[libc++][Modules] Restore the <string> include to <__format/format_functions.h>

[iana]

Summary

<__format/format_functions.h> was using <string>, we need to bring the include back that was removed in D154122.

[Mordante]

I think the change is the wrong direction. std::format returns a std::string. In my experience arguments and return values often need to be explicitly exported. So I think the proper fix would be to include string in this header. The main issue is that accidentally forgotten headers worked in the past.

[iana]

In D155116#4501194, @Mordante wrote:

I think the change is the wrong direction. std::format returns a std::string. In my experience arguments and return values often need to be explicitly exported. So I think the proper fix would be to include string in this header. The main issue is that accidentally forgotten headers worked in the past.

But you just barely removed that include in D154122

[iana]

In D155116#4501682, @iana wrote:

In D155116#4501194, @Mordante wrote:

I think the change is the wrong direction. std::format returns a std::string. In my experience arguments and return values often need to be explicitly exported. So I think the proper fix would be to include string in this header. The main issue is that accidentally forgotten headers worked in the past.

But you just barely removed that include in D154122

Then again, the CI says you're right and the include is needed.

[iana]

Restore the <string> include to <__format/format_functions.h> instead

[Mordante]

In D155116#4501682, @iana wrote:

In D155116#4501194, @Mordante wrote:

I think the change is the wrong direction. std::format returns a std::string. In my experience arguments and return values often need to be explicitly exported. So I think the proper fix would be to include string in this header. The main issue is that accidentally forgotten headers worked in the past.

But you just barely removed that include in D154122

That seems like a mistake on my side.

Thanks for the patch, LGTM!

libcxx/include/module.modulemap.in

module __format {
       module format_arg_store                { private header "__format/format_arg_store.h" }
       module format_args                     { private header "__format/format_args.h" }
       module format_context {
         private header "__format/format_context.h"
         export optional
         export locale
       }
       module format_error                    { private header "__format/format_error.h" }
-      module format_functions                {
-        private header "__format/format_functions.h"
-        export string
-      }
+      module format_functions                { private header "__format/format_functions.h" }
       module format_fwd                      { private header "__format/format_fwd.h" }
       module format_parse_context            { private header "__format/format_parse_context.h" }
       module format_string                   { private header "__format/format_string.h" }
       module format_to_n_result {
         private header "__format/format_to_n_result.h"
         export iterator.__iterator.incrementable_traits
       }
       module formatter                       { private header "__format/formatter.h" }