[PATCH v2 05/11] setup: use the default algorithm to initialize repo format

When we define a new repository format with REPOSITORY_FORMAT_INIT, we always use GIT_HASH_SHA1, and this value ends up getting used as the default value to initialize a repository if none of the command line, environment, or config tell us to do otherwise.

Because we might not always want to use SHA-1 as the default, let's instead specify the default hash algorithm constant so that we will use whatever the specified default is.

However, we also need to continue to read older repositories. If we're in a v0 repository or extensions.objectformat is not set, then we must continue to default to the original hash algorithm: SHA-1. If an algorithm is set explicitly, however, it will override the hash_algo member of the repository_format struct and we'll get the right value.

Similarly, if the repository was initialized before Git 0.99.3, then it may lack a core.repositoryformatversion key, and some repositories lack a config file altogether. In both cases, format->version is -1 and we need to assume that SHA-1 is in use.

Because clear_repository_format reinitializes the struct repository_format and therefore sets the hash_algo member to the default (which could in the future not be SHA-1), we need to reset this member explicitly. We know, however, that at the point we call read_repository_format, we are actually reading an existing repository and not initializing a new one or operating outside of a repository, so we are not changing the default behavior back to SHA-1 if the default algorithm is different.

It is potentially questionable that we ignore all repository configuration if there is a config file but it doesn't have core.repositoryformatversion set, in which case we reset all of the configuration to the default. However, it is unclear what the right thing to do instead with such an old repository is and a simple git init will add the missing entry, so for now, we simply honor what the existing code does and reset the value to the default, simply adding our initialization to SHA-1.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
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 setup.c | 5 ++++-
 setup.h | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)