MFC r307227 and r307343:

  Improve typing of POSIX search tree functions.

  Back in 2015 when I reimplemented these functions to use an AVL tree, I
  was annoyed by the weakness of the typing of these functions. Both tree
  nodes and keys are represented by 'void *', meaning that things like the
  documentation for these functions are an absolute train wreck.

  To make things worse, users of these functions need to cast the return
  value of tfind()/tsearch() from 'void *' to 'type_of_key **' in order to
  access the key. Technically speaking such casts violate aliasing rules.
  I've observed actual breakages as a result of this by enabling features
  like LTO.

  I've filed a bug report at the Austin Group. Looking at the way the bug
  got resolved, they made a pretty good step in the right direction. A new
  type 'posix_tnode' has been added to correspond to tree nodes. It is
  still defined as 'void' for source-level compatibility, but in the very
  far future it could be replaced by a proper structure type containing a
  key pointer.

1 files changed, 3 insertions, 6 deletions

diff --git a/lib/libc/stdlib/twalk.c b/lib/libc/stdlib/twalk.c
index 7acee41..4f999b4 100644
--- a/lib/libc/stdlib/twalk.c
+++ b/lib/libc/stdlib/twalk.c
@@ -4,8 +4,6 @@
  * Tree search generalized from Knuth (6.2.2) Algorithm T just like
  * the AT&T man page says.
  *
- * The node_t structure is for internal use only, lint doesn't grok it.
- *
  * Written by reading the System V Interface Definition, not the code.
  *
  * Totally public domain.
@@ -23,12 +21,11 @@ __FBSDID("$FreeBSD$");
 #include <search.h>
 #include <stdlib.h>
 
-typedef void (*cmp_fn_t)(const void *, VISIT, int);
+typedef void (*cmp_fn_t)(const posix_tnode *, VISIT, int);
 
 /* Walk the nodes of a tree */
 static void
-trecurse(const node_t *root,	/* Root of the tree to be walked */
-	cmp_fn_t action, int level)
+trecurse(const posix_tnode *root, cmp_fn_t action, int level)
 {
 
 	if (root->llink == NULL && root->rlink == NULL)
@@ -46,7 +43,7 @@ trecurse(const node_t *root,	/* Root of the tree to be walked */
 
 /* Walk the nodes of a tree */
 void
-twalk(const void *vroot, cmp_fn_t action) /* Root of the tree to be walked */
+twalk(const posix_tnode *vroot, cmp_fn_t action)
 {
 	if (vroot != NULL && action != NULL)
 		trecurse(vroot, action, 0);