build: Move feature test macros to prelude.h

This replaces the explicit CPPFLAGS list in flags.mk with just
`-include src/prelude.h`, shortening our compiler command lines and
allowing them to be easily documented.

build/flags.mk

@@ -7,19 +7,7 @@ include build/prelude.mk
 include gen/vars.mk
 
 # Internal flags
-_CPPFLAGS := \
-    -Isrc \
-    -Igen \
-    -D__EXTENSIONS__ \
-    -D_ATFILE_SOURCE \
-    -D_BSD_SOURCE \
-    -D_DARWIN_C_SOURCE \
-    -D_DEFAULT_SOURCE \
-    -D_GNU_SOURCE \
-    -D_POSIX_PTHREAD_SEMANTICS \
-    -D_FILE_OFFSET_BITS=64 \
-    -D_TIME_BITS=64
-
+_CPPFLAGS := -Isrc -Igen -include src/prelude.h
 _CFLAGS := -std=c17 -pthread
 _LDFLAGS :=
 _LDLIBS :=

src/alloc.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "alloc.h"
 
 #include "bfs.h"

src/alloc.h

@@ -8,8 +8,6 @@
 #ifndef BFS_ALLOC_H
 #define BFS_ALLOC_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <errno.h>

src/atomic.h

@@ -8,8 +8,6 @@
 #ifndef BFS_ATOMIC_H
 #define BFS_ATOMIC_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <stdatomic.h>

src/bar.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "bar.h"
 
 #include "alloc.h"

src/bfs.h

@@ -8,8 +8,6 @@
 #ifndef BFS_H
 #define BFS_H
 
-#include "prelude.h"
-
 // Standard versions
 
 /** Possible __STDC_VERSION__ values. */

src/bfstd.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "bfstd.h"
 
 #include "bfs.h"

src/bfstd.h

@@ -8,8 +8,6 @@
 #ifndef BFS_BFSTD_H
 #define BFS_BFSTD_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <stddef.h>

src/bftw.c

@@ -18,7 +18,6 @@
  *   various helper functions to take fewer parameters.
  */
 
-#include "prelude.h"
 #include "bftw.h"
 
 #include "alloc.h"

src/bit.h

@@ -8,8 +8,6 @@
 #ifndef BFS_BIT_H
 #define BFS_BIT_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <limits.h>

src/color.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "color.h"
 
 #include "alloc.h"

src/color.h

@@ -8,8 +8,6 @@
 #ifndef BFS_COLOR_H
 #define BFS_COLOR_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "dstring.h"
 

src/ctx.h

@@ -8,8 +8,6 @@
 #ifndef BFS_CTX_H
 #define BFS_CTX_H
 
-#include "prelude.h"
-
 #include "alloc.h"
 #include "bftw.h"
 #include "diag.h"

src/diag.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "diag.h"
 
 #include "alloc.h"

src/diag.h

@@ -8,8 +8,6 @@
 #ifndef BFS_DIAG_H
 #define BFS_DIAG_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "bfstd.h"
 

src/dir.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "dir.h"
 
 #include "alloc.h"

src/dir.h

@@ -8,8 +8,6 @@
 #ifndef BFS_DIR_H
 #define BFS_DIR_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <sys/types.h>

src/dstring.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "dstring.h"
 
 #include "alloc.h"

src/dstring.h

@@ -8,8 +8,6 @@
 #ifndef BFS_DSTRING_H
 #define BFS_DSTRING_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "bfstd.h"
 

src/eval.c

@@ -5,7 +5,6 @@
  * Implementation of all the primary expressions.
  */
 
-#include "prelude.h"
 #include "eval.h"
 
 #include "atomic.h"

src/eval.h

@@ -9,8 +9,6 @@
 #ifndef BFS_EVAL_H
 #define BFS_EVAL_H
 
-#include "prelude.h"
-
 struct bfs_ctx;
 struct bfs_expr;
 

src/exec.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "exec.h"
 
 #include "alloc.h"

src/expr.h

@@ -8,8 +8,6 @@
 #ifndef BFS_EXPR_H
 #define BFS_EXPR_H
 
-#include "prelude.h"
-
 #include "color.h"
 #include "eval.h"
 #include "stat.h"

src/fsade.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "fsade.h"
 
 #include "atomic.h"

src/fsade.h

@@ -9,8 +9,6 @@
 #ifndef BFS_FSADE_H
 #define BFS_FSADE_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #define BFS_CAN_CHECK_ACL (BFS_HAS_ACL_GET_FILE || BFS_HAS_ACL_TRIVIAL)

src/ioq.c

@@ -118,7 +118,6 @@
  * [1]: https://arxiv.org/abs/2201.02179
  */
 
-#include "prelude.h"
 #include "ioq.h"
 
 #include "alloc.h"

src/ioq.h

@@ -8,8 +8,6 @@
 #ifndef BFS_IOQ_H
 #define BFS_IOQ_H
 
-#include "prelude.h"
-
 #include "dir.h"
 #include "stat.h"
 

src/main.c

@@ -20,14 +20,14 @@
  *     - bftw.[ch]     (an extended version of nftw(3))
  *
  * - Utilities:
+ *     - prelude.h     (feature test macros; automatically included)
  *     - alloc.[ch]    (memory allocation)
  *     - atomic.h      (atomic operations)
  *     - bar.[ch]      (a terminal status bar)
  *     - bit.h         (bit manipulation)
  *     - bfs.h         (configuration and fundamental utilities)
  *     - bfstd.[ch]    (standard library wrappers/polyfills)
  *     - color.[ch]    (for pretty terminal colors)
- *     - prelude.h     (configuration and feature/platform detection)
  *     - diag.[ch]     (formats diagnostic messages)
  *     - dir.[ch]      (a directory API facade)
  *     - dstring.[ch]  (a dynamic string library)
@@ -48,8 +48,6 @@
  *     - xtime.[ch]    (date/time handling utilities)
  */
 
-#include "prelude.h"
-
 #include "bfstd.h"
 #include "ctx.h"
 #include "diag.h"

src/mtab.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "mtab.h"
 
 #include "alloc.h"

src/mtab.h

@@ -8,8 +8,6 @@
 #ifndef BFS_MTAB_H
 #define BFS_MTAB_H
 
-#include "prelude.h"
-
 struct bfs_stat;
 
 /**

src/opt.c

@@ -25,7 +25,6 @@
  * effects are reachable at all, skipping the traversal if not.
  */
 
-#include "prelude.h"
 #include "opt.h"
 
 #include "bfs.h"

src/parse.c

@@ -8,7 +8,6 @@
  * flags like always-true options, and skipping over paths wherever they appear.
  */
 
-#include "prelude.h"
 #include "parse.h"
 
 #include "alloc.h"

src/prelude.h

@@ -2,12 +2,66 @@
 // SPDX-License-Identifier: 0BSD
 
 /**
- * Configuration and feature/platform detection.
+ * Praeludium.
+ *
+ * This header is automatically included in every translation unit, before any
+ * other headers, so it can set feature test macros[1][2].  This sets up our own
+ * mini-dialect of C, which includes
+ *
+ *   - Standard C17 and POSIX.1 2024 features
+ *   - Portable and platform-specific extensions
+ *   - Convenience macros like `bool`, `alignof`, etc.
+ *   - Common compiler extensions like __has_include()
+ *
+ * Further bfs-specific utilities are defined in "bfs.h".
+ *
+ * [1]: https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html
+ * [2]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/V2_chap02.html
  */
 
 #ifndef BFS_PRELUDE_H
 #define BFS_PRELUDE_H
 
+// Feature test macros
+
+/**
+ * Linux and BSD handle _POSIX_C_SOURCE differently: on Linux, it enables POSIX
+ * interfaces that are not visible by default.  On BSD, it also *disables* most
+ * extensions, giving a strict POSIX environment.  Since we want the extensions,
+ * we don't set _POSIX_C_SOURCE.
+ */
+// #define _POSIX_C_SOURCE 202405L
+
+/** openat() etc. */
+#define _ATFILE_SOURCE 1
+
+/** BSD-derived extensions. */
+#define _BSD_SOURCE 1
+
+/** glibc successor to _BSD_SOURCE. */
+#define _DEFAULT_SOURCE 1
+
+/** GNU extensions. */
+#define _GNU_SOURCE 1
+
+/** Use 64-bit off_t. */
+#define _FILE_OFFSET_BITS 64
+
+/** Use 64-bit time_t. */
+#define _TIME_BITS 64
+
+/** macOS extensions. */
+#if __APPLE__
+#  define _DARWIN_C_SOURCE 1
+#endif
+
+/** Solaris extensions. */
+#if __sun
+#  define __EXTENSIONS__ 1
+// https://illumos.org/man/3C/getpwnam#standard-conforming
+#  define _POSIX_PTHREAD_SEMANTICS 1
+#endif
+
 // Get the convenience macros that became standard spellings in C23
 #if __STDC_VERSION__ < 202311L
 
@@ -20,7 +74,7 @@
 
 /**
  * C23 deprecates `noreturn void` in favour of `[[noreturn]] void`, so we expose
- * _noreturn instead with the other attributes.
+ * _noreturn instead with the other attributes in "bfs.h".
  */
 // #include <stdnoreturn.h>
 

src/printf.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "printf.h"
 
 #include "alloc.h"

src/pwcache.c

@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <[email protected]>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "pwcache.h"
 
 #include "alloc.h"