1 files changed, 168 insertions, 0 deletions
diff --git a/runtime/lua/man.lua b/runtime/lua/man.lua
new file mode 100644
index 0000000000..b0fbe9cc35
--- /dev/null
+++ b/runtime/lua/man.lua
@@ -0,0 +1,168 @@
+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, final }
+  local NONE, BOLD, UNDERLINE, ITALIC = 0, 1, 2, 3
+  local hl_groups = {[BOLD]="manBold", [UNDERLINE]="manUnderline", [ITALIC]="manItalic"}
+  local attr = NONE
+  local byte = 0 -- byte offset
+
+  local function end_attr_hl(attr)
+    for i, hl in ipairs(hls) do
+      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 continue_hl = true
+    if code == 0 then
+      attr = NONE
+      continue_hl = false
+    elseif code == 1 then
+      attr = BOLD
+    elseif code == 22 then
+      attr = BOLD
+      continue_hl = false
+    elseif code == 3 then
+      attr = ITALIC
+    elseif code == 23 then
+      attr = ITALIC
+      continue_hl = false
+    elseif code == 4 then
+      attr = UNDERLINE
+    elseif code == 24 then
+      attr = UNDERLINE
+      continue_hl = false
+    else
+      attr = NONE
+      return
+    end
+
+    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
+          end_attr_hl(a)
+        end
+      else
+        end_attr_hl(attr)
+      end
+    end
+  end
+
+  -- 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.final == byte then
+          -- This underscore is in the middle of an underlined word
+          attr = UNDERLINE
+        else
+          attr = BOLD
+        end
+      elseif prev_char == '_' then
+        -- char is underlined
+        attr = UNDERLINE
+      elseif prev_char == '+' and char == 'o' then
+        -- bullet (overstrike text '+^Ho')
+        attr = BOLD
+        char = '·'
+      elseif prev_char == '·' and char == 'o' then
+        -- bullet (additional handling for '+^H+^Ho^Ho')
+        attr = BOLD
+        char = '·'
+      else
+        -- use plain char
+        attr = NONE
+      end
+
+      -- Grow the previous highlight group if possible
+      if last_hl and last_hl.attr == attr and last_hl.final == byte then
+        last_hl.final = byte + #char
+      else
+        hls[#hls + 1] = {attr=attr, start=byte, final=byte + #char}
+      end
+
+      overstrike = false
+      prev_char = ''
+      byte = byte + #char
+      chars[#chars + 1] = char
+    elseif escape then
+      -- Use prev_char to store the escape sequence
+      prev_char = prev_char .. char
+      -- 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$")
+      if sgr then
+        local match = ''
+        while sgr and #sgr > 0 do
+          -- Match against SGR parameters, which may be separated by ';'
+          match, sgr = sgr:match("^(%d*);?(.*)")
+          add_attr_hl(match + 0) -- coerce to number
+        end
+        escape = false
+      elseif not prev_char:match("^%[[\032-\063]*$") then
+        -- Stop looking if this isn't a partial CSI sequence
+        escape = false
+      end
+    elseif char == "\027" then
+      escape = true
+      prev_char = ''
+    elseif char == "\b" then
+      overstrike = true
+      prev_char = chars[#chars]
+      byte = byte - #prev_char
+      chars[#chars] = nil
+    else
+      byte = byte + #char
+      chars[#chars + 1] = char
+    end
+  end
+
+  for _, hl in ipairs(hls) do
+    if hl.attr ~= NONE then
+      buf_hls[#buf_hls + 1] = {
+        0,
+        -1,
+        hl_groups[hl.attr],
+        linenr - 1,
+        hl.start,
+        hl.final
+      }
+    end
+  end
+
+  return table.concat(chars, '')
+end
+
+local function highlight_man_page()
+  local mod = vim.api.nvim_buf_get_option(0, "modifiable")
+  vim.api.nvim_buf_set_option(0, "modifiable", true)
+
+  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_buf_set_option(0, "modifiable", mod)
+end
+
+return { highlight_man_page = highlight_man_page }