create FLEX_ALLOC_MEM to FLEX_ALLOC_STR cocci rule

I was playing around with coccinelle and I noticed that we have a use of FLEX_ALLOC_MEM that could be converted into FLEX_ALLOC_STR. Convert it and write a cocci rule to prevent this from happening.

Note that this was more of an exercise to teach myself how to use coccinelle. I'm just submitting a useful patch that came as a result of this. Please let me know if this is unwelcome.

Denton Liu (2):
midx.c: convert FLEX_ALLOC_MEM to FLEX_ALLOC_STR
cocci: FLEX_ALLOC_MEM to FLEX_ALLOC_STR

 contrib/coccinelle/flex_alloc.cocci | 13 +++++++++++++
 midx.c                              |  2 +-
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 contrib/coccinelle/flex_alloc.cocci

2.21.0.834.geaa57a21fa

---
 midx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8a505fd423..cb8190329a 100644
@@ -70,7 +70,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 
 	midx_map = xmmap(NULL, midx_size, PROT_READ, MAP_PRIVATE, fd, 0);
 
-	FLEX_ALLOC_MEM(m, object_dir, object_dir, strlen(object_dir));
+	FLEX_ALLOC_STR(m, object_dir, object_dir);
 	m->fd = fd;
 	m->data = midx_map;
 	m->data_len = midx_size;

2.21.0.834.geaa57a21fa

Ensure that a FLEX_MALLOC_MEM that uses 'strlen' for its 'len' uses FLEX_ALLOC_STR instead, since these are equivalent forms.

---
 contrib/coccinelle/flex_alloc.cocci | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 contrib/coccinelle/flex_alloc.cocci

new file mode 100644
index 0000000000..e9f7f6d861
@@ -0,0 +1,13 @@
+@@
+expression str;
+identifier x, flexname;
+@@
+- FLEX_ALLOC_MEM(x, flexname, str, strlen(str));
++ FLEX_ALLOC_STR(x, flexname, str);
+
+@@
+expression str;
+identifier x, ptrname;
+@@
+- FLEXPTR_ALLOC_MEM(x, ptrname, str, strlen(str));
++ FLEXPTR_ALLOC_STR(x, ptrname, str);

2.21.0.834.geaa57a21fa

Both look pretty reasonable to me. Obviously it's a pretty trivial change, but that's sort of the point: automate these things away so we don't have to think about them during review.

Now if you could figure out a way to point people to FLEX_ALLOC in the first place when they are not currently using it, _that_ would be pretty amazing. But I suspect it's a bit too complicated. :)

-Peff