Re: [PATCH 4/4] imap-send: use curl by default

[Jeff King <peff@peff.net>]

On Mon, Aug 07, 2017 at 04:04:05PM +0200, Nicolas Morey-Chaisemartin wrote:

> Signed-off-by: Nicolas Morey-Chaisemartin <nicolas@morey-chaisemartin.com>

Thanks for moving forward with this.

Can you please flesh out your commit messages with some of the reasoning
and related discussion? I know from a nearby thread why we want to flip
the default, but people reading `git log` much later will not have that
context.

> diff --git a/imap-send.c b/imap-send.c
> index 90b8683ed..4ebc16437 100644
> --- a/imap-send.c
> +++ b/imap-send.c
> @@ -35,13 +35,7 @@ typedef void *SSL;
>  #include "http.h"
>  #endif
>  
> -#if defined(USE_CURL_FOR_IMAP_SEND) && defined(NO_OPENSSL)
> -/* only available option */
>  #define USE_CURL_DEFAULT 1
> -#else
> -/* strictly opt in */
> -#define USE_CURL_DEFAULT 0
> -#endif

I agree with the comments Martin made here. I think there are really two
levels of "default" we need to care about:

  1. Build-time: do we default to requiring curl if you want imap-send
     at all?

  2. Run-time: if build with both implementations, which do we use by
     default? Related, if there is only one implementation, what should
     the default be?

I think the answer to (1) is that we still want to build imap-send
without USE_CURL_FOR_IMAP_SEND if the user doesn't have curl installed.
And your patch leaves that, which is good. Though if we are deprecating
it, we may want to issue a deprecation warning (eventually; we can still
switch the run-time default now, get more data on whether a
deprecation/switch is a good idea, and then later decide to deprecate).

For (2), you're trying to switch the default when both are built. But I
think it's important to continue to default to the old-style
implementation if that's the only thing that was built. Otherwise it
effectively becomes the build-time deprecation warning, and we're not
quite ready for that.

So I think this maybe needs to be:

  #if defined(USE_CURL_FOR_IMAP_SEND)
  /* Always default to curl if it's available. */
  #define USE_CURL_DEFAULT 1
  #else
  /* We don't have curl, so continue to use the historical implementation */
  #define USE_CURL_DEFAULT 0
  #endif

-Peff