middleclick-autoscroll 1.0.0

Middle-click autoscroll for every Chromium-based application on the system:
Electron and CEF applications, Chromium-based browsers, Flatpaks, Spotify and
Steam, plus anything installed later.

The flag goes into an Arch wrapper's <name>-flags.conf where one exists, and
into a shadowing desktop entry where it does not. Steam gets its web helper
script patched and -noverifyfiles on its launcher, because it restores its own
files otherwise. Every change is recorded so it can be taken back exactly.

README.md

@@ -0,0 +1,191 @@
+# middleclick-autoscroll
+
+Middle-click autoscroll — hold the middle mouse button, move the pointer, the
+page scrolls — for every Chromium-based application on the system. Discord,
+Vesktop, Equibop, VS Code, Obsidian, Signal, Spotify, Steam, Chromium-based
+browsers, and whatever gets installed next week.
+
+```bash
+paru -S middleclick-autoscroll
+middleclick-autoscroll enable
+```
+
+That is the whole setup. Nothing else has to be configured, and no file has to
+be edited.
+
+## Why this needs a program at all
+
+Blink — the engine inside Chromium, Electron and CEF — has had Windows-style
+autoscroll for years. On Linux it is switched off, because middle click is
+already taken by primary-selection paste. One command line argument turns it
+back on:
+
+```
+--enable-blink-features=MiddleClickAutoscroll
+```
+
+Getting that argument into one application is a five-minute job. Getting it into
+all of them, in a way that survives the next package upgrade, is not:
+
+- Some applications read a flag file, some don't.
+- Some ship their own copy of Electron, some use the system one.
+- Flatpaks see none of the host's configuration.
+- An application that starts itself at login uses a different entry than the one
+  in the menu, and Discord launched at login used to behave differently from
+  Discord launched by hand.
+- Steam takes no arguments for its interface at all, and puts back any file you
+  change.
+- Every upgrade can undo the lot.
+
+## The interface
+
+`middleclick-autoscroll` on its own:
+
+```
+  Middle-Click Autoscroll
+
+  Autoscroll                     ON
+
+  Applications covered           14 of 15
+  Not identified                 1 - see the applications list
+  Steam                          ON
+  New applications               ON
+  Last applied                   3 minutes ago
+
+  Applications pick this up the next time they are started.
+
+  [1] Turn autoscroll on or off
+  [2] Apply now
+  [3] Applications
+  [4] Settings
+  [q] Quit
+```
+
+**[3] Applications** lists everything that was found, how each one is handled,
+and lets a single application be switched off — or an unrecognised one switched
+on — with the space bar:
+
+```
+  Applications
+
+  ▸ Vesktop                            on (flag file)
+    Discord                            on (flag file)
+    Code - OSS                         on (flag file)
+    Obsidian                           on (flag file)
+    Signal                             on (flag file)
+    Spotify                            on (launcher)
+    Steam                              on (Steam)
+    Cursor                             cannot tell
+```
+
+**[4] Settings** has the categories — Electron and CEF applications, browsers,
+Flatpaks, autostart entries, Steam, Spotify, whether to watch for new
+applications, and a field for extra Chromium arguments if you want any.
+
+There is a configuration file behind all of this. You are never asked to open
+it.
+
+## Where the argument actually goes
+
+Two routes, picked per application.
+
+| | |
+|---|---|
+| **Flag file** | Arch's Electron and Chromium wrappers read extra arguments from `~/.config/<name>-flags.conf`. This is the good one: it is the supported way to pass arguments, it survives package upgrades untouched, and it applies to a launch from a terminal as much as one from the menu. |
+| **Desktop entry** | For applications that ship their own binary with no wrapper, and for Flatpaks, a copy of the entry with the argument appended goes into `~/.local/share/applications`, where it shadows the system one. |
+
+Entries that already live in `~/.local/share/applications` — AppImages, web app
+shortcuts — are edited in place and the original is kept. So are the entries in
+`~/.config/autostart`, so an application that starts itself at login gets the
+same treatment as one started from the menu.
+
+An `--enable-blink-features` that is already there is **extended**, never
+repeated. Chromium keeps only the last occurrence of that option, so a second
+one would silently switch off whatever the first one enabled.
+
+## Steam
+
+Steam's interface is CEF and supports the feature perfectly well, but Steam
+builds the command line for its web helper itself and offers no way to add to
+it. The only place an argument fits is the script that starts the helper, inside
+Steam's own installation:
+
+```
+~/.local/share/Steam/ubuntu12_64/steamwebhelper_sniper_wrap.sh
+```
+
+Steam checksums that script at every start and restores it when it differs, so
+its launcher entry also gets `-noverifyfiles`. **The trade-off is real**: with
+verification off, Steam no longer repairs a damaged installation by itself. That
+is why Steam is a switch of its own rather than part of the general handling —
+turn it off in the settings and Steam is left completely alone.
+
+The script comes back on every client update. The watcher notices and puts the
+patch back.
+
+Starting Steam from a terminal without `-noverifyfiles` undoes it for that one
+session; the next start from the menu has it again.
+
+## Applications installed later
+
+A systemd user path unit watches every directory a launcher can appear in —
+`/usr/share/applications`, the Flatpak exports, `~/.local/share/applications`,
+`~/.config/autostart` — plus Steam's helper script. Anything new is handled
+within a second of being installed, whether it came from pacman, the AUR,
+Flatpak or an AppImage manager. There is no hook to install per package manager.
+
+## What it will not guess
+
+An AppImage keeps its payload in a compressed filesystem, so there is no way to
+tell from the outside whether Chromium is in there. Those show up as **cannot
+tell** and are left alone until you switch them on from the applications screen.
+
+Detection is deliberately conservative everywhere else too. A wrong "yes" would
+append an unknown argument to something that is not Chromium, and plenty of
+programs treat an unrecognised argument as a file name to open.
+
+## Undoing it
+
+```bash
+middleclick-autoscroll disable
+```
+
+Every change is recorded in a ledger as it is made, and `disable` replays it
+backwards: generated entries are deleted, edited files are restored from their
+backups, flag files that only ever contained our line are removed, and a flag
+file that was merged into loses exactly the one feature that was added to it.
+Files that were not touched by this program are not touched by it now either.
+
+Run this before uninstalling the package.
+
+## Commands
+
+| | |
+|---|---|
+| `middleclick-autoscroll` | the menu above |
+| `… enable` | turn it on, apply, start watching |
+| `… disable` | turn it off and put everything back |
+| `… apply` | apply to anything new (this is what the watcher calls) |
+| `… status` | what is covered |
+| `… list` | every application that was found and how it is handled |
+
+See `man middleclick-autoscroll` for the details.
+
+## Requirements
+
+Arch or an Arch derivative (CachyOS, EndeavourOS, Manjaro), bash, systemd for
+the watcher. Nothing outside your home directory is ever written to, and running
+it as root is refused.
+
+## Building from source
+
+```bash
+make
+sudo make install
+```
+
+`make check` runs `bash -n` and, if installed, `shellcheck` over every script.
+
+## License
+
+GPL-3.0-or-later.