fix: keep the unsupported-flag warning off browsers

--enable-blink-features is on the list of flags Chromium warns about, so every
browser the flag was applied to put a yellow "unsupported command-line flag"
bar above each page.

Browsers are given --enable-features=MiddleClickAutoscroll instead. It asks for
the same thing - Blink generates a feature of the same name for each of its
runtime flags - and is not on that list. That spelling only works from Chromium
124 onwards, so everything else keeps the flag that works everywhere: an
application embedding an older Chromium, Steam's CEF among them, has no such
bar to show anyway.

Helium knows the feature under a name of its own and ignores the Chromium one,
so browsers are asked for HeliumMiddleClickAutoscroll as well; autoscroll never
worked there before. A name a browser does not know is ignored, which is what
makes one list safe for all of them.

An installation set up by an earlier version is taken back and written again
once, because a file that is already marked as patched would otherwise be left
alone with the old flag in it.

README.md

@@ -101,6 +101,19 @@ flag turns it on:
 But doing that for every app is kinda bothersome and it also might break with updates.
 That's why I created this small tool to automate that.
 
+Browsers get the same thing asked for differently:
+
+--enable-features=MiddleClickAutoscroll
+
+Both mean the same feature - Blink generates a matching feature name for each of
+its runtime flags - but the first one is on Chromium's list of flags worth
+warning about, so a browser started with it shows a yellow "unsupported
+command-line flag" bar over every page. The second one is not on that list, so
+there's no bar. It only works from Chromium 124 on, which is why apps that
+embed something older (Steam's CEF, older Electron) keep the first one - they
+have no such bar to begin with. Helium, which carries the feature under its own
+name, is asked for `HeliumMiddleClickAutoscroll` alongside it.
+
 New apps are picked up by a systemd path unit that watches the
 relevant directories. Without systemd, `middleclick-autoscroll apply` does the
 same thing manually.

doc/middleclick-autoscroll.1.scd

@@ -18,7 +18,18 @@ 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. It works on any distribution:
+keeps doing so for anything installed later.
+
+A browser is given *--enable-features=MiddleClickAutoscroll* instead. It asks
+for the same feature - Blink generates a feature of that name for each of its
+runtime flags - but it is not on the list of flags Chromium warns about, so the
+browser does not put a bar reading "You are using an unsupported command-line
+flag" above every page. That spelling only works from Chromium 124 onwards,
+which is why everything else keeps the first one: an application that embeds an
+older Chromium, such as Steam's CEF, has no such bar to show anyway. Helium
+knows the feature under a name of its own and is asked for
+*HeliumMiddleClickAutoscroll* as well; a name a browser does not know is
+ignored. It works on any distribution:
 which of the routes below an application takes is read off its launcher, not
 assumed from where the launcher came from.
 
@@ -71,10 +82,10 @@ Two ways, chosen per application.
 	Where the launcher reads 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
+	applies to a launch from a terminal as much as one from the menu. A
-	*--enable-blink-features* line that is already in the file is extended
+	feature list that is already in the file is extended rather than
-	rather than duplicated - Chromium keeps only the last occurrence of that
+	duplicated - Chromium keeps only the last occurrence of such an option, so
-	option, so a second one would switch the first one off.
+	a second one would switch the first one off.
 
 	Arch's Electron and Chromium packages all wrap their binaries this way, and
 	so do a number of individual vendors' launchers elsewhere. Whether a given

src/lib/apply.sh

@@ -66,6 +66,15 @@ mca_apply() {
 	MCA_N_ON=0; MCA_N_OFF=0; MCA_N_UNKNOWN=0
 
 	mca_config_load
+
+	# An installation that was set up by a version whose answer was a different
+	# flag still has that flag where it put it, and nothing below would touch it
+	# again: a file that is already marked as patched is left alone. Taking
+	# everything back once, here, is what carries such an installation over.
+	if [[ "$(mca_state_read flag_scheme 1)" != "$MCA_FLAG_SCHEME" ]]; then
+		mca_revert_all
+	fi
+
 	mca_scan
 
 	for i in "${!MCA_IDS[@]}"; do
@@ -87,10 +96,11 @@ mca_apply() {
 
 		case "$route" in
 			flags)
-				mca_flags_apply "$prog" || mca_desktop_apply "$id" "$file"
+				mca_flags_apply "$prog" "$kind" \
+					|| mca_desktop_apply "$id" "$file" "$(mca_flags "$kind")"
 				;;
 			desktop)
-				mca_desktop_apply "$id" "$file"
+				mca_desktop_apply "$id" "$file" "$(mca_flags "$kind")"
 				;;
 			steam)
 				mca_steam_desktop_apply "$id" "$file" "$packaging"
@@ -143,6 +153,7 @@ mca_apply() {
 	fi
 
 	mca_state_write last_apply "$(date +%s)"
+	mca_state_write flag_scheme "$MCA_FLAG_SCHEME"
 	return 0
 }
 

src/lib/common.sh

@@ -13,11 +13,42 @@ MCA_PRETTY="Middle-Click Autoscroll"
 # The whole point of the package. Blink implements Windows-style autoscroll
 # behind a runtime flag that Chromium does not turn on for Linux, because
 # middle click is taken by primary-selection paste there.
+#
+# There are two ways to ask for that flag, and which one is right depends on
+# what is being started:
+#
+#   --enable-blink-features=MiddleClickAutoscroll is the one that works
+#   everywhere, and the only one that works in the Chromium versions embedded
+#   applications ship - Steam's CEF, an Electron a few years old, anything
+#   before Chromium 124. A browser started with it puts a yellow bar above the
+#   page saying an unsupported command line flag is in use, because Chromium
+#   keeps a list of flags worth warning about and this is on it.
+#
+#   --enable-features=MiddleClickAutoscroll is not on that list, so a browser
+#   started with it says nothing. Blink generates a feature of the same name
+#   for every one of its runtime flags, which is what makes the two the same
+#   request - but only since Chromium 124. Before that the name means nothing
+#   and is ignored without a word.
+#
+# So a browser, which is the only thing that shows the bar and the one thing
+# that keeps itself up to date, is given the quiet one; everything else keeps
+# the one that always works.
 MCA_FLAG="--enable-blink-features=MiddleClickAutoscroll"
 
-# The Blink feature name on its own, for merging into an --enable-blink-features
+# Helium ships the feature under its own name and does not answer to the
-# list that an app (or the user) already carries.
+# Chromium one, so browsers are asked for both. A name a browser does not know
+# is ignored, which is what makes one list safe to hand to all of them.
+MCA_BROWSER_FLAG="--enable-features=MiddleClickAutoscroll,HeliumMiddleClickAutoscroll"
+
+# The feature names on their own, for merging into a list that an application
+# (or the user) already carries, and for taking them back out again.
 MCA_FEATURE="MiddleClickAutoscroll"
+MCA_BROWSER_FEATURES="MiddleClickAutoscroll,HeliumMiddleClickAutoscroll"
+
+# Bumped when the flags above change. An installation that was set up by a
+# version with a different answer is taken back and done again once, because a
+# file that is already patched is otherwise left alone. See mca_apply.
+MCA_FLAG_SCHEME=2
 
 MCA_LIBDIR="${MCA_LIBDIR:-@LIBDIR@}"
 MCA_LOCALEDIR="${MCA_LOCALEDIR:-@LOCALEDIR@}"

src/lib/config.sh

@@ -154,10 +154,18 @@ mca_config_load() {
 	CFG_SKIP="$(mca_config_get Skip '')"
 }
 
+# mca_flags [kind]
 # The full argument string that gets injected. Kept in one place so the flag
 # file writer and the desktop entry writer cannot drift apart.
+#
+# A browser gets the flag that leaves it without a warning bar; everything else
+# gets the one that works in every Chromium there is. See MCA_FLAG.
 mca_flags() {
-	printf '%s' "$MCA_FLAG"
+	if [[ ${1:-app} == browser ]]; then
+		printf '%s' "$MCA_BROWSER_FLAG"
+	else
+		printf '%s' "$MCA_FLAG"
+	fi
 	[[ -n ${CFG_EXTRA_FLAGS:-} ]] && printf ' %s' "$CFG_EXTRA_FLAGS"
 	printf '\n'
 }

src/lib/patch.sh

@@ -29,6 +29,40 @@
 MCA_MARK_BEGIN='# >>> middleclick-autoscroll'
 MCA_MARK_END='# <<< middleclick-autoscroll'
 
+# ---------------------------------------------------------------------------
+# Feature lists
+# ---------------------------------------------------------------------------
+# Both --enable-features and --enable-blink-features take a comma separated
+# list, and Chromium keeps the last one it is given and drops the rest. A
+# second one of the same kind would therefore silently switch off whatever the
+# first one turned on, so an option that is already there is extended instead.
+
+# _mca_list_merge <list> <wanted>
+# The two lists as one, in the order they came and without repeating anything.
+_mca_list_merge() {
+	local out="$1" item
+	for item in ${2//,/ }; do
+		[[ ",$out," == *",$item,"* ]] && continue
+		out="${out:+$out,}$item"
+	done
+	printf '%s' "$out"
+}
+
+# _mca_list_strip <list> <unwanted>
+# The list without any of the named entries.
+_mca_list_strip() {
+	local out='' item
+	for item in ${1//,/ }; do
+		[[ ",$2," == *",$item,"* ]] && continue
+		out="${out:+$out,}$item"
+	done
+	printf '%s' "$out"
+}
+
+# The two options, as a regular expression branch, for the places that have to
+# recognise either of them.
+MCA_FEATURE_OPTS='--enable-blink-features|--enable-features'
+
 # ---------------------------------------------------------------------------
 # Command lines
 # ---------------------------------------------------------------------------
@@ -70,28 +104,32 @@ _mca_exec_after_program() {
 # Prints nothing and returns 1 when there was nothing to change, so callers can
 # tell a real edit from a no-op without diffing.
 #
-# An --enable-blink-features that is already there is extended rather than
+# A feature list that is already on the line is extended rather than repeated.
-# repeated: Chromium keeps the last occurrence of the option and drops the
+# See _mca_list_merge.
-# rest, so a second one would silently disable whatever the first turned on.
 mca_exec_inject() {
 	local line="$1" flagstr="${2:-}" where="${3:-before-fields}"
-	local flag value existing at changed=0
+	local flag opt value existing merged re at changed=0
 	local -a flags
 
 	[[ -n $flagstr ]] || flagstr="$(mca_flags)"
 	read -r -a flags <<< "$flagstr"
 
 	for flag in "${flags[@]}"; do
-		if [[ $flag == --enable-blink-features=* ]]; then
+		case "$flag" in
-			value="${flag#--enable-blink-features=}"
+			--enable-blink-features=*|--enable-features=*)
-			if [[ $line =~ --enable-blink-features=([A-Za-z0-9,_-]*) ]]; then
+				opt="${flag%%=*}"
-				existing="${BASH_REMATCH[1]}"
+				value="${flag#*=}"
-				[[ ",$existing," == *",$value,"* ]] && continue
+				re="(^|[[:space:]])$opt=([^[:space:]]*)"
-				line="${line/--enable-blink-features=$existing/--enable-blink-features=${existing:+$existing,}$value}"
+				if [[ $line =~ $re ]]; then
-				changed=1
+					existing="${BASH_REMATCH[2]}"
-				continue
+					merged="$(_mca_list_merge "$existing" "$value")"
-			fi
+					[[ $merged == "$existing" ]] && continue
-		fi
+					line="${line/$opt=$existing/$opt=$merged}"
+					changed=1
+					continue
+				fi
+				;;
+		esac
 
 		[[ " $line " == *" $flag "* ]] && continue
 
@@ -117,12 +155,12 @@ mca_exec_inject() {
 # Flag files
 # ---------------------------------------------------------------------------
 
-# mca_flags_apply <program>
+# mca_flags_apply <program> [kind]
 # Writes the flags into the file the program's launcher reads. Returns 0 when
 # the program has such a file (whether or not anything needed changing), 1 when
 # it has none and the desktop entry route has to be used instead.
 mca_flags_apply() {
-	local prog="$1" name target='' existing_target=''
+	local prog="$1" kind="${2:-app}" name target='' existing_target=''
 	local -a candidates=()
 
 	mapfile -t candidates < <(mca_flags_candidates "$prog" | awk '!seen[$0]++')
@@ -133,7 +171,7 @@ mca_flags_apply() {
 	for name in "${candidates[@]}"; do
 		if [[ -f "$MCA_XDG_CONFIG/$name" ]]; then
 			existing_target="$name"
-			_mca_flags_write "$MCA_XDG_CONFIG/$name"
+			_mca_flags_write "$MCA_XDG_CONFIG/$name" "$kind"
 		fi
 	done
 	[[ -n $existing_target ]] && return 0
@@ -143,19 +181,21 @@ mca_flags_apply() {
 	# creating that one also covers every other application using the same
 	# shared Electron.
 	target="${candidates[-1]}"
-	_mca_flags_write "$MCA_XDG_CONFIG/$target"
+	_mca_flags_write "$MCA_XDG_CONFIG/$target" "$kind"
 	return 0
 }
 
-# _mca_flags_write <file>
+# _mca_flags_write <file> [kind]
-# Adds the flags as a marked block, or merges into an --enable-blink-features
+# Adds the flags as a marked block, or merges into a feature list that is
-# line that is already in the file.
+# already in the file.
 _mca_flags_write() {
-	local file="$1" content='' line flag value existing merged=0 block=''
+	local file="$1" kind="${2:-app}"
+	local content='' line flag opt want existing merged=0 block=''
 	local -a flags
+	local -A merged_opts=()
 	local created=0
 
-	read -r -a flags <<< "$(mca_flags)"
+	read -r -a flags <<< "$(mca_flags "$kind")"
 
 	[[ -f $file ]] || created=1
 	if (( ! created )); then
@@ -166,16 +206,23 @@ _mca_flags_write() {
 		fi
 	fi
 
-	# Merge into a blink-features line the user (or a distribution) put there.
+	# Merge into a feature list the user (or a distribution) put there, rather
-	if [[ $content == *--enable-blink-features=* ]]; then
+	# than write a second line of the same option further down.
+	if [[ $content == *--enable-* ]]; then
 		local out=''
 		while IFS= read -r line; do
-			if [[ $line =~ ^[[:space:]]*--enable-blink-features=([A-Za-z0-9,_-]*)[[:space:]]*$ ]]; then
+			if [[ $line =~ ^[[:space:]]*($MCA_FEATURE_OPTS)=([^[:space:]]*)[[:space:]]*$ ]]; then
-				existing="${BASH_REMATCH[1]}"
+				opt="${BASH_REMATCH[1]}"
-				if [[ ",$existing," != *",$MCA_FEATURE,"* ]]; then
+				existing="${BASH_REMATCH[2]}"
-					line="--enable-blink-features=${existing:+$existing,}$MCA_FEATURE"
+				want=''
+				for flag in "${flags[@]}"; do
+					[[ $flag == "$opt="* ]] && want="${flag#*=}"
+				done
+				if [[ -n $want ]]; then
+					line="$opt=$(_mca_list_merge "$existing" "$want")"
+					merged_opts["$opt"]=1
+					merged=1
 				fi
-				merged=1
 			fi
 			out+="$line"$'\n'
 		done <<< "$content"
@@ -183,7 +230,7 @@ _mca_flags_write() {
 	fi
 
 	for flag in "${flags[@]}"; do
-		(( merged )) && [[ $flag == --enable-blink-features=* ]] && continue
+		[[ -n ${merged_opts["${flag%%=*}"]:-} ]] && continue
 		block+="$flag"$'\n'
 	done
 
@@ -218,7 +265,7 @@ _mca_flags_drop_block() {
 
 # mca_flags_revert <file> <detail>
 mca_flags_revert() {
-	local file="$1" detail="$2" content line out='' existing new
+	local file="$1" detail="$2" content line out='' opt existing new
 
 	[[ -f $file ]] || return 0
 
@@ -238,12 +285,13 @@ mca_flags_revert() {
 
 	if [[ $detail == merged* ]]; then
 		while IFS= read -r line; do
-			if [[ $line =~ ^[[:space:]]*--enable-blink-features=([A-Za-z0-9,_-]*)[[:space:]]*$ ]]; then
+			if [[ $line =~ ^[[:space:]]*($MCA_FEATURE_OPTS)=([^[:space:]]*)[[:space:]]*$ ]]; then
-				existing="${BASH_REMATCH[1]}"
+				opt="${BASH_REMATCH[1]}"
-				new="${existing//$MCA_FEATURE/}"
+				existing="${BASH_REMATCH[2]}"
-				new="${new//,,/,}"; new="${new#,}"; new="${new%,}"
+				# Either name, whichever version of this program put it there.
+				new="$(_mca_list_strip "$existing" "$MCA_BROWSER_FEATURES")"
 				[[ -z $new ]] && continue
-				line="--enable-blink-features=$new"
+				line="$opt=$new"
 			fi
 			out+="$line"$'\n'
 		done <<< "$content"
@@ -419,15 +467,17 @@ _mca_entry_patch_inplace() {
 			*)       mca_is_chromium "$prog" || return 0 ;;
 		esac
 
+		mca_desktop_is_browser && kind=browser || kind=app
+
 		if [[ $gate == autostart ]]; then
 			[[ $CFG_AUTOSTART == yes ]] || return 0
 		else
 			id="${file##*/}"; id="${id%.desktop}"
-			mca_desktop_is_browser && kind=browser || kind=app
 			mca_kind_wanted "$kind" "$id" "$packaging" || return 0
 		fi
 
-		content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE")"
+		content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE" \
+			"$(mca_flags "$kind")")"
 	fi
 
 	[[ -n $content ]] || return 0