AddItemToObject(root, "build_id", cJSON_CreateString(sb.items));

    make_application_json(result, 200, root);
\`\`\`

If not for the \`defer { ... }\` macro, remebering when to free memory would have been quite hellish.
Another example:

\`\`\`c
    NString_List env = {0};
    defer { list_free(&env); }

    String_Builder out = {0};
    defer { sb_free(&out); }

    char path[PATH_MAX] = {0};
    if (!get_baked_resource_path("home.html", path, sizeof(path))) {
        make_internal_server_error(result);
        return;
    }
\`\`\`

On \`return\` we'd have to **NOT FORGET** to add \`list_free()\` and \`sb_free()\`, but now that we have our defer,
we can kind of shut the brain off and not concern ourselves with freeing the memory. We can be 100% sure it's going to
be freed if we step into the return statement.

The implementation is quite simple, actually

\`\`\`
#define defer defer__2(__COUNTER__)
#define defer__2(X) defer__3(X)
#define defer__3(X) defer__4(defer__id##X)
#define defer__4(ID) auto void ID##func(char (*)[]); __attribute__((cleanup(ID##func))) char ID##var[0]; void ID##func(char (*ID##param)[])
\`\`\`

Source article: https://gustedt.wordpress.com/2025/01/06/simple-defer-ready-to-use/

### compile_flags.txt

Clang/LLVM docs: https://clang.llvm.org/docs/JSONCompilationDatabase.html

I use clangd inside of my vim. Clangd can be configured via a json database compile_commands.json. It's quite complicated for GEBS in a sense
that it uses the \`XX.c -> XX.o\` building pattern, while GEBS is focused more on unity builds (it's on the programmer to implement caching).
Luckily, clangd can be configured via a simple and minimalistic config file - \`compile_flags.txt\`, which holds only compiler flags that
are used to compile our C files. We can for eg. put some include paths in there and clangd will pick them up.

In GEBS we can generate a \`compile_flags.txt\` file using a built-in macro:

\`\`\`c
    #define CFLAGS \\
        "-I.", \\
        "-I./some-lib", \\
        "-Wall", \\
        "-Wextra" \\

    // #define other stuff like CC, LDFLAGS, SOURCES

    make_compile_flags(CFLAGS); // Will output the file
\`\`\`