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Thomas Watson 8fb885a19e qt{5,6}: disable QML disk cache by default 
Qt QML is a language for designing user interfaces. QML (and related
JavaScript) source files are compiled into bytecode at runtime before
execution. To save time, this bytecode is cached on disk.

The cache is keyed primarily off the application name and mtime of the
source file. Since application names rarely change, source files that
have passed through the store have their mtimes fixed at 1, and
SOURCE_DATE_EPOCH is also set to 1 during builds, compiled bytecode in
this cache for Qt programs built by Nix is rarely or never invalidated.

This results in programs running with QML bytecode that does not match
their source code, which manifests as a constant source of random and
unreproducible glitches, oddities, and crashes in Qt applications when
they are upgraded. For applications like SDDM and Plasma, the user may
be left with a completely broken system, and sometimes even rolling back
doesn't fix the issue.

This patch resolves the issue by simply patching Qt's QML module in all
supported versions to disable the disk cache by default as if the
environment variable QML_DISABLE_DISK_CACHE were always 1. Patching the
code ensures consistent behavior for all Qt applications in all
environments, including non-NixOS uses.

Simple benchmarking suggests an approximate 10% CPU time penalty when
launching QML-heavy applications, and no measurable penalty to booting
into Plasma. This is considerably more benign than the earlier behavior.

For testing or the performance conscious, use of the cache can be
re-enabled after understanding the risks by setting the environment
variable QML_FORCE_DISK_CACHE to 1. This can be done system-wide using
e.g. the `environment.sessionVariables` NixOS option.

Future work could change the cache key through source code changes or
automatic generation of an appropriate SOURCE_DATE_EPOCH. Until then,
this is a simple change which removes a large class of user frustration
and headache for little penalty.
2022-10-20 22:15:04 -05:00
.github .github/workflows: replace deprecated set-output 2022-10-16 07:41:12 +10:00
doc doc/stdenv: Move Other hooks after all hooks 2022-10-13 21:15:19 +02:00
lib Merge master into staging-next 2022-10-21 00:05:50 +00:00
maintainers Merge pull request #196149 from mktip/circumflex 2022-10-19 23:26:32 +02:00
nixos Merge master into staging-next 2022-10-21 00:05:50 +00:00
pkgs qt{5,6}: disable QML disk cache by default 2022-10-20 22:15:04 -05:00
.editorconfig .editorconfig: disable for Apple nib files 2022-08-17 22:06:57 +09:00
.git-blame-ignore-revs git-blame-ignore-revs: fix commit hash 2022-08-25 12:13:09 +02:00
.gitattributes
.gitignore .gitignore: add result ignore, accept python module 2022-09-16 14:20:15 -04:00
.mailmap init .mailmap 2022-09-23 14:00:09 +00:00
.version 22.11 is Raccoon 2022-05-23 20:08:07 +02:00
CONTRIBUTING.md Merge #175352: CONTRIBUTING.md: simplify rebasing instructions 2022-08-15 12:53:30 +02:00
COPYING
default.nix
flake.nix flake.nix: Format 2022-07-10 13:35:54 +02:00
README.md README: 21.11 -> 22.05 2022-05-31 08:36:12 +02:00

README.md

NixOS logo NixOS logo

Contributors badge Open Collective supporters

Nixpkgs is a collection of over 80,000 software packages that can be installed with the Nix package manager. It also implements NixOS, a purely-functional Linux distribution.

Manuals

  • NixOS Manual - how to install, configure, and maintain a purely-functional Linux distribution
  • Nixpkgs Manual - contributing to Nixpkgs and using programming-language-specific Nix expressions
  • Nix Package Manager Manual - how to write Nix expressions (programs), and how to use Nix command line tools

Community

Other Project Repositories

The sources of all official Nix-related projects are in the NixOS organization on GitHub. Here are some of the main ones:

  • Nix - the purely functional package manager
  • NixOps - the tool to remotely deploy NixOS machines
  • nixos-hardware - NixOS profiles to optimize settings for different hardware
  • Nix RFCs - the formal process for making substantial changes to the community
  • NixOS homepage - the NixOS.org website
  • hydra - our continuous integration system
  • NixOS Artwork - NixOS artwork

Continuous Integration and Distribution

Nixpkgs and NixOS are built and tested by our continuous integration system, Hydra.

Artifacts successfully built with Hydra are published to cache at https://cache.nixos.org/. When successful build and test criteria are met, the Nixpkgs expressions are distributed via Nix channels.

Contributing

Nixpkgs is among the most active projects on GitHub. While thousands of open issues and pull requests might seem a lot at first, it helps consider it in the context of the scope of the project. Nixpkgs describes how to build tens of thousands of pieces of software and implements a Linux distribution. The GitHub Insights page gives a sense of the project activity.

Community contributions are always welcome through GitHub Issues and Pull Requests. When pull requests are made, our tooling automation bot, OfBorg will perform various checks to help ensure expression quality.

The Nixpkgs maintainers are people who have assigned themselves to maintain specific individual packages. We encourage people who care about a package to assign themselves as a maintainer. When a pull request is made against a package, OfBorg will notify the appropriate maintainer(s). The Nixpkgs committers are people who have been given permission to merge.

Most contributions are based on and merged into these branches:

  • master is the main branch where all small contributions go
  • staging is branched from master, changes that have a big impact on Hydra builds go to this branch
  • staging-next is branched from staging and only fixes to stabilize and security fixes with a big impact on Hydra builds should be contributed to this branch. This branch is merged into master when deemed of sufficiently high quality

For more information about contributing to the project, please visit the contributing page.

Donations

The infrastructure for NixOS and related projects is maintained by a nonprofit organization, the NixOS Foundation. To ensure the continuity and expansion of the NixOS infrastructure, we are looking for donations to our organization.

You can donate to the NixOS foundation through SEPA bank transfers or by using Open Collective:

License

Nixpkgs is licensed under the MIT License.

Note: MIT license does not apply to the packages built by Nixpkgs, merely to the files in this repository (the Nix expressions, build scripts, NixOS modules, etc.). It also might not apply to patches included in Nixpkgs, which may be derivative works of the packages to which they apply. The aforementioned artifacts are all covered by the licenses of the respective packages.