Junio C Hamano <gitster@xxxxxxxxx> 于2023年8月5日周六 03:00写道： > > Taylor Blau <me@xxxxxxxxxxxx> writes: > > > 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@xxxxxxxxx> 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." > Okay, let me clarify the background for using an empty blob diff. Essentially, it is a git web diff interface that requires real-time calculation of the diff between files across multiple versions and rendering them. Due to some reasons, the higher-level component did not provide multiple versions of commits but instead provided blob OIDs (Object IDs). Therefore, I expected to generate the diff results directly using the "git diff <oid> <oid>" command. (I only care about the patch part in the diff and don't really care about the related information of OIDs in the diff output.) Everything went smoothly except when a blob is created or deleted, as there is no direct way to obtain the diff for a blob using the "git diff <oid> <oid>" interface. Initially, I intended to generate a patch by diffing an empty blob (e69de29bb2d1d6434b8b29ae775ad8c2e48c5391) with the blob ID. However, unlike the empty tree (4b825dc642cb6eb9a060e54bf8d69288fbee4904), the empty blob does not exist in the git repository by default. I had to create an additional empty blob for the purpose of performing the diff, but this goes against the design of the web-based diff interface, which is intended to be read-only. So, I might explore methods like "git diff <oid> /dev/null" or "git diff <oid> --stdin", they are read only, but it does not currently exist... Regardless, I hope that the empty blob diff can simulate the effect of an empty tree diff: git diff 4b825dc642cb6eb9a060e54bf8d69288fbee4904 diff --git a/.cirrus.yml b/.cirrus.yml new file mode 100644 index 0000000000..4860bebd32 --- /dev/null +++ b/.cirrus.yml @@ -0,0 +1,22 @@ +env: + CIRRUS_CLONE_DEPTH: 1 + +freebsd_12_task: + env: + GIT_PROVE_OPTS: "--timer --jobs 10" + GIT_TEST_OPTS: "--no-chain-lint --no-bin-wrappers" + MAKEFLAGS: "-j4" + DEFAULT_TEST_TARGET: prove + DEVELOPER: 1 + freebsd_instance: + image_family: freebsd-12-3 + memory: 2G + install_script: + pkg install -y gettext gmake perl5 + create_user_script: + - pw useradd git + - chown -R git:git . + build_script: + - su git -c gmake + test_script: + - su git -c 'gmake test' Thanks, ZheNing Hu
