fast-import: introduce "feature notes" command
Here is a 'feature' command for streams to use to require support for
the notemodify (N) command.
When the 'feature' facility was introduced (v1.7.0-rc0~95^2~4,
2009-12-04), the notes import feature was old news (v1.6.6-rc0~21^2~8,
2009-10-09) and it was not obvious it deserved to be a named feature.
But now that is clear, since all major non-git fast-import backends
lack support for it.
Details: on git version with this patch applied, any "feature notes"
command in the features/options section at the beginning of a stream
will be treated as a no-op. On fast-import implementations without
the feature (and older git versions), the command instead errors out
with a message like
This version of fast-import does not support feature notes.
So by declaring use of notes at the beginning of a stream, frontends
can avoid wasting time and other resources when the backend does not
support notes. (This would be especially important for backends that
do not support rewinding history after a botched import.)
Improved-by: Thomas Rast <email@example.com>
Improved-by: Sverre Rabbelier <firstname.lastname@example.org>
Signed-off-by: Jonathan Nieder <email@example.com>
Signed-off-by: Junio C Hamano <firstname.lastname@example.org>