[PATCH] tree-walk.c: fix some sparse 'NULL pointer' warnings

Commit 811cd77b ("tree-walk: learn get_tree_entry_follow_symlinks",
14-05-2015) introduced a new function to locate an object by path
while following symlinks in the repository. However, sparse now
issues some "Using plain integer as NULL pointer" warnings as
follows:

      SP tree-walk.c
  tree-walk.c:517:31: warning: Using plain integer as NULL pointer
  tree-walk.c:521:28: warning: Using plain integer as NULL pointer

The first warning relates to the use of an '{0}' initializer for
the 'struct tree_desc' t. The first field of this structure has
pointer type. A simple solution would replace the initializer
expression with '{NULL}'. However, we choose to remove the
initializer expression and make the initialization more explicit
with a call to the 'init_tree_desc' function.

The second warning relates to the '0' initializer for the buf
field of the 'result_path' strbuf pointer. A simple solution
would replace this initializer with 'NULL'. However, this would
violate a strbuf invariant that the 'buf' field is never NULL.
(see strbuf documentation in strbuf.h header.) Assuming the
documentation of 'get_tree_entry_follow_symlinks' regarding the
'result_path' parameter is observed by callers (ie that the
parameter points to an _unitialized_ strbuf), a better solution
is to simply call the 'strbuf_init' function.

Signed-off-by: Ramsay Jones <redacted>
---

Hi David,

If you need to re-roll the patches in your 'dt/cat-file-follow-symlinks'
branch, could you please squash this, or something like this, into the
relevant patch (commit 811cd77b).

Thanks!

ATB,
Ramsay Jones

 tree-walk.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tree-walk.c b/tree-walk.c
index 8031f3a..6dccd2d 100644
--- a/tree-walk.c
+++ b/tree-walk.c

@@ -514,13 +514,12 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s
 	ssize_t parents_nr = 0;
 	unsigned char current_tree_sha1[20];
 	struct strbuf namebuf = STRBUF_INIT;
-	struct tree_desc t = {0};
+	struct tree_desc t;
 	int follows_remaining = GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS;
 	int i;
 
-	result_path->buf = 0;
-	result_path->alloc = 0;
-	result_path->len = 0;
+	init_tree_desc(&t, NULL, 0UL);
+	strbuf_init(result_path, 0);
 	strbuf_addstr(&namebuf, name);
 	hashcpy(current_tree_sha1, tree_sha1);
 

-- 
2.4.0