stats.lua: page 4 (keys): support help-like terminal printout

While --input-test is useful, and so is page 4 of stats, until now
there was no way to simply print the list in a help-like fashion.

This commit adds such printout, invoked by the script opt
stats-bindlist=yes, which uses the existing page 4 code. This prints
the list on startup and quits immediately - like any help page.

It's awkward to invoke compared to other help pages, and it does
require the stats page to be enabled (it is by default), however
it is a script-generated output, and currently there's no other
method to print a help page generated by a script.

The printout itself is performed using lua's io.write. While reliable,
it's not the standard way for mpv to print to the terminal.

Other possible printout methods are mp.msg.info - which also prints
"[stats]" prefix on each line (ugly), or forcing term-osd and setting
an osd-message which mpv will then print at the terminal - however
that's printed to stderr, and could also be subject to timing concerns
since we quit right afterwards.

In the future we can consider changing/integrating the invocation so
that mpv itself could print a help page generated by a script, thus
solving both the awkward invocation and printout-method issues.

DOCS/man/stats.rst

@@ -197,6 +197,12 @@ The keys are grouped automatically using a simple analysis of the command
 string, and one should not expect documentation-level grouping accuracy,
 however, it should still be reasonably useful.
 
+Using ``--idle --script-opts=stats-bindlist=yes`` will print the list to the
+terminal and quit immediately. By default long lines are shortened to 79 chars,
+and terminal escape sequences are enabled. A different length limit can be
+set by changing ``yes`` to a number (at least 40), and escape sequences can be
+disabled by adding ``-`` before the value, e.g. ``...=-yes`` or ``...=-120``.
+
 Like with ``--input-test``, the list includes bindings from ``input.conf`` and
 from user scripts. Use `--no-config`` to list only built-in bindings.
 

player/lua/stats.lua

@@ -78,6 +78,8 @@ local o = {
     no_ass_b0 = "\027[0m",
     no_ass_it1 = "\027[3m",
     no_ass_it0 = "\027[0m",
+
+    bindlist = "no",  -- print page 4 to the terminal on startup and quit mpv
 }
 options.read_options(o)
 
@@ -395,7 +397,7 @@ local function cmd_subject(cmd)
     return subw:len() > 1 and subw or "[unknown]"
 end
 
-local function get_kbinfo_lines()
+local function get_kbinfo_lines(width)
     -- active keys: only highest priotity of each key, and not our (stats) keys
     local bindings = mp.get_property_native("input-bindings", {})
     local active = {}  -- map: key-name -> bind-info
@@ -458,7 +460,7 @@ local function get_kbinfo_lines()
                                  o.font_mono, kspaces, o.font, 1.3*o.font_size)
     local spost = term and "" or format("{\\u0\\fs%d}", o.font_size)
     local _, itabs = o.indent:gsub("\t", "")
-    local cutoff = term and 79 - o.indent:len() - itabs * 7 - spre:len()
+    local cutoff = term and (width or 79) - o.indent:len() - itabs * 7 - spre:len()
 
     -- create the display lines
     local info_lines = {}
@@ -1147,3 +1149,22 @@ mp.register_event("video-reconfig",
             print_page(curr_page)
         end
     end)
+
+--  --script-opts=stats-bindlist=[-]{yes|<TERM-WIDTH>}
+if o.bindlist ~= "no" then
+    mp.command("no-osd set really-quiet yes")
+    if o.bindlist:sub(1, 1) == "-" then
+        o.bindlist = o.bindlist:sub(2)
+        o.no_ass_b0 = ""
+        o.no_ass_b1 = ""
+    end
+    local width = max(40, math.floor(tonumber(o.bindlist) or 79))
+    mp.add_timeout(0, function()  -- wait for all other scripts to finish init
+        o.ass_formatting = false
+        o.no_ass_indent = " "
+        eval_ass_formatting()
+        io.write(pages[o.key_page_4].desc .. ":" ..
+                 table.concat(get_kbinfo_lines(width)) .. "\n")
+        mp.command("quit")
+    end)
+end