`pipe` is a useful operator for creating pipelines of functions.
It works around the usual problem of e.g. string operations becoming
deeply nested functions.
In principle, there are four different ways this function could be
written:
pipe val [ f1 .. fn ]
pipe val [ fn .. f1 ]
compose [ f1 .. fn ] val
compose [ fn .. f1 ] val
The third and fourth form mirror composition of functions, they would
be the same as e.g. `(f1 << f2 << f3 .. << fn) val`.
However, it is not clear which direction the list should have (as one
can see in the second form, which is the most absurd.
In order not to confuse users, we decide for the most “intuitive”
form, which mirrors the way unix pipes work (thus the name `pipe`).
The flow of data goes from left to right.
Co-Authored-By: Silvan Mosberger <infinisil@icloud.com>
The main purpose is to bring attention to `flip map`, which improves
code readablity. It is useful when ad-hoc anonymous function
grows two or more lines in `map` application:
```
map (lcfg:
let port = lcfg.port;
portStr = if port != defaultPort then ":${toString port}" else "";
scheme = if cfg.enableSSL then "https" else "http";
in "${scheme}://cfg.hostName${portStr}"
) (getListen cfg);
```
Compare this to `foreach`-style:
```
foreach (getListen cfg) (lcfg:
let port = lcfg.port;
portStr = if port != defaultPort then ":${toString port}" else "";
scheme = if cfg.enableSSL then "https" else "http";
in "${scheme}://cfg.hostName${portStr}"
);
```
This is similar to Haskell's `for` (http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Traversable.html#v:for)
This commit changes the `mkAliasOptionModule` function to make sure that
the priority for the aliased option is propagated to the non-aliased
option.
This also affects the `mkRenamedOptionModule` function in a similar
fashion.
This also removes the `mkAliasOptionModuleWithPriority` function, since
its functionality is now subsumed by `mkAliasOptionModule`.
This change was recommended by @nbp:
https://github.com/NixOS/nixpkgs/pull/53397#discussion_r245487432
Fake hashes can be used as placeholders for all the places, where
Nix expression requires a hash, but we don't yet have one.
This should be more convenient than following:
- echo|sha256sum, copy into clipboard, go to editor, paste into previously
edited place
- search nixpkgs for a random package, copy it's hash to cliboard, go to
editor, paste into previously edited place
Nix can add support for these fake hashes. In that case printed error should contain
only 1 hash, so no more problem "which of two hashes from error should I use?"
Idea by irc:Synthetica
This commit adds a function `mkAliasOptionModuleWithPriority`. This
function will make an alias to an existing option and copy over the
priority.
This functionality is needed for PRs like #53041. In that case
`nixos-generate-config` added an option to `hardware-configuration.nix`
with `mkDefault`. That option was then changed and an alias created for
the old name.
The end user should be able to set the non-alias option in their
`configuration.nix` and have everything work correctly. Without this
function, the priority for the option won't be copied over correctly
and the end-user will get a message saying they have the same option
set to two different values.
Suppose I have a Gemfile like this:
source "https://rubygems.org"
gem "actioncable"
gem "websocket-driver", group: :test
The gemset.nix generated by Bundix 2.4.1 will set ActionCable's groups
to [ "default" ], and websocket-driver's to [ "test" ]. This means that
the generated bundlerEnv wouldn't include websocket-driver unless the
test group was included, even though it's required by the default group.
This is arguably a bug in Bundix (websocket-driver's groups should
probably be [ "default" "test" ] or just [ "default" ]), but there's no
reason bundlerEnv should omit dependencies even given such an input --
it won't necessarily come from Bundix, and it would be good for
bundlerEnv to do the right thing.
To fix this, filterGemset is now a recursive function, that adds
dependencies of gems in the group to the filtered gemset until it
stabilises on the gems that match the required groups, and all of their
recursive dependencies.
- moved function into strings.nix
- renamed function from makePerl5Lib
- removed duplicates entries in the resulting value
- rewrote the function from scratch after learning a few things (much cleaner now)
As suggested in https://github.com/NixOS/nixpkgs/pull/39416#discussion_r183845745
the versioning attributes in `lib` should be consistent to
`nixos/version` which implicates the following changes:
* `lib.trivial.version` -> `lib.trivial.release`
* `lib.trivial.suffix` -> `lib.trivial.versionSuffix`
* `lib.nixpkgsVersion` -> `lib.version`
As `lib.nixpkgsVersion` is referenced several times in `NixOS/nixpkgs`,
`NixOS/nix` and probably several user's setups. As the rename will cause
a notable impact it's better to keep `lib.nixpkgsVersion` as alias with
a warning yielded by `builtins.trace`.
This allows the lib fixed point to be extended with
myLib = lib.extend (self: super: {
foo = "foo";
})
With this it's possible to have the new modified lib attrset available to all
modules when using evalModules
myLib.evalModules {
modules = [ ({ lib, ... }: {
options.bar = lib.mkOption {
default = lib.foo;
};
}) ];
}
=> { config = { bar = "foo"; ... }; options = ...; }
First, we need check against the host platform, not the build platform.
That's simple enough.
Second, we move away from exahustive finite case analysis (i.e.
exhaustively listing all platforms the package builds on). That only
work in a closed-world setting, where we know all platforms we might
build one. But with cross compilation, we may be building for arbitrary
platforms, So we need fancier filters. This is the closed world to open
world change.
The solution is instead of having a list of systems (strings in the form
"foo-bar"), we have a list of of systems or "patterns", i.e. attributes
that partially match the output of the parsers in `lib.systems.parse`.
The "check meta" logic treats the systems strings as an exact whitelist
just as before, but treats the patterns as a fuzzy whitelist,
intersecting the actual `hostPlatform` with the pattern and then
checking for equality. (This is done using `matchAttrs`).
The default convenience lists for `meta.platforms` are now changed to be
lists of patterns (usually a single pattern) in
`lib/systems/for-meta.nix` for maximum flexibility under this new
system.
Fixes#30902
Based on a request by @oxij:
“Can we also rename this file to `maintainers/maintainers-list.nix` while we at
this? Motivation: much saner `git log ./lib`.”
Based on https://github.com/NixOS/nixpkgs/pull/34842, the
nix-instantiate output was pretty-printed and the validity of the github handles
manually verified, by automatically checking whether the user handles exist on
github (https://github.com/userhandle, status 200 or 404).
Each handle under 5 characters was manually checked (because the collision
probability with non-maintainer accounts is high), each missing entry was
manually researched.
The script used is kept in `maintainers/scripts` as an example of how to work
with the mainainers list through nix’ JSON interface.
Among other things, this will allow *2nix tools to output plain data
while still being composable with the traditional
callPackage/.override interfaces.
