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.

doc/middleclick-autoscroll.1.scd

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+middleclick-autoscroll(1)
+
+# NAME
+
+middleclick-autoscroll - middle-click autoscroll for Chromium-based applications
+
+# SYNOPSIS
+
+*middleclick-autoscroll* [_command_]
+
+# DESCRIPTION
+
+Blink, the engine inside Chromium, Electron and CEF, implements Windows-style
+autoscroll: hold the middle mouse button and the page scrolls with the pointer.
+On Linux it is switched off, because middle click is taken by primary-selection
+paste. It can be turned back on with *--enable-blink-features=MiddleClickAutoscroll*
+on the command line.
+
+*middleclick-autoscroll* finds every Chromium-based application on the system
+and puts that argument somewhere the application will actually read it, then
+keeps doing so for anything installed later.
+
+Run without a command it shows an interactive menu. Everything it can be told
+is reachable from there; the configuration file behind it does not need to be
+edited by hand.
+
+Nothing outside the user's home directory is written to, and running it as root
+is refused.
+
+# COMMANDS
+
+*enable*
+	Turn autoscroll on, apply it to everything installed, and start watching
+	for new applications.
+
+*disable*
+	Turn it off and put every file that was changed back the way it was.
+
+*apply*
+	Apply to anything that has appeared since the last run. This is what the
+	watcher calls; running it by hand is only needed when the watcher is off.
+
+*status*
+	How many applications are covered, whether Steam is patched, and when the
+	last run was.
+
+*list*
+	Every Chromium-based application that was found, and how each one is
+	handled.
+
+*-h*, *--help*
+	Show a summary of the commands.
+
+*-V*, *--version*
+	Show the version.
+
+# HOW THE ARGUMENT GETS IN
+
+Two ways, chosen per application.
+
+*Flag file*
+	Arch's Electron and Chromium wrappers read extra arguments from
+	_$XDG_CONFIG_HOME/<name>-flags.conf_. This is the preferred route: it is
+	the supported way to pass arguments, it survives package upgrades, and it
+	applies to a launch from a terminal as much as one from the menu. An
+	*--enable-blink-features* line that is already in the file is extended
+	rather than duplicated - Chromium keeps only the last occurrence of that
+	option, so a second one would switch the first one off.
+
+*Desktop entry*
+	For applications that ship their own binary with no wrapper, and for
+	Flatpaks, a copy of the desktop entry with the argument appended is written
+	to _~/.local/share/applications_, where it shadows the system one. Entries
+	that already live there - AppImages, web app shortcuts - are edited in
+	place, with the original kept. Every generated entry is marked with
+	*X-MCA-Generated*; an entry that is not marked is somebody else's and is
+	left alone.
+
+Programs that start themselves at login write their own entry into
+_~/.config/autostart_ pointing straight at their binary, bypassing the menu
+entry entirely. Those are patched in place as well.
+
+# STEAM
+
+Steam's interface is CEF and supports the feature, but Steam builds the command
+line for its web helper itself. The only way in 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 that Steam no
+longer repairs a damaged installation on its own; that is why Steam is a switch
+of its own in the settings.
+
+Starting Steam from a terminal without *-noverifyfiles* undoes the patch for
+that session. The watcher notices and puts it back, so the next start has it
+again.
+
+# SPOTIFY
+
+The official client is CEF rather than Electron. Installed through
+*spotify-launcher*, it is started by a program that builds its own command line
+and has a configuration file with a slot for extra arguments; that slot is
+where the flag goes. Installed as a plain package, it is an ordinary desktop
+entry and needs nothing special.
+
+# WHAT CANNOT BE DETECTED
+
+An AppImage keeps its payload in a compressed filesystem, so there is no way to
+tell from the outside whether it contains Chromium. Those are listed as *cannot
+tell* and left alone until they are switched on from the applications screen.
+
+# FILES
+
+_~/.config/middleclick-autoscroll/config_
+	Written by the program. Every option in it is reachable from the menu.
+
+_~/.local/state/middleclick-autoscroll/ledger_
+	One line per change, so *disable* can undo exactly what was done and
+	nothing else.
+
+_~/.local/state/middleclick-autoscroll/backup/_
+	Copies of the files that are edited in place rather than shadowed.
+
+_~/.cache/middleclick-autoscroll/detect_
+	Which programs were found to be Chromium, keyed by size and modification
+	time. Safe to delete.
+
+# ENVIRONMENT
+
+*NO_COLOR*
+	Disables colour.
+
+# SEE ALSO
+
+*systemctl*(1), *flatpak*(1)
+
+# AUTHORS
+
+Felitendo. Source and issue tracker at
+https://github.com/Felitendo/middleclick-autoscroll