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Re: [PATCH 2/2] replace-object.c: remove the_repository from prepare_replace_object




On 5/10/2018 7:56 AM, Jeff King wrote:
On Thu, May 10, 2018 at 07:23:13PM +0900, Junio C Hamano wrote:

This one was doing

	ptr = xmalloc(sizeof(*another_ptr))

and it was OK because ptr and another_ptr happened to be of the same
type.  I wonder if we are making it safer, or making it more obscure
to seasoned C programmers, if we introduced a pair of helper macros,
perhaps like these:

	#define ALLOCATE(ptr) (ptr) = xmalloc(sizeof(*(ptr)))
	#define CALLOCATE(ptr,cnt) (ptr) = xcalloc((cnt), sizeof(*(ptr)))
I've often wondered that, too. It's the natural endgame of the
ALLOC_ARRAY() road we've been going down.

I'll chime in that I like this idea.

Because I'm trying to learn more about Coccinelle, I added the diff below and ran 'make coccicheck'. It resulted in a 1000-line patch on 'next'. I'll refrain from sending that patch series, but it's nice to know a "simple" transformation is possible.

Using `git grep` I see 230 instances of 'xmalloc' and 261 instances of 'xcalloc'. After the Coccinelle transformation, these are down to 194 and 190, respectively, because the rest allocate in the same line as the definition. It's worth thinking about the macro pattern for those cases.

diff --git a/contrib/coccinelle/alloc.cocci b/contrib/coccinelle/alloc.cocci
new file mode 100644
index 0000000000..95f426c4dc
--- /dev/null
+++ b/contrib/coccinelle/alloc.cocci
@@ -0,0 +1,13 @@
+@@
+expression p;
+@@
+- p = xmalloc(sizeof(*p));
++ ALLOCATE(p);
+
+@@
+expression c;
+expression p;
+@@
+- p = xcalloc(c, sizeof(*p));
++ CALLOCATE(p,c);
+
diff --git a/git-compat-util.h b/git-compat-util.h
index f9e4c5f9bc..5398f217d7 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -843,6 +843,9 @@ extern FILE *fopen_or_warn(const char *path, const char *mode);
  */
 #define FREE_AND_NULL(p) do { free(p); (p) = NULL; } while (0)

+#define ALLOCATE(ptr) (ptr) = xmalloc(sizeof(*(ptr)))
+#define CALLOCATE(ptr,cnt) (ptr) = xcalloc((cnt), sizeof(*(ptr)))
+
 #define ALLOC_ARRAY(x, alloc) (x) = xmalloc(st_mult(sizeof(*(x)), (alloc)))  #define REALLOC_ARRAY(x, alloc) (x) = xrealloc((x), st_mult(sizeof(*(x)), (alloc)))