# Using git-update-index to add existing tree objects at other paths 4 messages from 2022-10-04 to 2022-10-05. Participants: Sean Allred, Chris Torek, Phillip Wood, Junio C Hamano. Thread: https://gitlist.dev/t/58561 ## Sean Allred, 2022-10-04 13:44 Subject: Using git-update-index to add existing tree objects at other paths Message-ID: <87o7ur1wi9.fsf@gmail.com> URL: https://gitlist.dev/e/87o7ur1wi9.fsf%40gmail.com ``` Hi all, We're looking to create a tool that can duplicate a specific subtree elsewhere in the repository. (This is part of a rag-tag replacement for svn:external that will continue to work with our existing build infrastructure while we adjust everything to be organized better in the actual repository.) The basic idea is as follows: 1. At the repository root, there is a manifest that defines groups of paths that should be copies of one another. 2. Server hook logic will enforce that for each new commit, the paths in the manifest at that commit are TREESAME to each other. This guarantee is important for our build processes. 3. Client-side tooling will help produce this TREESAME-ness in the context of sparse-checkouts. Support for sparse-index may not be so large a concern as this entire approach is more of a stopgap measure. It's this last step, the client-side tooling, that is proving tricky. ### Solution based on git-fast-import A working solution using git-fast-import was recently submitted for review: $ cat | git fast-import feature done commit refs/heads/ committer (...) data < M 040000 TREEID1 PATH1 M 040000 TREEID1 PATH2 M 040000 TREEID1 PATH3 M 040000 TREEID2 PATH1 M 040000 TREEID2 PATH2 M 040000 TREEID2 PATH3 (...) done but using fast-import for this purpose seems like an abuse. It's especially suboptimal because it creates a *new* commit that brings everything into sync, so the two commits (the one the developer makes and the one created by this tooling) must be squashed together. ### Something better? This feels like a job for git-update-index. From the docs, > USING --INDEX-INFO > ------------------ > > `--index-info` is a more powerful mechanism that lets you feed > multiple entry definitions from the standard input, and designed > specifically for scripts. It can take inputs of three formats: > > . mode SP type SP sha1 TAB path > + > This format is to stuff `git ls-tree` output into the index. but the following does not work: $ cat | git update-index --index-info 040000 tree TREEID1 PATH1 (using the appropriate delimiters, of course). This command succeeds, but checking git-status (and confirming with other tools like `git ls-files -s`) reveal that this invocation did not have the desired effect: > (mode) (oid) (stage) (path) > (...) > 100755 (oid1) 0 PATH1FILENAME > 100755 (oid2) 0 PATH1FILENAME > 100755 (oid3) 0 PATH1FILENAME with `PATH1` simply prepended to each file in TREEID1. In contrast, the desired state is > 100755 (oid1) 0 PATH1/FILENAME > 100755 (oid2) 0 PATH1/FILENAME > 100755 (oid3) 0 PATH1/FILENAME I also tried appending a / at the end of PATH1 (this isn't ls-tree output, but it's 'reasonable'), but git-update-index simply ignores the line with the message > Ignoring path PATH1/ Is there a better, recommended way to do this? Given the language in git-update-index.txt, is this a bug / functionality gap in update-index? The documentation reads as if I could $ git ls-tree | git update-index --index-info but it seems that is not the case. Thanks, -Sean -- Sean Allred ``` ## Chris Torek, 2022-10-04 15:10 Subject: Re: Using git-update-index to add existing tree objects at other paths Message-ID: URL: https://gitlist.dev/e/CAPx1GvfsRipG0qgDmMMoU%2BWCWCEyr4ayJteYWAy%2BEoJOoaNQXg%40mail.gmail.com In-Reply-To: <87o7ur1wi9.fsf@gmail.com> ``` On Tue, Oct 4, 2022 at 7:43 AM Sean Allred wrote: > ... but the following does not work: > > $ cat | git update-index --index-info > 040000 tree TREEID1 PATH1 The index is not designed to hold tree objects (at least not at this level), and update-index should be fed only the full path names of files, symbolic links (mode 120000), or gitlinks (mode 160000). Whether it's reasonable to ask for the update-index command to understand that `040000 tree ` means to insert all the files *within* the given (existing) tree object, at the implied constructed paths, I'll leave as an open topic here. :-) But if you were to do this manually yourself, it should work. Chris ``` ## Phillip Wood, 2022-10-04 15:13 Subject: Re: Using git-update-index to add existing tree objects at other paths Message-ID: <25ec850e-8677-8011-912e-315efb93db4f@dunelm.org.uk> URL: https://gitlist.dev/e/25ec850e-8677-8011-912e-315efb93db4f%40dunelm.org.uk In-Reply-To: <87o7ur1wi9.fsf@gmail.com> ``` Hi Sean On 04/10/2022 14:44, Sean Allred wrote: > Hi all, > [...] >> USING --INDEX-INFO >> ------------------ >> >> `--index-info` is a more powerful mechanism that lets you feed >> multiple entry definitions from the standard input, and designed >> specifically for scripts. It can take inputs of three formats: >> >> . mode SP type SP sha1 TAB path >> + >> This format is to stuff `git ls-tree` output into the index. > > but the following does not work: > > $ cat | git update-index --index-info > 040000 tree TREEID1 PATH1 > > (using the appropriate delimiters, of course). This command succeeds, > but checking git-status (and confirming with other tools like `git > ls-files -s`) reveal that this invocation did not have the desired > effect: > >> (mode) (oid) (stage) (path) >> (...) >> 100755 (oid1) 0 PATH1FILENAME >> 100755 (oid2) 0 PATH1FILENAME >> 100755 (oid3) 0 PATH1FILENAME > > with `PATH1` simply prepended to each file in TREEID1. In contrast, the > desired state is > >> 100755 (oid1) 0 PATH1/FILENAME >> 100755 (oid2) 0 PATH1/FILENAME >> 100755 (oid3) 0 PATH1/FILENAME > > I also tried appending a / at the end of PATH1 (this isn't ls-tree > output, but it's 'reasonable'), but git-update-index simply ignores the > line with the message > >> Ignoring path PATH1/ > > Is there a better, recommended way to do this? Given the language in > git-update-index.txt, is this a bug / functionality gap in update-index? > The documentation reads as if I could > > $ git ls-tree | git update-index --index-info I agree update-index sounds like the right tool for what you want to do and this sounds like a bug but I'm not that familiar with update-index. As a workaround you could try git ls-tree -r arg | sed s: : new/prefix/: | git update-index --index-info Best Wishes Phillip ``` ## Junio C Hamano, 2022-10-05 19:39 Subject: Re: Using git-update-index to add existing tree objects at other paths Message-ID: URL: https://gitlist.dev/e/xmqq8rluoy9r.fsf%40gitster.g In-Reply-To: ``` Chris Torek writes: > On Tue, Oct 4, 2022 at 7:43 AM Sean Allred wrote: >> ... but the following does not work: >> >> $ cat | git update-index --index-info >> 040000 tree TREEID1 PATH1 > > The index is not designed to hold tree objects (at least not at this level), > and update-index should be fed only the full path names of files, symbolic > links (mode 120000), or gitlinks (mode 160000). Correct. With the ongoing "sparse-index" work, it may not be an entirely unreasonable idea to extend the "update-index" command to allow it adding a tree entry there (after removing the entries that are for anything that fall inside that directory), but we are not there yet, in the sense that we haven't even discussed if doing it at this level is a reasonable thing to do. ```