Re: [QUESTION] how to diff one blob with nothing
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Aug 4, 2023, 19:00 UTC
- Message-ID
- <xmqqmsz6ljk4.fsf@gitster.g>
- In-Reply-To
- <ZM1EvGVGv2ZYrpuT@nand.local>
Taylor Blau <me@ttaylorr.com> writes:
Show 22 quoted lines
> On Fri, Aug 04, 2023 at 10:28:53AM +0200, Christian Couder wrote: >> On Fri, Aug 4, 2023 at 6:42 AM ZheNing Hu <adlternative@gmail.com> wrote: >> >> > Actually, there is no need to support a default empty blob. >> > For example, with the command "git diff --no-index <file> /dev/null", >> > it can compare a file with /dev/null, but it can only compare <file> >> > and not <oid>. >> > Therefore, using commands like "git diff <oid> /dev/null", >> > "git diff --no-index <oid> /dev/null", or even "git diff <oid> --stdin" >> > could potentially solve this issue. >> >> Maybe it would be clearer to have a new option, called for example >> "--blob-vs-file", for that then. It could support both: >> >> $ git diff --blob-vs-file <blob> <file> >> >> and: >> >> $ git diff --blob-vs-file <file> <blob> > > Hmm. This feels like a case of trying to teach 'git diff' to do too > much.
Worse yet, I do not quite get the original use case in the first place. What is the series of diff output that result in comparing a random pair of blob object names going to be used for?
The reply to <ZMKtcaN7xYaTtkcI@nand.local> says that the original use case was to express the evolution of a single path since its creation until its removal, but the thing is, a diff with an empty blob and a creation or a deletion event are expressed differently in the patch output, exactly because the patch has to be able to express "before this change, a file with zero byte content was there" and "before this change, there was nothing at this path" (vice versa for contents-removal vs deletion).
For that reason, I have a hard time to find any merit in the earlier complaint that said "can be achieved by manually adding them, but it is not very compatible with the original logic", whatever the "original logic" refers to. If creation needs to be recorded as creation and not as a change from an empty and existing blob, there has to be something that needs to be manually done to turn the latter (which is the only thing "diff" between two blobs or even a blob and a file can give) into the former *anyway*. Whatever the thing that is looping over the history/evoluation of a single path needs to have a three-arm switch for each iteration to deal with creation, modification, and removal, and iterating over the contents of the files and prefixing "+" or "-" on each and every line would be the _easiest_ part of such a necessary tweak to turn "diff between an empty contents and something else" into "creation or deletion of a file."