feat: add support for diff and other filetypes

doc/diffs.nvim.txt

@@ -53,6 +53,7 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
     vim.g.diffs = {
       debug = false,
       hide_prefix = false,
+      filetypes = { 'fugitive', 'git', 'gitcommit' },
       highlights = {
         background = true,
         gutter = true,
@@ -115,6 +116,17 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              is also enabled, the overlay inherits the line's
                              background color.
 
+        {filetypes}          (table, default: {'fugitive','git','gitcommit'})
+                             List of filetypes that trigger attachment. Add
+                             `'diff'` to enable highlighting in plain `.diff`
+                             and `.patch` files: >lua
+                                 vim.g.diffs = {
+                                   filetypes = {
+                                     'fugitive', 'git', 'gitcommit', 'diff',
+                                   },
+                                 }
+<
+
         {highlights}         (table, default: see below)
                              Controls which highlight features are enabled.
                              See |diffs.Highlights| for fields.
@@ -588,8 +600,8 @@ refresh({bufnr})                                           *diffs.refresh()*
 IMPLEMENTATION                                        *diffs-implementation*
 
 Summary / commit detail views: ~
-1. `FileType fugitive` or `FileType git` (for `fugitive://` buffers)
-   triggers |diffs.attach()|
+1. `FileType` autocmd for configured filetypes (see {filetypes}) triggers
+   |diffs.attach()|. For `git` buffers, only `fugitive://` URIs are attached.
 2. The buffer is parsed to detect file headers (`M path/to/file`,
    `diff --git a/... b/...`) and hunk headers (`@@ -10,3 +10,4 @@`)
 3. For each hunk:

lua/diffs/init.lua

@@ -56,6 +56,7 @@
 ---@class diffs.Config
 ---@field debug boolean|string
 ---@field hide_prefix boolean
+---@field filetypes string[]
 ---@field highlights diffs.Highlights
 ---@field fugitive diffs.FugitiveConfig
 ---@field conflict diffs.ConflictConfig
@@ -107,6 +108,7 @@ end
 local default_config = {
   debug = false,
   hide_prefix = false,
+  filetypes = { 'fugitive', 'git', 'gitcommit' },
   highlights = {
     background = true,
     gutter = true,
@@ -402,6 +404,7 @@ local function init()
       'boolean or string (file path)',
     },
     hide_prefix = { opts.hide_prefix, 'boolean', true },
+    filetypes = { opts.filetypes, 'table', true },
     highlights = { opts.highlights, 'table', true },
   })
 

lua/diffs/parser.lua

@@ -151,6 +151,11 @@ function M.parse_buffer(bufnr)
   local file_new_start = nil
   ---@type integer?
   local file_new_count = nil
+  ---@type integer?
+  local old_remaining = nil
+  ---@type integer?
+  local new_remaining = nil
+  local is_unified_diff = false
 
   local function flush_hunk()
     if hunk_start and #hunk_lines > 0 then
@@ -183,11 +188,15 @@ function M.parse_buffer(bufnr)
     file_old_count = nil
     file_new_start = nil
     file_new_count = nil
+    old_remaining = nil
+    new_remaining = nil
   end
 
   for i, line in ipairs(lines) do
-    local filename = line:match('^[MADRCU%?!]%s+(.+)$') or line:match('^diff %-%-git a/.+ b/(.+)$')
+    local diff_git_file = line:match('^diff %-%-git a/.+ b/(.+)$')
+    local filename = line:match('^[MADRCU%?!]%s+(.+)$') or diff_git_file
     if filename then
+      is_unified_diff = diff_git_file ~= nil
       flush_hunk()
       current_filename = filename
       local cache_key = (repo_root or '') .. '\0' .. filename
@@ -223,6 +232,8 @@ function M.parse_buffer(bufnr)
           file_old_count = tonumber(hc) or 1
           file_new_start = tonumber(hs2)
           file_new_count = tonumber(hc2) or 1
+          old_remaining = file_old_count
+          new_remaining = file_new_count
         end
       else
         local hs2, hc2 = line:match('%+(%d+),?(%d*) @@')
@@ -243,6 +254,16 @@ function M.parse_buffer(bufnr)
       local prefix = line:sub(1, 1)
       if prefix == ' ' or prefix == '+' or prefix == '-' then
         table.insert(hunk_lines, line)
+        if old_remaining and (prefix == ' ' or prefix == '-') then
+          old_remaining = old_remaining - 1
+        end
+        if new_remaining and (prefix == ' ' or prefix == '+') then
+          new_remaining = new_remaining - 1
+        end
+      elseif line == '' and is_unified_diff and old_remaining and old_remaining > 0 and new_remaining and new_remaining > 0 then
+        table.insert(hunk_lines, ' ')
+        old_remaining = old_remaining - 1
+        new_remaining = new_remaining - 1
       elseif
         line == ''
         or line:match('^[MADRC%?!]%s+')

plugin/diffs.lua

@@ -6,7 +6,7 @@ vim.g.loaded_diffs = 1
 require('diffs.commands').setup()
 
 vim.api.nvim_create_autocmd('FileType', {
-  pattern = { 'fugitive', 'git', 'gitcommit' },
+  pattern = (vim.g.diffs or {}).filetypes or { 'fugitive', 'git', 'gitcommit' },
   callback = function(args)
     local diffs = require('diffs')
     if args.match == 'git' and not diffs.is_fugitive_buffer(args.buf) then