Re: [PATCH v3 5/9] i5500-git-daemon.sh: use compile-able version of Git without OpenSSL

On Wed, Sep 11, 2024 at 02:10:10AM -0400, Jeff King wrote:

And here's the fix to make this combo work (and likewise, the "fast" variant). We'd still want the interop fix for the reasons given above, but it feels like one less gotcha for people to hit if they are using OPENSSL_SHA1_FAST.

-- >8 --
Subject: [PATCH] imap-send: handle NO_OPENSSL even when openssl exists

If NO_OPENSSL is defined, then imap-send.c defines a fallback "SSL" type, which is just a void pointer that remains NULL. This works, but it has one problem: it is using the type name "SSL", which conflicts with the upstream name, if some other part of the system happens to include openssl. For example:

  $ make NO_OPENSSL=Nope OPENSSL_SHA1=Yes imap-send.o
      CC imap-send.o
  imap-send.c:35:15: error: conflicting types for ‘SSL’; have ‘void *’
     35 | typedef void *SSL;
        |               ^~~
  In file included from /usr/include/openssl/evp.h:26,
                   from sha1/openssl.h:4,
                   from hash.h:10,
                   from object.h:4,
                   from commit.h:4,
                   from refs.h:4,
                   from setup.h:4,
                   from imap-send.c:32:
  /usr/include/openssl/types.h:187:23: note: previous declaration of ‘SSL’ with type ‘SSL’ {aka ‘struct ssl_st’}
    187 | typedef struct ssl_st SSL;
        |                       ^~~
  make: *** [Makefile:2761: imap-send.o] Error 1

This is not a terribly common combination in practice:

  1. Why are we disabling openssl support but still using its sha1? The
     answer is that you may use the same build options across many
     versions, and some older versions of Git no longer build with
     modern versions of openssl.

  2. Why are we using a totally unsafe sha1 that does not detect
     collisions? You're right, we shouldn't. But in preparation for
     using unsafe sha1 for non-cryptographic checksums, it would be nice
     to be able to turn it on without hassle.

We can make this work by adjusting the way imap-send handles its fallback. One solution is something like this:

  #ifdef NO_OPENSSL
  #define git_SSL void *
  #else
  #define git_SSL SSL
  #endif

But we can observe that we only need this definition in one spot: the struct which holds the variable. So rather than play around with macros that may cause unexpected effects, we can just directly use the correct type in that struct.

Signed-off-by: Jeff King <peff@peff.net>
---
 imap-send.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)