160f2dabed
Aside from adding comments to document the logic in `Cache.Manifest.hit` better, this commit fixes two serious bugs. The first, spotted by Andrew, is that when upgrading from a shared to an exclusive lock on the manifest file, we do not seek it back to the start. This is a simple fix. The second is more subtle, and has to do with the computation of file digests. Broadly speaking, the goal of the main loop in `hit` is to iterate the files listed in the manifest file, and check if they've changed, based on stat and a file hash. While doing this, the `bin_digest` field of `std.Build.Cache.File`, which is initially `undefined`, is populated for all files, either straight from the manifest (if the stat matches) or recomputed from the file on-disk. This file digest is then used to update `man.hash.hasher`, which is building the final hash used as, for instance, the output directory name when the compiler emits into the cache directory. When `hit` returns a cache miss, it is expected that `man.hash.hasher` includes the digests of all "initial files"; that is, those which have been already added with e.g. `addFilePath`, but not those which will later be added with `addFilePost` (even though the manifest file has told us about some such files). Previously, `hit` was using the `unhit` function to do this in a few cases. However, this is incorrect, because `hit` assumes that all files already have their `bin_digest` field populated; this function is only valid to call *after* `hit` returns. Instead, we need to actually compute the hashes which haven't yet been populated. Even if this logic has been working, there was still a bug here, because we called `unhit` when upgrading from a shared to an exclusive lock, writing the (potentially `undefined`) file digests, but the loop itself writes the file digests *again*! All in all, the hashing logic here was actually incredibly broken. I've taken the opportunity to restructure this section of the code into what I think is a more readable format. A new function, `hitWithCurrentLock`, uses the open manifest file to try and find a cache hit. It returns a tagged union which, in the miss case, tells the caller (`hit`) how many files already have their hash populated. This avoids redundant work recomputing the same hash multiple times in situations where the lock needs upgrading. This also eliminates the outer loop from `hit`, which was a little confusing because it iterated no more than twice! The bugs fixed here could manifest in several different ways depending on how contended file locks were satisfied. Most notably, on a cache miss, the Zig compiler might have written the compilation output to the incorrect directory (because it incorrectly constructed a hash using `undefined` or repeated file digests), resulting in all future hits on this manifest causing `error.FileNotFound`. This is #23110. I have been able to reproduce #23110 on `master`, and have not been able to after this commit, so I am relatively sure this commit resolves that issue. Resolves: #23110 |
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| .github | ||
| ci | ||
| cmake | ||
| doc | ||
| lib | ||
| src | ||
| stage1 | ||
| test | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| bootstrap.c | ||
| build.zig | ||
| build.zig.zon | ||
| CMakeLists.txt | ||
| LICENSE | ||
| README.md | ||
A general-purpose programming language and toolchain for maintaining robust, optimal, and reusable software.
Documentation
If you are looking at this README file in a source tree, please refer to the Release Notes, Language Reference, or Standard Library Documentation corresponding to the version of Zig that you are using by following the appropriate link on the download page.
Otherwise, you're looking at a release of Zig, so you can find the language
reference at doc/langref.html, and the standard library documentation by
running zig std, which will open a browser tab.
Installation
A Zig installation is composed of two things:
- The Zig executable
- The lib/ directory
At runtime, the executable searches up the file system for the lib/ directory, relative to itself:
- lib/
- lib/zig/
- ../lib/
- ../lib/zig/
- (and so on)
In other words, you can unpack a release of Zig anywhere, and then begin
using it immediately. There is no need to install it globally, although this
mechanism supports that use case too (i.e. /usr/bin/zig and /usr/lib/zig/).
Building from Source
Ensure you have the required dependencies:
- CMake >= 3.15
- System C/C++ Toolchain
- LLVM, Clang, LLD development libraries == 19.x
Then it is the standard CMake build process:
mkdir build
cd build
cmake ..
make install
For more options, tips, and troubleshooting, please see the Building Zig From Source page on the wiki.
Building from Source without LLVM
In this case, the only system dependency is a C compiler.
cc -o bootstrap bootstrap.c
./bootstrap
This produces a zig2 executable in the current working directory. This is a
"stage2" build of the compiler,
without LLVM extensions, and is
therefore lacking these features:
- Release mode optimizations
- aarch64 machine code backend
- @cImport
- zig translate-c
- Ability to compile assembly files
- Some ELF linking features
- Most COFF/PE linking features
- Some WebAssembly linking features
- Ability to create import libs from def files
- Ability to create static archives from object files
- Ability to compile C, C++, Objective-C, and Objective-C++ files
However, a compiler built this way does provide a C backend, which may be useful for creating system packages of Zig projects using the system C toolchain. In this case, LLVM is not needed!
Furthermore, a compiler built this way provides an LLVM backend that produces bitcode files, which may be compiled into object files via a system Clang package. This can be used to produce system packages of Zig applications without the Zig package dependency on LLVM.
Contributing
Zig is Free and Open Source Software. We welcome bug reports and patches from everyone. However, keep in mind that Zig governance is BDFN (Benevolent Dictator For Now) which means that Andrew Kelley has final say on the design and implementation of everything.
One of the best ways you can contribute to Zig is to start using it for an open-source personal project.
This leads to discovering bugs and helps flesh out use cases, which lead to further design iterations of Zig. Importantly, each issue found this way comes with real world motivations, making it straightforward to explain the reasoning behind proposals and feature requests.
You will be taken much more seriously on the issue tracker if you have a personal project that uses Zig.
The issue label Contributor Friendly exists to help you find issues that are limited in scope and/or knowledge of Zig internals.
Please note that issues labeled Proposal but do not also have the Accepted label are still under consideration, and efforts to implement such a proposal have a high risk of being wasted. If you are interested in a proposal which is still under consideration, please express your interest in the issue tracker, providing extra insights and considerations that others have not yet expressed. The most highly regarded argument in such a discussion is a real world use case.
For more tips, please see the Contributing page on the wiki.
Community
The Zig community is decentralized. Anyone is free to start and maintain their own space for Zig users to gather. There is no concept of "official" or "unofficial". Each gathering place has its own moderators and rules. Users are encouraged to be aware of the social structures of the spaces they inhabit, and work purposefully to facilitate spaces that align with their values.
Please see the Community wiki page for a public listing of social spaces.