This patch add a new argument to Nixpkgs default expression named "overlays".
By default, the value of the argument is either taken from the environment variable `NIXPKGS_OVERLAYS`,
or from the directory `~/.nixpkgs/overlays/`. If the environment variable does not name a valid directory
then this mechanism would fallback on the home directory. If the home directory does not exists it will
fallback on an empty list of overlays.
The overlays directory should contain the list of extra Nixpkgs stages which would be used to extend the
content of Nixpkgs, with additional set of packages. The overlays, i-e directory, files, symbolic links
are used in alphabetical order.
The simplest overlay which extends Nixpkgs with nothing looks like:
```nix
self: super: {
}
```
More refined overlays can use `super` as the basis for building new packages, and `self` as a way to query
the final result of the fix-point.
An example of overlay which extends Nixpkgs with a small set of packages can be found at:
https://github.com/nbp/nixpkgs-mozilla/blob/nixpkgs-overlay/moz-overlay.nix
To use this file, checkout the repository and add a symbolic link to
the `moz-overlay.nix` file in `~/.nixpkgs/overlays` directory.
I wanted to list the different texlive collections using the nix-repl, as per the [manual](https://nixos.org/nixpkgs/manual/#idm140737316065984).
It didn't work, since the nixpkgs were not loaded. Doing `:l <nixpkgs>` first resolved the problem.
This change adds the nixpkgs loading step to the manual so that the next inexperienced person don't have to figure out why it didn't work.
I tested this on NixOS unstable (16.09pre90254.6b20d5b) with nix-repl 1.11.3.
In #19309 a separate output for tkinter was added.
Several dependencies of Python depend indirectly on Python. We have the
following two paths:
```
‘python-2.7.12’ - ‘tk-8.6.6’ - ‘libXft-2.3.2’ - ‘libXrender-0.9.10’ -
‘libX11-1.6.4’ - ‘libxcb-1.12’ - ‘libxslt-1.1.29’- ‘libxml2-2.9.4’ -
‘python-2.7.12’
‘python-2.7.12’ - ‘tk-8.6.6’ - ‘libXft-2.3.2’ - ‘fontconfig-2.12.1’ -
‘dejavu-fonts-2.37’ - ‘fontforge-20160404’ - ‘python-2.7.12’
```
Because only `tkinter` needs this, I added
```
pythonSmall = python.override {x11Support = false;};
```
to break the infinite recursion. We also still have the output
`tkinter`.
However, we might as well build without x11Support by default. Then we build with x11Support as well so we get the tkinter module and put that in a separate package.
`stripHash` documentation states that it prints out the stripped name to
the stdout, but the function stored the value in `strippedName`
instead.
Basically all usages did something like
`$(stripHash $foo | echo $strippedName)` which is just braindamaged.
Fixed the implementation and all invocations.
This is similar to `overrideDerivation`, but overrides the arguments to
`mkDerivation` instead of the underlying `derivation` call.
Also update `makeOverridable` so that uses of `overrideAttrs` can be
followed by `override` and `overrideDerivation`, i.e. they can be
mix-and-matched.
They now go to devman, devdoc, or $outputMan, in that order. This is
to prevent cases such as the man-pages package quietly losing its
section 3 pages.
