[PATCH v2] Makefile: use sha1collisiondetection by default on OSX and Darwin

When the sha1collisiondetection library was added and made the default in [1] the interaction with APPLE_COMMON_CRYPTO added in [2] and [3] seems to have been missed. On modern OSX and Darwin we are able to use Apple's CommonCrypto both for SHA-1, and as a generic (but partial) OpenSSL replacement.

This left OSX and Darwin without protection against the SHAttered attack when building Git in its default configuration.

Let's also use sha1collisiondetection on OSX, to do so we'll need to split up the "APPLE_COMMON_CRYPTO" flag into that flag and a new "APPLE_COMMON_CRYPTO_SHA1".

Because of this we can stop conflating whether we want to use Apple's CommonCrypto at all, and whether we want to use it for SHA-1. This makes the CI recipe added in [4] simpler.

1. e6b07da2780 (Makefile: make DC_SHA1 the default, 2017-03-17)
2. 4dcd7732db0 (Makefile: add support for Apple CommonCrypto facility, 2013-05-19)
3. 61067954ce1 (cache.h: eliminate SHA-1 deprecation warnings on Mac OS X, 2013-05-19)
4. 1ad5c3df35a (ci: use DC_SHA1=YesPlease on osx-clang job for CI,
   2022-10-20)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
Range-diff against v1:
1:  1f4e39be97b ! 1:  3de7cdbd260 Makefile: use sha1collisiondetection by default on OSX and Darwin
    @@ Commit message
         split up the "APPLE_COMMON_CRYPTO" flag into that flag and a new
         "APPLE_COMMON_CRYPTO_SHA1".
     
    -    Let's also change the CI for "osx-clang" to test with the new
    -    APPLE_COMMON_CRYPTO_SHA1 knob ("osx-gcc" uses the new
    -    sha1collisiondetection default).
    -
    -    In practice this will spot issues like the one noted in [4], as
    -    testing with just two backends should be enough to spot unportable
    -    code. Ideally we'd have other CI jobs to test the various SHA-1
    -    combinations, but for now we have better CI coverage than before.
    +    Because of this we can stop conflating whether we want to use Apple's
    +    CommonCrypto at all, and whether we want to use it for SHA-1.  This
    +    makes the CI recipe added in [4] simpler.
     
         1. e6b07da2780 (Makefile: make DC_SHA1 the default, 2017-03-17)
         2. 4dcd7732db0 (Makefile: add support for Apple CommonCrypto facility, 2013-05-19)
         3. 61067954ce1 (cache.h: eliminate SHA-1 deprecation warnings on Mac OS X, 2013-05-19)
    -    4. 32205655dc7 (fsmonitor OSX: compile with DC_SHA1=YesPlease, 2022-10-19)
    +    4. 1ad5c3df35a (ci: use DC_SHA1=YesPlease on osx-clang job for CI,
    +       2022-10-20)
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    @@ Makefile: include shared.mak
      #
     -# Define NO_APPLE_COMMON_CRYPTO on OSX to opt-out of using the
     -# "APPLE_COMMON_CRYPTO" backend for SHA-1, which is currently the
    --# default on that OS. We'll define NO_APPLE_COMMON_CRYPTO on Mac OS
    --# 10.4 or older ("Tiger", released in early 2005).
    +-# default on that OS. On macOS 01.4 (Tiger) or older,
    +-# NO_APPLE_COMMON_CRYPTO is defined by default.
     +# Define APPLE_COMMON_CRYPTO_SHA1 to use Apple's CommonCrypto for
     +# SHA-1.
      #
    - # === SHA-256 backend ===
    - #
    + # If don't enable any of the *_SHA1 settings in this section, Git will
    + # default to its built-in sha1collisiondetection library, which is a
     @@ Makefile: ifdef NO_POSIX_GOODIES
      	BASIC_CFLAGS += -DNO_POSIX_GOODIES
      endif
    @@ Makefile: ifdef BLK_SHA1
      else
     
      ## ci/lib.sh ##
    -@@ ci/lib.sh: macos-latest)
    - esac
    - 
    - case "$jobname" in
    -+osx-clang)
    -+	MAKEFLAGS="$MAKEFLAGS APPLE_COMMON_CRYPTO_SHA1=Yes"
    -+	;;
    - linux32)
    - 	CC=gcc
    +@@ ci/lib.sh: macos-*)
    + 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=$(which python3)"
    + 	else
    + 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=$(which python2)"
    +-		MAKEFLAGS="$MAKEFLAGS NO_APPLE_COMMON_CRYPTO=NoThanks"
    +-		MAKEFLAGS="$MAKEFLAGS NO_OPENSSL=NoThanks"
    ++		MAKEFLAGS="$MAKEFLAGS APPLE_COMMON_CRYPTO_SHA1=Yes"
    + 	fi
      	;;
    + esac

 Makefile  | 10 ++++------
 ci/lib.sh |  3 +--
 2 files changed, 5 insertions(+), 8 deletions(-)