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.

46 files changed, 57 insertions, 69 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 43340f7..223d737 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "alloc.h"
 
 #include "bfs.h"
diff --git a/src/alloc.h b/src/alloc.h
index 5113839..7b97b8c 100644
--- a/src/alloc.h
+++ b/src/alloc.h
@@ -8,8 +8,6 @@
 #ifndef BFS_ALLOC_H
 #define BFS_ALLOC_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <errno.h>
diff --git a/src/atomic.h b/src/atomic.h
index 5e29974..2682c29 100644
--- a/src/atomic.h
+++ b/src/atomic.h
@@ -8,8 +8,6 @@
 #ifndef BFS_ATOMIC_H
 #define BFS_ATOMIC_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <stdatomic.h>
diff --git a/src/bar.c b/src/bar.c
index c574790..24e51e9 100644
--- a/src/bar.c
+++ b/src/bar.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "bar.h"
 
 #include "alloc.h"
diff --git a/src/bfs.h b/src/bfs.h
index 8820ab9..91c6540 100644
--- a/src/bfs.h
+++ b/src/bfs.h
@@ -8,8 +8,6 @@
 #ifndef BFS_H
 #define BFS_H
 
-#include "prelude.h"
-
 // Standard versions
 
 /** Possible __STDC_VERSION__ values. */
diff --git a/src/bfstd.c b/src/bfstd.c
index 5a6038d..b29fb7b 100644
--- a/src/bfstd.c
+++ b/src/bfstd.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "bfstd.h"
 
 #include "bfs.h"
diff --git a/src/bfstd.h b/src/bfstd.h
index 67894cd..557f253 100644
--- a/src/bfstd.h
+++ b/src/bfstd.h
@@ -8,8 +8,6 @@
 #ifndef BFS_BFSTD_H
 #define BFS_BFSTD_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <stddef.h>
diff --git a/src/bftw.c b/src/bftw.c
index 351cc36..64991b0 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -18,7 +18,6 @@
  *   various helper functions to take fewer parameters.
  */
 
-#include "prelude.h"
 #include "bftw.h"
 
 #include "alloc.h"
diff --git a/src/bit.h b/src/bit.h
index 0c11895..c7530f1 100644
--- a/src/bit.h
+++ b/src/bit.h
@@ -8,8 +8,6 @@
 #ifndef BFS_BIT_H
 #define BFS_BIT_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <limits.h>
diff --git a/src/color.c b/src/color.c
index 0c38c7d..7f653b0 100644
--- a/src/color.c
+++ b/src/color.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "color.h"
 
 #include "alloc.h"
diff --git a/src/color.h b/src/color.h
index 6102480..38f5ad7 100644
--- a/src/color.h
+++ b/src/color.h
@@ -8,8 +8,6 @@
 #ifndef BFS_COLOR_H
 #define BFS_COLOR_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "dstring.h"
 
diff --git a/src/ctx.h b/src/ctx.h
index 0b4be45..e532550 100644
--- a/src/ctx.h
+++ b/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"
diff --git a/src/diag.c b/src/diag.c
index 30525ac..590d45c 100644
--- a/src/diag.c
+++ b/src/diag.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "diag.h"
 
 #include "alloc.h"
diff --git a/src/diag.h b/src/diag.h
index 2d05654..3bea9b2 100644
--- a/src/diag.h
+++ b/src/diag.h
@@ -8,8 +8,6 @@
 #ifndef BFS_DIAG_H
 #define BFS_DIAG_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "bfstd.h"
 
diff --git a/src/dir.c b/src/dir.c
index 0a93fe0..4bf72a1 100644
--- a/src/dir.c
+++ b/src/dir.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "dir.h"
 
 #include "alloc.h"
diff --git a/src/dir.h b/src/dir.h
index 0008d45..4482003 100644
--- a/src/dir.h
+++ b/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>
diff --git a/src/dstring.c b/src/dstring.c
index 2f3abc5..36ed2c7 100644
--- a/src/dstring.c
+++ b/src/dstring.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "dstring.h"
 
 #include "alloc.h"
diff --git a/src/dstring.h b/src/dstring.h
index a6103e3..6d50bc8 100644
--- a/src/dstring.h
+++ b/src/dstring.h
@@ -8,8 +8,6 @@
 #ifndef BFS_DSTRING_H
 #define BFS_DSTRING_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 #include "bfstd.h"
 
diff --git a/src/eval.c b/src/eval.c
index bbafadb..a97c73b 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5,7 +5,6 @@
  * Implementation of all the primary expressions.
  */
 
-#include "prelude.h"
 #include "eval.h"
 
 #include "atomic.h"
diff --git a/src/eval.h b/src/eval.h
index 4dd7996..48184c7 100644
--- a/src/eval.h
+++ b/src/eval.h
@@ -9,8 +9,6 @@
 #ifndef BFS_EVAL_H
 #define BFS_EVAL_H
 
-#include "prelude.h"
-
 struct bfs_ctx;
 struct bfs_expr;
 
diff --git a/src/exec.c b/src/exec.c
index 8f78d7b..45c9f1d 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "exec.h"
 
 #include "alloc.h"
diff --git a/src/expr.h b/src/expr.h
index a6edff1..f14b936 100644
--- a/src/expr.h
+++ b/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"
diff --git a/src/fsade.c b/src/fsade.c
index b10c851..30b3018 100644
--- a/src/fsade.c
+++ b/src/fsade.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "fsade.h"
 
 #include "atomic.h"
diff --git a/src/fsade.h b/src/fsade.h
index 9c7d117..77cf82a 100644
--- a/src/fsade.h
+++ b/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)
diff --git a/src/ioq.c b/src/ioq.c
index 10d4536..f936ff8 100644
--- a/src/ioq.c
+++ b/src/ioq.c
@@ -118,7 +118,6 @@
  * [1]: https://arxiv.org/abs/2201.02179
  */
 
-#include "prelude.h"
 #include "ioq.h"
 
 #include "alloc.h"
diff --git a/src/ioq.h b/src/ioq.h
index 8226941..458c9e7 100644
--- a/src/ioq.h
+++ b/src/ioq.h
@@ -8,8 +8,6 @@
 #ifndef BFS_IOQ_H
 #define BFS_IOQ_H
 
-#include "prelude.h"
-
 #include "dir.h"
 #include "stat.h"
 
diff --git a/src/main.c b/src/main.c
index 9f78522..da07508 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,6 +20,7 @@
  *     - 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)
@@ -27,7 +28,6 @@
  *     - 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"
diff --git a/src/mtab.c b/src/mtab.c
index a013e41..79f3100 100644
--- a/src/mtab.c
+++ b/src/mtab.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "mtab.h"
 
 #include "alloc.h"
diff --git a/src/mtab.h b/src/mtab.h
index 67290c2..6c7d5cb 100644
--- a/src/mtab.h
+++ b/src/mtab.h
@@ -8,8 +8,6 @@
 #ifndef BFS_MTAB_H
 #define BFS_MTAB_H
 
-#include "prelude.h"
-
 struct bfs_stat;
 
 /**
diff --git a/src/opt.c b/src/opt.c
index f75d9c9..425a540 100644
--- a/src/opt.c
+++ b/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"
diff --git a/src/parse.c b/src/parse.c
index a90dc2d..57c60ae 100644
--- a/src/parse.c
+++ b/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"
diff --git a/src/prelude.h b/src/prelude.h
index 5f7203e..a0cc2a1 100644
--- a/src/prelude.h
+++ b/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>
 
diff --git a/src/printf.c b/src/printf.c
index 39abdcc..30ec201 100644
--- a/src/printf.c
+++ b/src/printf.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "printf.h"
 
 #include "alloc.h"
diff --git a/src/pwcache.c b/src/pwcache.c
index 35a9925..c2b575e 100644
--- a/src/pwcache.c
+++ b/src/pwcache.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "pwcache.h"
 
 #include "alloc.h"
diff --git a/src/sanity.h b/src/sanity.h
index 17450a3..0b770cf 100644
--- a/src/sanity.h
+++ b/src/sanity.h
@@ -8,8 +8,6 @@
 #ifndef BFS_SANITY_H
 #define BFS_SANITY_H
 
-#include "prelude.h"
-
 #include <stddef.h>
 
 // Call macro(ptr, size) or macro(ptr, sizeof(*ptr))
diff --git a/src/sighook.c b/src/sighook.c
index d697895..861a0b5 100644
--- a/src/sighook.c
+++ b/src/sighook.c
@@ -17,7 +17,6 @@
  * drop to zero.  Once it does, the old pointer can be safely freed.
  */
 
-#include "prelude.h"
 #include "sighook.h"
 
 #include "alloc.h"
diff --git a/src/stat.c b/src/stat.c
index 9f2918d..e99e711 100644
--- a/src/stat.c
+++ b/src/stat.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "stat.h"
 
 #include "atomic.h"
diff --git a/src/stat.h b/src/stat.h
index a3da1bf..8d0bd9b 100644
--- a/src/stat.h
+++ b/src/stat.h
@@ -12,8 +12,6 @@
 #ifndef BFS_STAT_H
 #define BFS_STAT_H
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 #include <sys/stat.h>
diff --git a/src/thread.c b/src/thread.c
index c555d1f..d61ff8c 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "thread.h"
 
 #include "bfstd.h"
diff --git a/src/thread.h b/src/thread.h
index 7ecda86..7d12468 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -8,8 +8,6 @@
 #ifndef BFS_THREAD_H
 #define BFS_THREAD_H
 
-#include "prelude.h"
-
 #include <pthread.h>
 
 /** Thread entry point type. */
diff --git a/src/trie.c b/src/trie.c
index 848f172..a92950b 100644
--- a/src/trie.c
+++ b/src/trie.c
@@ -81,7 +81,6 @@
  * and insert intermediate singleton "jump" nodes when necessary.
  */
 
-#include "prelude.h"
 #include "trie.h"
 
 #include "alloc.h"
diff --git a/src/version.c b/src/version.c
index 2822927..7479a9f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -1,8 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
-
 #include "bfs.h"
 
 const char bfs_version[] = {
diff --git a/src/xregex.c b/src/xregex.c
index 52f8222..796544e 100644
--- a/src/xregex.c
+++ b/src/xregex.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "xregex.h"
 
 #include "alloc.h"
diff --git a/src/xspawn.c b/src/xspawn.c
index 0b83c8d..b3eed79 100644
--- a/src/xspawn.c
+++ b/src/xspawn.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "xspawn.h"
 
 #include "alloc.h"
diff --git a/src/xspawn.h b/src/xspawn.h
index 60ef1ab..9cfbaf7 100644
--- a/src/xspawn.h
+++ b/src/xspawn.h
@@ -8,8 +8,6 @@
 #ifndef BFS_XSPAWN_H
 #define BFS_XSPAWN_H
 
-#include "prelude.h"
-
 #include <sys/resource.h>
 #include <sys/types.h>
 #include <unistd.h>
diff --git a/src/xtime.c b/src/xtime.c
index 75ace72..dd9b60f 100644
--- a/src/xtime.c
+++ b/src/xtime.c
@@ -1,7 +1,6 @@
 // Copyright © Tavian Barnes <tavianator@tavianator.com>
 // SPDX-License-Identifier: 0BSD
 
-#include "prelude.h"
 #include "xtime.h"
 
 #include "bfs.h"