f3feef687f
Summary:
`folly::format` is a problematic API because it returns a `Formatter` object that may store references to arguments as its comment warns:
```
* Formatter class.
*
* Note that this class is tricky, as it keeps *references* to its lvalue
* arguments (while it takes ownership of the temporaries), and it doesn't
* copy the passed-in format string. Thankfully, you can't use this
* directly, you have to use format(...) below.
```
This has negative safety and performance (encourages reuse of the same formatter) implications because contrary to what the comment says you can use the object directly since it's returned from `folly::format`. For example
```
auto f = folly::format(std::string("{}"), 42);
f.str();
```
is a UB with no compile-time diagnostic (only caught by ASAN).
It's also unnecessary because the `Formatter` object is usually converted to string straight away via `str()` or written to an output stream. Reusing the formatter doesn't make much sense either because the expensive part is formatting, not capturing arguments.
This diff deprecates `folly::format` suggesting `fmt::format` as a potential replacement. `fmt::format` doesn't have the above problem because arguments are always in scope. It also has the following advantages:
* Better compile times.
* Compile-time format string checks.
* Compatibility with C++20 `std::format`.
* Better performance, particularly with format string compilation which eliminates format string processing overhead altogether.
* Smaller binary footprint.
Also remove `folly::writeTo` which is no longer used and the `format_nested_fbstrings` benchmark which is identical to `format_nested_strings` since there is no `fbstr()` any more.
Reviewed By: yfeldblum
Differential Revision: D26391489
fbshipit-source-id: f0309e78db0eb6d8c22b426d4cc333a17c53f73e
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|---|---|---|
| .github/workflows | ||
| build | ||
| CMake | ||
| common | ||
| configerator/structs/scm/mononoke | ||
| eden | ||
| .gitignore | ||
| .projectid | ||
| .travis.yml | ||
| build.bat | ||
| build.sh | ||
| CMakeLists.txt | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| LICENSE | ||
| make-client.py | ||
| README.md | ||
| requirements_ubuntu.txt | ||
| rustfmt.toml | ||
EdenSCM
EdenSCM is a cross-platform, highly scalable source control management system.
It aims to provide both user-friendly and powerful interfaces for users, as well as extreme scalability to deal with repositories containing many millions of files and many millions of commits.
EdenSCM is comprised of three main components:
- The
edenCLI: The client-side command line interface for users to interact with EdenSCM. - Mononoke: The server-side part of EdenSCM.
- EdenFS: A virtual filesystem for efficiently checking out large repositories.
EdenSCM's scalability goals are to ensure that all source control operations scale with the number of files in use by a developer, and not with the size of the repository itself. This enables fast, performant developer experiences even in massive repositories with many long files and very long commit histories.
The eden CLI
The eden CLI was originally based on
Mercurial, and shares many aspects of the UI
and features of Mercurial.
The CLI code can be found in the eden/scm subdirectory.
Building the eden CLI
The eden CLI currently builds and runs on Linux, Mac, and Windows. The
setup.py script is the main interface for building the CLI.
Mononoke
Mononoke is the server-side component of EdenSCM.
Despite having originally evolved from Mercurial, EdenSCM is not a distributed source control system. In order to support massive repositories, not all repository data is downloaded to the client system when checking out a repository. Clients ideally only download the minimal amount of data necessary, and then fetch additional data from the server as it is needed.
Building Mononoke
The Mononoke code lives under eden/mononoke
Mononoke currently builds and runs only on Linux, and is not yet buildable
outside of Facebook's internal environment. Work is still in progress to
support building Mononoke with Rust's cargo build system.
EdenFS
EdenFS is a virtual file system for managing EdenSCM checkouts.
EdenFS speeds up operations in large repositories by only populating working
directory files on demand, as they are accessed. This makes operations like
checkout much faster, in exchange for a small performance hit when first
accessing new files. This is quite beneficial in large repositories where
developers often only work with a small subset of the repository at a time.
EdenFS has similar performance advantages to using sparse checkouts, but a much better user experience. Unlike with sparse checkouts, EdenFS does not require manually curating the list of files to check out, and users can transparently access any file without needing to update the profile.
EdenFS also keeps track of which files have been modified, allowing very
efficient status queries that do not need to scan the working directory.
The filesystem monitoring tool Watchman
also integrates with EdenFS, allowing it to more efficiently track updates to
the filesystem.
More detailed EdenFS design documentation can be found at eden/fs/docs/Overview.md.
Building EdenFS
EdenFS currently builds on Linux, Mac, and Windows.
The recommended way to build EdenFS is using the build.sh script in the
top-level of the repository. This script will download and build all of the
necessary dependencies for EdenFS, before building EdenFS itself. On Windows
use the build.bat script instead of build.sh.
This build script will create an output directory outside of the repository
where it will perform the build. You can control this output directory
location by passing a --scratch-path argument to the build script.
On Ubuntu, install the requirements in requirements_ubuntu.txt. You will
also need m4 and Rust installed.
Support
EdenSCM is the primary source control system used at Facebook, and is used for Facebook's main monorepo code base.
Support for using EdenSCM outside of Facebook is still highly experimental. While we would be interested to hear feedback if you run into issues, supporting external users is not currently a high priority for the development team, so we unfortunately cannot guarantee prompt support at this time.
License
See LICENSE.