HACKING: Recommend a cockpit/tasks based development environment

A lot of newcomers have been struggling with installing a lot of
packages on their distribution (especially Ubuntu). This is also really
not what they should do, as it clutters desktops with a lot of
development dependencies, and then it's still hard to get something
actually working.

Recommend running our cockpit/tasks container in toolbox or distrobox.
This works fine on Fedora, CentOS, RHEL, and Ubuntu, is much easier, safer, and
gives reproducible results.

Move the manual installation of development dependencies to the very end, and
trim and update it a bit.

Fixes cockpit-project#18460

HACKING.md

@@ -8,51 +8,36 @@ Here's where to get the code:
 The remainder of the commands assume you're in the top level of the
 Cockpit git repository checkout.
 
-## Getting the development dependencies
+## Setting up development container
 
-Cockpit uses Node.js during development. Node.js is not used at runtime.
-To make changes on Cockpit you'll want to install Node.js.
+The cockpit team maintains a [cockpit/tasks container](https://quay.io/repository/cockpit/tasks)
+for both local development and CI. If you can install [toolbx](https://containertoolbx.org/) or
+[distrobox](https://distrobox.privatedns.org/) on your system, it is highly
+recommended to do that:
 
-On Debian/Ubuntu:
-
-    sudo apt install nodejs
-
-On Fedora:
-
-    sudo dnf install nodejs
+ - It is *the* official environment for CI, known to work, and gives you reproducible results.
+ - It avoids having to install development packages on your main machine.
+ - It avoids having to map the build and test dependencies to package names of various distributions.
 
-On older OS releases you can use the [n utility](https://github.com/tj/n) to
-get a current version of nodejs.
+On Fedora/CentOS/RHEL based distributions, install toolbox with
 
-When relying on CI to run the test suite, this is all that is necessary to work
-on the JavaScript components of Cockpit.
+    sudo dnf install toolbox
 
-To build the Cockpit binaries from source, required to run the integration tests
-locally (see [testing README](test/README.md)), you will need additional header
-files and other components. The following should work in a fresh Git clone:
+On Debian/Ubuntu based distributions, install it with
 
-    sudo dnf install dnf-utils python-srpm-macros
-    sudo dnf builddep --spec tools/cockpit.spec
+    sudo apt install podman-toolbox
 
-For running the browser unit tests, the following dependencies are required:
+After that, create a cockpit development toolbox:
 
-    sudo dnf install chromium-headless dbus-daemon
+    toolbox create --image quay.io/cockpit/tasks -c cockpit
 
-For running integration tests, the following dependencies are required:
+Enter the toolbox with
 
-    sudo dnf install curl expect xz rpm-build chromium-headless \
-        libvirt-daemon-driver-storage-core libvirt-daemon-driver-qemu libvirt-client python3-libvirt \
-        python3-flake8 python3-pyyaml
+    toolbox enter cockpit
 
-Creating VM images locally (not necessary for running tests) needs the
-following:
-
-    sudo dnf install virt-install
-
-Updating the `node_modules` (in case you need to modify `package.json`)
-requires npm to be installed.
-
-    sudo dnf install npm
+Your home directory, user D-Bus, etc. are shared with the host, so you can e.g.
+edit files as you usually do. Building and running tests happens inside the
+toolbox. If desired, you can install additional packages with `sudo dnf install`.
 
 ## Building
 
@@ -454,3 +439,30 @@ And you can run cockpit-ws and cockpit-bridge under valgrind like this:
 
 Note that cockpit-session and cockpit-bridge will run from the installed
 prefix, rather than your build tree.
+
+## Manually installing the development dependencies
+
+_If at all possible, use the cockpit/tasks container with toolbox/distrobox as
+documented above. Installing all necessary development packages manually on
+your machine is intrusive, error prone, difficult, and hard to debug._
+
+You will need at least node.js and NPM.
+
+On Fedora or CentOS (>= 9):
+
+    sudo dnf install npm
+
+On Debian/Ubuntu:
+
+    sudo apt install npm
+
+For running tests, the following dependencies are required:
+
+    sudo dnf install curl expect xz rpm-build chromium-headless dbus-daemon \
+        libvirt-daemon-driver-storage-core libvirt-daemon-driver-qemu libvirt-client python3-libvirt \
+        python3-flake8 python3-pyyaml
+
+For compiling the C parts, you will need the package build dependencies:
+
+    sudo dnf install dnf-utils python-srpm-macros
+    sudo dnf builddep --spec tools/cockpit.spec