Enable overlay scrollbars in Chromium (#14456)

* Enable overlay scrollbars in Chromium

* Test overlay scrollbar migration

* Simplify Chromium overlay scrollbar migration

---------

Co-authored-by: David Heinemeier Hansson <david@hey.com>

config/chromium-flags.conf

@@ -1,5 +1,5 @@
 --ozone-platform=wayland
 --ozone-platform-hint=wayland
 --password-store=gnome-libsecret
---enable-features=TouchpadOverscrollHistoryNavigation
+--enable-features=TouchpadOverscrollHistoryNavigation,OverlayScrollbar
 --load-extension=/usr/share/omarchy/default/chromium/extensions/copy-url,/usr/share/omarchy/default/chromium/extensions/yt-dlp,/usr/share/omarchy/default/chromium/extensions/whatsapp-slim

migrations/1791376887.sh

@@ -0,0 +1,15 @@
+echo "Enable overlay scrollbars in Chromium-based browsers"
+
+for flags_file in "$HOME"/.config/{chromium,chrome,microsoft-edge-stable,brave,brave-origin}-flags.conf; do
+  [[ -f $flags_file ]] || continue
+  grep -Eq -- '^--enable-features=([^,]+,)*OverlayScrollbar([,:]|$)' "$flags_file" && continue
+
+  if grep -q -- '^--enable-features=' "$flags_file"; then
+    sed -i --follow-symlinks \
+      -e '/^--enable-features=/ s/$/,OverlayScrollbar/' \
+      -e '/^--enable-features=/ s/=,/=/' "$flags_file"
+  else
+    [[ -n $(tail -c1 "$flags_file") ]] && echo >>"$flags_file"
+    echo '--enable-features=OverlayScrollbar' >>"$flags_file"
+  fi
+done

test/shell.d/chromium-overlay-scrollbars-migration-test.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+migration="$ROOT/migrations/1791376887.sh"
+test_tmp=$(mktemp -d)
+trap 'rm -rf "$test_tmp"' EXIT
+
+home="$test_tmp/home"
+config_dir="$home/.config"
+mkdir -p "$config_dir" "$test_tmp/targets"
+
+printf '%s\n' '--enable-features=TouchpadOverscrollHistoryNavigation' >"$config_dir/chromium-flags.conf"
+printf '%s\n' '--enable-features=' >"$config_dir/chrome-flags.conf"
+printf '%s' '--ozone-platform=wayland' >"$config_dir/microsoft-edge-stable-flags.conf"
+printf '%s\n' '--enable-features=BraveFeature' >"$test_tmp/targets/brave-flags.conf"
+ln -s "$test_tmp/targets/brave-flags.conf" "$config_dir/brave-flags.conf"
+
+run_migration() {
+  HOME="$home" bash -euo pipefail "$migration" >/dev/null
+}
+
+run_migration
+run_migration
+
+grep -Fxq -- '--enable-features=TouchpadOverscrollHistoryNavigation,OverlayScrollbar' "$config_dir/chromium-flags.conf" ||
+  fail "the migration preserves existing Chromium features"
+overlay_count=$(grep -o 'OverlayScrollbar' "$config_dir/chromium-flags.conf" | wc -l)
+(( overlay_count == 1 )) || fail "the migration does not duplicate the Chromium feature"
+pass "the migration preserves existing features and can run twice"
+
+[[ $(cat "$config_dir/chrome-flags.conf") == '--enable-features=OverlayScrollbar' ]] ||
+  fail "the migration fills an empty feature list"
+[[ $(cat "$config_dir/microsoft-edge-stable-flags.conf") == $'--ozone-platform=wayland\n--enable-features=OverlayScrollbar' ]] ||
+  fail "the migration adds a feature list with a missing trailing newline"
+pass "the migration handles empty and missing feature lists"
+
+[[ -L $config_dir/brave-flags.conf ]] || fail "the migration preserves symlinked browser flags"
+grep -Fxq -- '--enable-features=BraveFeature,OverlayScrollbar' "$config_dir/brave-flags.conf" ||
+  fail "the migration updates the target of symlinked browser flags"
+pass "the migration follows symlinked browser flags"
+
+[[ ! -e $config_dir/brave-origin-flags.conf ]] || fail "the migration leaves missing browser flags absent"
+pass "the migration skips missing browser flags"