Address PR comments

runtime/lua/man.lua

@@ -1,8 +1,10 @@
-local function highlight_formatted(line, linenr)
+local buf_hls = {}
+
+local function highlight_line(line, linenr)
   local chars = {}
   local prev_char = ''
   local overstrike, escape = false, false
-  local hls = {} -- Store highlight groups as { attr, start, end }
+  local hls = {} -- Store highlight groups as { attr, start, final }
   local NONE, BOLD, UNDERLINE, ITALIC = 0, 1, 2, 3
   local hl_groups = {[BOLD]="manBold", [UNDERLINE]="manUnderline", [ITALIC]="manItalic"}
   local attr = NONE
@@ -10,40 +12,40 @@ local function highlight_formatted(line, linenr)
 
   local function end_attr_hl(attr)
     for i, hl in ipairs(hls) do
-      if hl[1] == attr and hl[3] == -1 then
-        hl[3] = byte
+      if hl.attr == attr and hl.final == -1 then
+        hl.final = byte
         hls[i] = hl
       end
     end
   end
 
   local function add_attr_hl(code)
-    local on = true
+    local continue_hl = true
     if code == 0 then
       attr = NONE
-      on = false
+      continue_hl = false
     elseif code == 1 then
       attr = BOLD
-    elseif code == 21 or code == 22 then
+    elseif code == 22 then
       attr = BOLD
-      on = false
+      continue_hl = false
     elseif code == 3 then
       attr = ITALIC
     elseif code == 23 then
       attr = ITALIC
-      on = false
+      continue_hl = false
     elseif code == 4 then
       attr = UNDERLINE
     elseif code == 24 then
       attr = UNDERLINE
-      on = false
+      continue_hl = false
     else
       attr = NONE
       return
     end
 
-    if on then
-      hls[#hls + 1] = {attr, byte, -1}
+    if continue_hl then
+      hls[#hls + 1] = {attr=attr, start=byte, final=-1}
     else
       if attr == NONE then
         for a, _ in pairs(hl_groups) do
@@ -55,12 +57,15 @@ local function highlight_formatted(line, linenr)
     end
   end
 
-  -- Break input into UTF8 characters
+  -- Break input into UTF8 code points. ASCII code points (from 0x00 to 0x7f)
+  -- can be represented in one byte. Any code point above that is represented by
+  -- a leading byte (0xc0 and above) and continuation bytes (0x80 to 0xbf, or
+  -- decimal 128 to 191).
   for char in line:gmatch("[^\128-\191][\128-\191]*") do
     if overstrike then
       local last_hl = hls[#hls]
       if char == prev_char then
-        if char == '_' and attr == UNDERLINE and last_hl and last_hl[3] == byte then
+        if char == '_' and attr == UNDERLINE and last_hl and last_hl.final == byte then
           -- This underscore is in the middle of an underlined word
           attr = UNDERLINE
         else
@@ -72,21 +77,21 @@ local function highlight_formatted(line, linenr)
       elseif prev_char == '+' and char == 'o' then
         -- bullet (overstrike text '+^Ho')
         attr = BOLD
-        char = [[·]]
-      elseif prev_char == [[·]] and char == 'o' then
+        char = '·'
+      elseif prev_char == '·' and char == 'o' then
         -- bullet (additional handling for '+^H+^Ho^Ho')
         attr = BOLD
-        char = [[·]]
+        char = '·'
       else
         -- use plain char
         attr = NONE
       end
 
       -- Grow the previous highlight group if possible
-      if last_hl and last_hl[1] == attr and last_hl[3] == byte then
-        last_hl[3] = byte + #char
+      if last_hl and last_hl.attr == attr and last_hl.final == byte then
+        last_hl.final = byte + #char
       else
-        hls[#hls + 1] = {attr, byte, byte + #char}
+        hls[#hls + 1] = {attr=attr, start=byte, final=byte + #char}
       end
 
       overstrike = false
@@ -96,15 +101,19 @@ local function highlight_formatted(line, linenr)
     elseif escape then
       -- Use prev_char to store the escape sequence
       prev_char = prev_char .. char
-      local sgr = prev_char:match("^%[([\020-\063]*)m$")
+      -- We only want to match against SGR sequences, which consist of ESC
+      -- followed by '[', then a series of parameter and intermediate bytes in
+      -- the range 0x20 - 0x3f, then 'm'. (See ECMA-48, sections 5.4 & 8.3.117)
+      local sgr = prev_char:match("^%[([\032-\063]*)m$")
       if sgr then
         local match = ''
         while sgr and #sgr > 0 do
+          -- Match against SGR parameters, which may be separated by ';'
           match, sgr = sgr:match("^(%d*);?(.*)")
           add_attr_hl(match + 0) -- coerce to number
         end
         escape = false
-      elseif not prev_char:match("^%[[\020-\063]*$") then
+      elseif not prev_char:match("^%[[\032-\063]*$") then
         -- Stop looking if this isn't a partial CSI sequence
         escape = false
       end
@@ -122,20 +131,38 @@ local function highlight_formatted(line, linenr)
     end
   end
 
-  for i, hl in ipairs(hls) do
-    if hl[1] ~= NONE then
-      vim.api.nvim_buf_add_highlight(
+  for _, hl in ipairs(hls) do
+    if hl.attr ~= NONE then
+      buf_hls[#buf_hls + 1] = {
         0,
         -1,
-        hl_groups[hl[1]],
+        hl_groups[hl.attr],
         linenr - 1,
-        hl[2],
-        hl[3]
-      )
+        hl.start,
+        hl.final
+      }
     end
   end
 
   return table.concat(chars, '')
 end
 
-return { highlight_formatted = highlight_formatted }
+local function highlight_man_page()
+  local mod = vim.api.nvim_eval("&modifiable")
+  vim.api.nvim_command("set modifiable")
+
+  local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+  for i, line in ipairs(lines) do
+    lines[i] = highlight_line(line, i)
+  end
+  vim.api.nvim_buf_set_lines(0, 0, -1, false, lines)
+
+  for _, args in ipairs(buf_hls) do
+    vim.api.nvim_buf_add_highlight(unpack(args))
+  end
+  buf_hls = {}
+
+  vim.api.nvim_command("let &modifiable = "..mod)
+end
+
+return { highlight_man_page = highlight_man_page }