On Tue, Jun 14, 2022 at 10:02:32PM -0400, Taylor Blau wrote:
> --- >8 ---
>
> diff --git a/string-list.h b/string-list.h
> index d5a744e143..425abc55f4 100644
> --- a/string-list.h
> +++ b/string-list.h
> @@ -143,7 +143,7 @@ int for_each_string_list(struct string_list *list,
>
> /** Iterate over each item, as a macro. */
> #define for_each_string_list_item(item,list) \
> - for (item = (list)->items; \
> + for (item = (list) ? (list)->items : NULL; \
> item && item < (list)->items + (list)->nr; \
> ++item)
>
> --- 8< ---
>
> > but even with your suggestion, I get this compiler error:
>
> ...so did I. Though I'm not sure I understand the compiler's warning
> here. Surely the thing being passed as list in the macro expansion
> _won't_ always evaluate to non-NULL, will it?
In the general case, no, but in this specific expansion of the macro, it
is passing the address of a local variable (&cpath), which will never be
NULL. The compiler is overeager here; the check is indeed pointless in
this expansion, but warning on useless macro-expanded code isn't
helpful, since other macro users need it.
Hiding it in a function seems to work, even with -O2 inlining, like:
diff --git a/string-list.h b/string-list.h
index d5a744e143..b28b135e11 100644
--- a/string-list.h
+++ b/string-list.h
@@ -141,9 +141,14 @@ void string_list_clear_func(struct string_list *list, string_list_clear_func_t c
int for_each_string_list(struct string_list *list,
string_list_each_func_t func, void *cb_data);
+static inline struct string_list_item *string_list_first_item(const struct string_list *list)
+{
+ return list ? list->items : NULL;
+}
+
/** Iterate over each item, as a macro. */
#define for_each_string_list_item(item,list) \
- for (item = (list)->items; \
+ for (item = string_list_first_item(list); \
item && item < (list)->items + (list)->nr; \
++item)
-Peff
