From 89969b4b0bea3bd4cddf97c989ca63f3a1aaa07c Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Mon, 26 May 2025 10:26:12 -0400
Subject: Add support for __attribute__((counted_by(...)))

---
 src/bfs.h     | 9 +++++++++
 src/bftw.c    | 2 +-
 src/color.c   | 4 ++--
 src/dstring.c | 2 +-
 src/ioq.c     | 4 ++--
 src/trie.c    | 2 +-
 src/trie.h    | 2 +-
 7 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/bfs.h b/src/bfs.h
index 32dbbae..3cee727 100644
--- a/src/bfs.h
+++ b/src/bfs.h
@@ -218,6 +218,15 @@ extern const char bfs_ldlibs[];
 #  define _target_clones(...)
 #endif
 
+/**
+ * Mark the size of a flexible array member.
+ */
+#if __has_attribute(counted_by)
+#  define _counted_by(...) __attribute__((counted_by(__VA_ARGS__)))
+#else
+#  define _counted_by(...)
+#endif
+
 /**
  * Optimization hint to not unroll a loop.
  */
diff --git a/src/bftw.c b/src/bftw.c
index 6d1475e..0ca6f34 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -253,7 +253,7 @@ struct bftw_file {
 	/** The length of the file's name. */
 	size_t namelen;
 	/** The file's name. */
-	char name[];
+	char name[]; // _counted_by(namelen + 1)
 };
 
 /**
diff --git a/src/color.c b/src/color.c
index 588dbac..a026831 100644
--- a/src/color.c
+++ b/src/color.c
@@ -32,7 +32,7 @@ struct esc_seq {
 	/** The length of the escape sequence. */
 	size_t len;
 	/** The escape sequence itself, without a terminating NUL. */
-	char seq[];
+	char seq[] _counted_by(len);
 };
 
 /**
@@ -48,7 +48,7 @@ struct ext_color {
 	/** Whether the comparison should be case-sensitive. */
 	bool case_sensitive;
 	/** The extension to match (NUL-terminated). */
-	char ext[];
+	char ext[]; // _counted_by(len + 1);
 };
 
 struct colors {
diff --git a/src/dstring.c b/src/dstring.c
index 0f08679..678d685 100644
--- a/src/dstring.c
+++ b/src/dstring.c
@@ -23,7 +23,7 @@ struct dstring {
 	/** Length of the string, *excluding* the terminating NUL. */
 	size_t len;
 	/** The string itself. */
-	alignas(dchar) char str[];
+	alignas(dchar) char str[] _counted_by(cap);
 };
 
 #define DSTR_OFFSET offsetof(struct dstring, str)
diff --git a/src/ioq.c b/src/ioq.c
index 1efedd7..57eb4a5 100644
--- a/src/ioq.c
+++ b/src/ioq.c
@@ -203,7 +203,7 @@ struct ioqq {
 	cache_align atomic size_t tail;
 
 	/** The circular buffer itself. */
-	cache_align ioq_slot slots[];
+	cache_align ioq_slot slots[]; // _counted_by(slot_mask + 1)
 };
 
 /** Destroy an I/O command queue. */
@@ -593,7 +593,7 @@ struct ioq {
 	/** The number of background threads. */
 	size_t nthreads;
 	/** The background threads themselves. */
-	struct ioq_thread threads[];
+	struct ioq_thread threads[] _counted_by(nthreads);
 };
 
 /** Cancel a request if we need to. */
diff --git a/src/trie.c b/src/trie.c
index 4e0944a..6aac17f 100644
--- a/src/trie.c
+++ b/src/trie.c
@@ -129,7 +129,7 @@ struct trie_node {
 	 * tag to distinguish internal nodes from leaves.  This is safe as long
 	 * as all dynamic allocations are aligned to more than a single byte.
 	 */
-	uintptr_t children[];
+	uintptr_t children[]; // _counted_by(count_ones(bitmap))
 };
 
 /** Check if an encoded pointer is to an internal node. */
diff --git a/src/trie.h b/src/trie.h
index d8cecab..19bd81d 100644
--- a/src/trie.h
+++ b/src/trie.h
@@ -21,7 +21,7 @@ struct trie_leaf {
 	/** The length of the key in bytes. */
 	size_t length;
 	/** The key itself, stored inline. */
-	char key[];
+	char key[] _counted_by(length);
 };
 
 /**
-- 
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