* python3Packages.venvShellHook: add postVenvCreation

* python: docs: add postVenvCreation explaination

Based on some feedback in #87094 and discussion with @fridh, this re-organizes
the onboarding tutorial in the Nixpkgs manual's python section, so that we start
with the simplest, most ad-hoc examples and work our way up. This progresses
from:

1. How to create an temporary python env at the cmdline, then
2. How to create a specific python env for a single script, then
3. How to create a specific python env for a project in a shell.nix, then
4. How to install a specific python env globally on the system or in a user profile.

Additionally, I've tried to standardize on some of the "best practice" ways of
doing things:

1. Instead of saying that this command style is "supported but strongly not
   discouraged", I've just deleted it to avoid confusion.

   Bad:  nix-shell -p python38Packages.numpy python38Packages.toolz
   Good: nix-shell -p 'python38.withPackages(ps: with ps; [ numpy toolz ])'

2. In the portion where we show how to add stuff to the user's
   `XDG_CONFIG_HOME`, use overlays instead of `config.nix`. The former can do
   everything the latter can do, but is also much more generic and powerful,
   because it can compose with other files, compose with other envs, compose
   with overlays that do things like swap whether tensorflow and pytorch are
   built openblas/mkl/cuda stacks, and so on. The user is eventually going to
   see the overlay, so to avoid confusion let's standardize on it.

An overlay by any other name would function just as well, but we generally use
`self: super:` for the regular overlays, and `python-self: python-super`.

Improvement suggested in #87094

tarballs.nixos.org is omitted from the change because urls from there
are always hashed and checked

Since the introduction of php.unwrapped there's no real need for the
phpXXbase attributes, so let's remove them to lessen potential
confusion and clutter. Also update the docs to make it clear how to
get hold of an unwrapped PHP if needed.

This is useful if you need to access the dev output of the unwrapped
derivation.

Co-Authored-By: Jan Tojnar <jtojnar@gmail.com>

Rework withExtensions / buildEnv to handle currently enabled
extensions better and make them compatible with override. They now
accept a function with the named arguments enabled and all, where
enabled is a list of currently enabled extensions and all is the set
of all extensions. This gives us several nice properties:

 - You always get the right version of the list of currently enabled
   extensions

 - Invocations chain

 - It works well with overridden PHP packages - you always get the
   correct versions of extensions

As a contrived example of what's possible, you can add ImageMagick,
then override the version and disable fpm, then disable cgi, and
lastly remove the zip extension like this:

{ pkgs ? (import <nixpkgs>) {} }:
with pkgs;

let
  phpWithImagick = php74.withExtensions ({ all, enabled }: enabled ++ [ all.imagick ]);

  phpWithImagickWithoutFpm743 = phpWithImagick.override {
    version = "7.4.3";
    sha256 = "wVF7pJV4+y3MZMc6Ptx21PxQfEp6xjmYFYTMfTtMbRQ=";
    fpmSupport = false;
  };

  phpWithImagickWithoutFpmZip743 = phpWithImagickWithoutFpm743.withExtensions (
    { enabled, all }:
      lib.filter (e: e != all.zip) enabled);

  phpWithImagickWithoutFpmZipCgi743 = phpWithImagickWithoutFpmZip743.override {
    cgiSupport = false;
  };
in
  phpWithImagickWithoutFpmZipCgi743

For disabling tests when overriding, use `.overridePythonAttrs`.

Discussion about aliasing `.overridePythonAttrs` to `.overrideAttrs`.
https://github.com/NixOS/nixpkgs/pull/82772

This reverts commit 35812875a4.

only very few people followed the strict policy in the last 5 years. the 
maintainers accept backports without reason when it's obvious, so i 
updated the policy to reflect that

This adds some more information to the documentation as well as
addressing review from https://github.com/NixOS/nixpkgs/pull/85636.

This expands the documentation and explains how to assert LP64.

Couple items are outdated. Also they don't belong to documentation -
should go to the issue tracker instead.

* ghcHEAD: bump to 8.11.20200403

* ghcHead: reduce diff vs. 8.10.1

dontAddExtraLibs was removed by accident (IMO) in ea19a8ed1e

* ghcHEAD: add ability to use system libffi

- enable nixpkgs' libffi
- minimise diffs against 8.10.1
- remove patching

* remove configure warning about --with-curses-includes

configure: WARNING: unrecognized options: --with-curses-includes

Fixes #85038

This has changed a few times from 2008 to 2012: cdc74e167, d9213df2c,
and 095db9fe3.

Since this commit on nixos-homepage, the homepage was 404-ing:
179733c176

This provides a means to build a PHP package based on a list of
extensions from another.

For example, to generate a package with all default extensions
enabled, except opcache, but with ImageMagick:

php.withExtensions (e:
  (lib.filter (e: e != php.extensions.opcache) php.enabledExtensions)
  ++ [ e.imagick ])

So now we have only packages for human interaction in php.packages and
only extensions in php.extensions. With this php.packages.exts have
been merged into the same attribute set as all the other extensions to
make it flat and nice.

The nextcloud module have been updated to reflect this change as well
as the documentation.

- Use git.Repo(ROOT, search_parent_directories=True) to find nixpkgs
repo.
- Don't commit overrides.nix.
- Remove "-a" short argument.
- Remove "--commit" flag and commit by default.
- Improve help/error messages.
- Favor closure pattern over classes.Use a closure to wrap the update
function with state rather than a callable class.
- break NixpkgsRepo class into functions
- Optional None-type arguments
- Remove repo checks from update.py. Git is too flexible and permits too
many workflows for my attempt to replace documentation with code to work.
My goal would be to separate the `--add` functionality from the update
functionality in the near term and then there will be no reason for this
usage to create commits anyway.

- update.py's new --add argument replaces manual editing of
vim-plugin-names for basic use cases.

This reverts commit 5e8545e723.

It breaks eval:

attribute 'rev' missing, at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-0-gleber.ewr1.nix.ci/pkgs/top-level/make-tarball.nix:106:39

Also change incorrect 'revision' to 'rev' in the default value for
'nixpkgs' in release.nix.

Fixes https://github.com/NixOS/nixos-homepage/issues/372.

Per review, the input file will now be rewritten automatically if
redirects are found.

Many of the plugins in vim-plugin-names are out of date and redirect to
their new github repos. This commit adds a flag to automatically update
these and defines a process for committing these updates into nixpkgs.

We have now migrated every single Rust package in NixPkgs! This deletes the
legacy fetcher, which is now unused.

Resolves #79975

... to the actually tested one.