tl;dr: This series contributes the Scalar command to the Git project. This command provides an opinionated way to create and configure repositories with a focus on very large repositories. Background ========== Years ago, Microsoft wanted to move the source code of the Windows operating system to Git. The challenge there was to prove that Git could scale to massive monorepos. The VFS for Git (formerly GVFS) project was born to take up that challenge. The final solution included a virtual filesystem (with both user-mode and kernel components) and a customized fork of Git for Windows. This solution contained several key concepts, such as only populating a portion of the working directory, demand-fetching blobs, and performing periodic repo maintenance in the background. However, the required kernel drivers made it difficult to port the solution to other platforms. But it was realized that many of these key concepts were independent of the actual VFS and its projection of the working directory. The Scalar project was created to make that separation, refine the key concepts, and then extract those features into the new Scalar command. The present =========== The Scalar project provides a completely functional non-virtual experience for monorepos. But why stop there. The Scalar project was designed to be a self-destructing vehicle to allow those key concepts to be moved into core Git itself for the benefit of all. For example, partial clone, sparse-checkout, and background maintenance have already been upstreamed and removed from Scalar proper. This patch series provides a C-based implementation of the final remaining portions of the Scalar command. This will make it easier for users to experiment with the Scalar command. It will also make it substantially easier to experiment with moving functionality from Scalar into core Git, while maintaining backwards-compatibility for existing Scalar users. The C-based Scalar has been shipped to Scalar users, and can be tested by any interested reader: https://github.com/microsoft/git/releases/tag/v2.33.0.vfs.0.0 (it offers a Git for Windows installer, a macOS package and an Ubuntu package). Opportunities ============= Apart from providing the Scalar command, this contribution is intended to serve as a basis for further mailing list discussions on moving (some of) these key concepts into the main Git commands. For example, we previously discussed the idea of a "git big-clone" that does much of what "scalar clone" is doing. This patch series is a step to make such functionality exist in the Git code base while we simmer on what such a "git big-clone" command-line interface would look like. This is one of many possible ways to do this. Creating a 'git big-clone' could lock Git into backwards compatibility concerns so it is necessary to approach such an endeavor with caution. As a discussion starter, the scalar clone <url> command does roughly this: 1. git clone --sparse --filter=blob:none /src 2. git -C /src sparse-checkout init --cone 3. git -C /src config (many times) 4. git -C /src maintenance start It is my hope inspire discussions about what parts of Scalar could go into core Git, and where, and in which form. While we wish to maintain backwards-compatibility of Scalar's command-line interface (because it is already in use), by having the Scalar code in the same code base as Git's, it will be much easier to move functionality without having to maintain loose version coupling between independently-versioned Scalar and Git. The tight version-coupling, along with having access to libgit.a also allows the C-based implementation of Scalar to be much smaller than the original .NET version. For example, we might choose in the future to implement, say, git clone --scale=partial,cone to initialize a partial clone with a cone-sparse checkout, that would not only be totally doable, and not only would we already have precedent and data to prove that this actually makes engineers happy who have to work on ginormous repositories, but we could then also implement it by moving parts of contrib/scalar/ to builtin/ (where contrib/scalar/ would then call the built-ins accordingly rather than hard-coding the defaults itself). We now also have the opportunity to discuss the merits of Scalar's clone caching, which is not actually part of this patch series because it is a bit coupled with the GVFS parts of microsoft/git for the moment, where clones automatically get registered with a populated alternate repository that is identified by the URL, meaning: subsequent clones of the same repository are vastly faster than the first one because they do not actually download the already-received objects again, they access the cache instead. Another thing that I could imagine to be discussed at length is the distinction between enlistment and worktree (where the latter is the actual Git worktree and usually lives in the src/ subdirectory of the former). This encourages untracked and ignored files to be placed outside the worktree, making Git's job much easier. This idea, too, might find its way in one way or another into Git proper. These are just a few concepts in Scalar that do not yet have equivalents in Git. By putting this initial implementation into contrib/, we create a foundation for future discussions of these concepts. We plan on updating the recommended config settings in scalar register as new Git features are available (such as builtin FSMonitor and sparse-index, when ready). To facilitate upgrading existing Scalar enlistments, their paths are automatically added to the [scalar] section of the global Git config, and the scalar reconfigure --all command will process all of them. Epilogue ======== Now, to address some questions that I imagine every reader has who made it this far: * Why not put the Scalar functionality directly into a built-in? Creating a Git builtin requires scrutiny over every aspect of the feature, which is difficult to do while also maintaining the command-line interface contract and expected behavior of the Scalar command (there are existing users, after all). By having the Scalar command in contrib/, we present a simple option for users to have these features in the short term while the Git contributor community decides which bits to absorb into Git built-ins. * Why implement the Scalar command in the Git codebase? We ported Scalar to the microsoft/git fork for several reasons. First, we realized it was possible now that the core features exist inside Git itself. Second, compiling Scalar directly within a version of Git allows us to remove a version compatibility check from each config option that might or might not apply based on the installed Git version. Finally, this new location has greatly simplified our release process and the installation process for users. We now have ways to install Scalar with microsoft/git via winget, brew, and apt-get. This has been the case since we shipped v2.32.0 to our users, read: this setup has served us well already. * Why contribute Scalar to the Git project? We are biased, of course, yet we do have evidence that the Scalar command is a helpful tool that offers an simple way to handle huge repositories with ease. By contributing it to the core Git project, we are able to share it with more users, especially some users who do not want to install the microsoft/git fork. We intend to include Scalar as a component in git-for-windows/git, but are contributing it here first. Further, we think there is benefit to the Git developer community as this presents an example of how to set certain defaults that work for large repositories. * Does this integrate with the built-in FSMonitor yet? No, not yet. I do have a couple of add-on patch series lined up, one of them being the integration with the built-in FSMonitor, which obviously has to wait until the FSMonitor patch series advances further. Changes since v1: * A couple typos were fixed * The code parsing the output of ls-remote was made more readable * The indentation used in scalar.txt now consistently uses tabs * We no longer hard-code core.bare = false when registering with Scalar Derrick Stolee (4): scalar: 'register' sets recommended config and starts maintenance scalar: 'unregister' stops background maintenance scalar: implement 'scalar list' scalar: implement the `run` command Johannes Schindelin (10): scalar: create a rudimentary executable scalar: start documenting the command scalar: create test infrastructure scalar: let 'unregister' handle a deleted enlistment directory gracefully scalar: implement the `clone` subcommand scalar: teach 'clone' to support the --single-branch option scalar: allow reconfiguring an existing enlistment scalar: teach 'reconfigure' to optionally handle all registered enlistments scalar: implement the `version` command scalar: accept -C and -c options before the subcommand Matthew John Cheetham (1): scalar: implement the `delete` command Makefile | 8 + contrib/scalar/.gitignore | 5 + contrib/scalar/Makefile | 57 +++ contrib/scalar/scalar.c | 844 +++++++++++++++++++++++++++++++ contrib/scalar/scalar.txt | 156 ++++++ contrib/scalar/t/Makefile | 78 +++ contrib/scalar/t/t9099-scalar.sh | 88 ++++ 7 files changed, 1236 insertions(+) create mode 100644 contrib/scalar/.gitignore create mode 100644 contrib/scalar/Makefile create mode 100644 contrib/scalar/scalar.c create mode 100644 contrib/scalar/scalar.txt create mode 100644 contrib/scalar/t/Makefile create mode 100755 contrib/scalar/t/t9099-scalar.sh base-commit: ebf3c04b262aa27fbb97f8a0156c2347fecafafb Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1005%2Fdscho%2Fscalar-the-beginning-v2 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1005/dscho/scalar-the-beginning-v2 Pull-Request: https://github.com/gitgitgadget/git/pull/1005 Range-diff vs v1: 1: b8c7d3f8450 = 1: b8c7d3f8450 scalar: create a rudimentary executable 2: 4f886575dcf = 2: 4f886575dcf scalar: start documenting the command 3: bcfde9bc765 = 3: bcfde9bc765 scalar: create test infrastructure 4: 3786f4c597f ! 4: ee3e26a0c4e scalar: 'register' sets recommended config and starts maintenance @@ contrib/scalar/scalar.c + */ + { "core.untrackedCache", "false" }, +#endif -+ { "core.bare", "false" }, + { "core.logAllRefUpdates", "true" }, + { "credential.https://dev.azure.com.useHttpPath";, "true" }, + { "credential.validate", "false" }, /* GCM4W-only */ @@ contrib/scalar/scalar.txt: will be identical to the worktree. +~~~~~~~~ + +register [<enlistment>]:: -+ Adds the enlistment's repository to the list of registered repositories -+ and starts background maintenance. If `<enlistment>` is not provided, -+ then the enlistment associated with the current working directory is -+ registered. ++ Adds the enlistment's repository to the list of registered repositories ++ and starts background maintenance. If `<enlistment>` is not provided, ++ then the enlistment associated with the current working directory is ++ registered. +++ ++Note: when this subcommand is called in a worktree that is called `src/`, its ++parent directory is considered to be the Scalar enlistment. If the worktree is ++_not_ called `src/`, it itself will be considered to be the Scalar enlistment. + SEE ALSO -------- 5: 2a6ac170e6b ! 5: 6142f75875b scalar: 'unregister' stops background maintenance @@ contrib/scalar/scalar.txt: SYNOPSIS DESCRIPTION ----------- -@@ contrib/scalar/scalar.txt: register [<enlistment>]:: - then the enlistment associated with the current working directory is - registered. +@@ contrib/scalar/scalar.txt: Note: when this subcommand is called in a worktree that is called `src/`, its + parent directory is considered to be the Scalar enlistment. If the worktree is + _not_ called `src/`, it itself will be considered to be the Scalar enlistment. +Unregister +~~~~~~~~~~ + +unregister [<enlistment>]:: -+ Remove the specified repository from the list of repositories -+ registered with Scalar and stop the scheduled background maintenance. ++ Remove the specified repository from the list of repositories ++ registered with Scalar and stop the scheduled background maintenance. + SEE ALSO -------- 6: 087fc9be194 = 6: 82dd253154f scalar: let 'unregister' handle a deleted enlistment directory gracefully 7: c272ff4069d ! 7: fb7c931ddb3 scalar: implement 'scalar list' @@ contrib/scalar/scalar.txt: an existing Git worktree with Scalar whose name is no +~~~~ + +list:: -+ To see which repositories are currently registered by the service, run -+ `scalar list`. This subcommand does not need to be run inside a Scalar -+ enlistment. ++ To see which repositories are currently registered by the service, run ++ `scalar list`. This subcommand does not need to be run inside a Scalar ++ enlistment. + Register ~~~~~~~~ 8: 2cbf0b61113 ! 8: f3223c10788 scalar: implement the `clone` subcommand @@ Commit message experience and experiments of the Microsoft Windows and the Microsoft Office development teams. - Note: We intentionally use a slightly wasteful `set_config()` function - (which does not reuse a single `strbuf`, for example, though performance - _really_ does not matter here) for convenience and readability. - - Also note: since the `scalar clone` command is by far the most commonly + Note: since the `scalar clone` command is by far the most commonly called `scalar` subcommand, we document it at the top of the manual page. @@ contrib/scalar/scalar.c: static int unregister_dir(void) + + cp.git_cmd = 1; + strvec_pushl(&cp.args, "ls-remote", "--symref", url, "HEAD", NULL); -+ strbuf_addstr(&out, "-\n"); + if (!pipe_command(&cp, NULL, 0, &out, 0, NULL, 0)) { -+ char *ref = out.buf; -+ -+ while ((ref = strstr(ref + 1, "\nref: "))) { -+ const char *p; -+ char *head, *branch; ++ const char *line = out.buf; + -+ ref += strlen("\nref: "); -+ head = strstr(ref, "\tHEAD"); ++ while (*line) { ++ const char *eol = strchrnul(line, '\n'), *p; ++ size_t len = eol - line; ++ char *branch; + -+ if (!head || memchr(ref, '\n', head - ref)) ++ if (!skip_prefix(line, "ref: ", &p) || ++ !strip_suffix_mem(line, &len, "\tHEAD")) { ++ line = eol + (*eol == '\n'); + continue; ++ } + -+ if (skip_prefix(ref, "refs/heads/", &p)) { -+ branch = xstrndup(p, head - p); ++ eol = line + len; ++ if (skip_prefix(p, "refs/heads/", &p)) { ++ branch = xstrndup(p, eol - p); + strbuf_release(&out); + return branch; + } + + error(_("remote HEAD is not a branch: '%.*s'"), -+ (int)(head - ref), ref); ++ (int)(eol - p), p); + strbuf_release(&out); + return NULL; + } @@ contrib/scalar/scalar.txt: an existing Git worktree with Scalar whose name is no +~~~~~ + +clone [<options>] <url> [<enlistment>]:: -+ Clones the specified repository, similar to linkgit:git-clone[1]. By -+ default, only commit and tree objects are cloned. Once finished, the -+ worktree is located at `<enlistment>/src`. ++ Clones the specified repository, similar to linkgit:git-clone[1]. By ++ default, only commit and tree objects are cloned. Once finished, the ++ worktree is located at `<enlistment>/src`. ++ +The sparse-checkout feature is enabled (except when run with `--full-clone`) +and the only files present are those in the top-level directory. Use @@ contrib/scalar/scalar.txt: an existing Git worktree with Scalar whose name is no + +-b <name>:: +--branch <name>:: -+ Instead of checking out the branch pointed to by the cloned repository's -+ HEAD, check out the `<name>` branch instead. ++ Instead of checking out the branch pointed to by the cloned ++ repository's HEAD, check out the `<name>` branch instead. + +--[no-]full-clone:: -+ A sparse-checkout is initialized by default. This behavior can be turned -+ off via `--full-clone`. ++ A sparse-checkout is initialized by default. This behavior can be ++ turned off via `--full-clone`. + List ~~~~ list:: - To see which repositories are currently registered by the service, run -- `scalar list`. This subcommand does not need to be run inside a Scalar -- enlistment. -+ `scalar list`. This subcommand, like `clone`, does not need to be run -+ inside a Scalar enlistment. + To see which repositories are currently registered by the service, run +- `scalar list`. This subcommand does not need to be run inside a Scalar +- enlistment. ++ `scalar list`. This subcommand, like `clone`, does not need to be run ++ inside a Scalar enlistment. Register ~~~~~~~~ 9: 9af1c37c2ea ! 9: b3c4b3dccc6 scalar: teach 'clone' to support the --single-branch option @@ contrib/scalar/scalar.txt: scalar - an opinionated repository management tool scalar register [<enlistment>] scalar unregister [<enlistment>] @@ contrib/scalar/scalar.txt: subdirectories outside your sparse-checkout by using `git ls-tree HEAD`. - Instead of checking out the branch pointed to by the cloned repository's - HEAD, check out the `<name>` branch instead. + Instead of checking out the branch pointed to by the cloned + repository's HEAD, check out the `<name>` branch instead. +--[no-]single-branch:: -+ Clone only the history leading to the tip of a single branch, -+ either specified by the `--branch` option or the primary -+ branch remote's `HEAD` points at. ++ Clone only the history leading to the tip of a single branch, either ++ specified by the `--branch` option or the primary branch remote's ++ `HEAD` points at. ++ +Further fetches into the resulting repository will only update the +remote-tracking branch for the branch this option was used for the initial @@ contrib/scalar/scalar.txt: subdirectories outside your sparse-checkout by using +`--single-branch` clone was made, no remote-tracking branch is created. + --[no-]full-clone:: - A sparse-checkout is initialized by default. This behavior can be turned - off via `--full-clone`. + A sparse-checkout is initialized by default. This behavior can be + turned off via `--full-clone`. ## contrib/scalar/t/t9099-scalar.sh ## @@ contrib/scalar/t/t9099-scalar.sh: test_expect_success 'set up repository to clone' ' 10: c3f16bccd02 ! 10: b7fc2dc29c8 scalar: implement the `run` command @@ contrib/scalar/scalar.txt: scalar clone [--single-branch] [--branch <main-branch DESCRIPTION ----------- @@ contrib/scalar/scalar.txt: unregister [<enlistment>]:: - Remove the specified repository from the list of repositories - registered with Scalar and stop the scheduled background maintenance. + Remove the specified repository from the list of repositories + registered with Scalar and stop the scheduled background maintenance. +Run +~~~ + +scalar run ( all | config | commit-graph | fetch | loose-objects | pack-files ) [<enlistment>]:: -+ Run the given maintenance task (or all tasks, if `all` was specified). -+ Except for `all` and `config`, this subcommand simply hands off to -+ linkgit:git-maintenance[1] (mapping `fetch` to `prefetch` and -+ `pack-files` to `incremental-repack`). ++ Run the given maintenance task (or all tasks, if `all` was specified). ++ Except for `all` and `config`, this subcommand simply hands off to ++ linkgit:git-maintenance[1] (mapping `fetch` to `prefetch` and ++ `pack-files` to `incremental-repack`). ++ +These tasks are run automatically as part of the scheduled maintenance, +as soon as the repository is registered with Scalar. It should therefore 11: 13056f02018 ! 11: 9a834c23d08 scalar: allow reconfiguring an existing enlistment @@ contrib/scalar/scalar.c: static int set_recommended_config(void) - { "core.untrackedCache", "false" }, + { "core.untrackedCache", "false", 1 }, #endif -- { "core.bare", "false" }, - { "core.logAllRefUpdates", "true" }, - { "credential.https://dev.azure.com.useHttpPath";, "true" }, - { "credential.validate", "false" }, /* GCM4W-only */ @@ contrib/scalar/scalar.c: static int set_recommended_config(void) - { "feature.experimental", "false" }, - { "fetch.unpackLimit", "1" }, - { "fetch.writeCommitGraph", "false" }, -+ { "core.bare", "false", 1 }, + { "core.logAllRefUpdates", "true", 1 }, + { "credential.https://dev.azure.com.useHttpPath";, "true", 1 }, + { "credential.validate", "false", 1 }, /* GCM4W-only */ 12: 732a28c22fc ! 12: 79e9f5d203a scalar: teach 'reconfigure' to optionally handle all registered enlistments @@ contrib/scalar/scalar.txt: After a Scalar upgrade, or when the configuration of reconfigure the enlistment. +With the `--all` option, all enlistments currently registered with Scalar -+will be reconfigured. This option is meant to to be run every time Scalar -+was upgraded. ++will be reconfigured. This option is meant to to be run every time after ++Scalar is upgraded. + SEE ALSO -------- 13: 13afbd68812 ! 13: 94a21982652 scalar: implement the `delete` command @@ contrib/scalar/scalar.txt: scalar register [<enlistment>] DESCRIPTION ----------- @@ contrib/scalar/scalar.txt: With the `--all` option, all enlistments currently registered with Scalar - will be reconfigured. This option is meant to to be run every time Scalar - was upgraded. + will be reconfigured. This option is meant to to be run every time after + Scalar is upgraded. +Delete +~~~~~~ + +delete <enlistment>:: -+ This subcommand lets you delete an existing Scalar enlistment from your -+ local file system, unregistering the repository. ++ This subcommand lets you delete an existing Scalar enlistment from your ++ local file system, unregistering the repository. + SEE ALSO -------- 14: 73d08c0c894 ! 14: 707d8e19683 scalar: implement the `version` command @@ Commit message Since Scalar is now tightly coupled with Git, it does not make sense for them to show different versions. Therefore, it shows the same output as - `git versions`. For backwards-compatibility with the .NET version, + `git version`. For backwards-compatibility with the .NET version, `scalar version` prints to `stderr`, though (`git version` prints to `stdout` instead). 15: 6455b18f1b6 ! 15: 26e23b5c5e5 scalar: accept -C and -c options before the subcommand @@ contrib/scalar/scalar.txt: The `scalar` command implements various subcommands, +The following options can be specified _before_ the subcommand: + +-C <directory>:: -+ Before running the subcommand, change the working directory. This -+ option imitates the same option of linkgit:git[1]. ++ Before running the subcommand, change the working directory. This ++ option imitates the same option of linkgit:git[1]. + +-c <key>=<value>:: -+ For the duration of running the specified subcommand, configure this -+ setting. This option imitates the same option of linkgit:git[1]. ++ For the duration of running the specified subcommand, configure this ++ setting. This option imitates the same option of linkgit:git[1]. + COMMANDS -------- -- gitgitgadget
