From 13c0ea1e9243cfa36649fc433b1bde594690d94a Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Wed, 4 Mar 2026 17:29:19 -0500
Subject: [PATCH 1/8] fix(highlight,parser,init): line_hl_group, clear_end,
 did_filetype, email-quoted diffs

Problem: line backgrounds used `hl_group + end_row` multirow extmarks
vulnerable to adjacent `clear_namespace`. `clear_end` was off by one.
`vim.filetype.match` returned nil for function-handled extensions
(`.sh`, `.bash`, etc.) when `did_filetype() != 0`. Parser didn't
handle email-quoted diff prefixes (`> `).

Solution: use `line_hl_group` single-point extmarks. Fix `clear_end`
to `hunk.start_line + #hunk.lines`. Override `vim.fn.did_filetype`
via `rawset` during retry. Strip `> ` quote prefixes in parser and
store `quote_width` per hunk.
---
 .styluaignore             |   1 +
 README.md                 |   1 +
 lua/diffs/highlight.lua   |  11 +-
 lua/diffs/init.lua        |   5 +-
 lua/diffs/parser.lua      |  81 +++++++++----
 spec/email_quote_spec.lua | 238 ++++++++++++++++++++++++++++++++++++++
 spec/highlight_spec.lua   | 128 ++++++++++++++++++--
 spec/integration_spec.lua | 118 +++++++++++++++++--
 spec/parser_spec.lua      |  21 ++++
 9 files changed, 552 insertions(+), 52 deletions(-)
 create mode 100644 .styluaignore
 create mode 100644 spec/email_quote_spec.lua

diff --git a/.styluaignore b/.styluaignore
new file mode 100644
index 0000000..9b42106
--- /dev/null
+++ b/.styluaignore
@@ -0,0 +1 @@
+.direnv/
diff --git a/README.md b/README.md
index 5d0022f..80fa968 100644
--- a/README.md
+++ b/README.md
@@ -17,6 +17,7 @@ with language-aware syntax highlighting.
 - `:Gdiff` unified diff against any revision
 - Background-only diff colors for `&diff` buffers
 - Inline merge conflict detection, highlighting, and resolution
+- Email-quoted diff highlighting (`> diff ...` prefixes, arbitrary nesting depth)
 - Vim syntax fallback, configurable blend/priorities
 
 ## Requirements
diff --git a/lua/diffs/highlight.lua b/lua/diffs/highlight.lua
index b31d630..541e6f9 100644
--- a/lua/diffs/highlight.lua
+++ b/lua/diffs/highlight.lua
@@ -496,17 +496,10 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
 
     if opts.highlights.background and is_diff_line then
       pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-        end_row = buf_line + 1,
-        hl_group = line_hl,
-        hl_eol = true,
+        line_hl_group = line_hl,
+        number_hl_group = opts.highlights.gutter and number_hl or nil,
         priority = p.line_bg,
       })
-      if opts.highlights.gutter then
-        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-          number_hl_group = number_hl,
-          priority = p.line_bg,
-        })
-      end
     end
 
     if is_marker and line_len > pw then
diff --git a/lua/diffs/init.lua b/lua/diffs/init.lua
index dcf05b6..e8d1f0d 100644
--- a/lua/diffs/init.lua
+++ b/lua/diffs/init.lua
@@ -765,7 +765,7 @@ local function init()
         if not entry.highlighted[i] then
           local hunk = entry.hunks[i]
           local clear_start = hunk.start_line - 1
-          local clear_end = clear_start + #hunk.lines
+          local clear_end = hunk.start_line + #hunk.lines
           if hunk.header_start_line then
             clear_start = hunk.header_start_line - 1
           end
@@ -799,7 +799,7 @@ local function init()
           }
           for _, hunk in ipairs(deferred_syntax) do
             local start_row = hunk.start_line - 1
-            local end_row = start_row + #hunk.lines
+            local end_row = hunk.start_line + #hunk.lines
             if hunk.header_start_line then
               start_row = hunk.header_start_line - 1
             end
@@ -953,6 +953,7 @@ M._test = {
   invalidate_cache = invalidate_cache,
   hunks_eq = hunks_eq,
   process_pending_clear = process_pending_clear,
+  ft_retry_pending = ft_retry_pending,
 }
 
 return M
diff --git a/lua/diffs/parser.lua b/lua/diffs/parser.lua
index fa1bcc0..4f657f3 100644
--- a/lua/diffs/parser.lua
+++ b/lua/diffs/parser.lua
@@ -13,6 +13,7 @@
 ---@field file_new_start integer?
 ---@field file_new_count integer?
 ---@field prefix_width integer
+---@field quote_width integer
 ---@field repo_root string?
 
 local M = {}
@@ -60,6 +61,13 @@ local function get_ft_from_filename(filename, repo_root)
   end
 
   local ft = vim.filetype.match({ filename = filename })
+  if not ft and vim.fn.did_filetype() ~= 0 then
+    dbg('retrying filetype match for %s (clearing did_filetype)', filename)
+    local saved = rawget(vim.fn, 'did_filetype')
+    rawset(vim.fn, 'did_filetype', function() return 0 end)
+    ft = vim.filetype.match({ filename = filename })
+    rawset(vim.fn, 'did_filetype', saved)
+  end
   if ft then
     dbg('filetype from filename: %s', ft)
     return ft
@@ -125,6 +133,18 @@ end
 function M.parse_buffer(bufnr)
   local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
   local repo_root = get_repo_root(bufnr)
+
+  local quote_prefix = nil
+  local quote_width = 0
+  for _, l in ipairs(lines) do
+    local qp = l:match('^(>+ )diff ') or l:match('^(>+ )@@')
+    if qp then
+      quote_prefix = qp
+      quote_width = #qp
+      break
+    end
+  end
+
   ---@type diffs.Hunk[]
   local hunks = {}
 
@@ -163,6 +183,7 @@ function M.parse_buffer(bufnr)
   ---@type integer?
   local new_remaining = nil
   local is_unified_diff = false
+  local current_quote_width = 0
 
   local function flush_hunk()
     if hunk_start and #hunk_lines > 0 then
@@ -175,6 +196,7 @@ function M.parse_buffer(bufnr)
         header_context_col = hunk_header_context_col,
         lines = hunk_lines,
         prefix_width = hunk_prefix_width,
+        quote_width = current_quote_width,
         file_old_start = file_old_start,
         file_old_count = file_old_count,
         file_new_start = file_new_start,
@@ -200,18 +222,31 @@ function M.parse_buffer(bufnr)
   end
 
   for i, line in ipairs(lines) do
-    local diff_git_file = line:match('^diff %-%-git a/.+ b/(.+)$')
-    local neogit_file = line:match('^modified%s+(.+)$')
-      or (not line:match('^new file mode') and line:match('^new file%s+(.+)$'))
-      or (not line:match('^deleted file mode') and line:match('^deleted%s+(.+)$'))
-      or line:match('^renamed%s+(.+)$')
-      or line:match('^copied%s+(.+)$')
-    local bare_file = not hunk_start and line:match('^([^%s]+%.[^%s]+)$')
-    local filename = line:match('^[MADRCU%?!]%s+(.+)$') or diff_git_file or neogit_file or bare_file
+    local logical = line
+    if quote_prefix then
+      if line:sub(1, quote_width) == quote_prefix then
+        logical = line:sub(quote_width + 1)
+      elseif line:match('^>+$') then
+        logical = ''
+      end
+    end
+
+    local diff_git_file = logical:match('^diff %-%-git a/.+ b/(.+)$')
+    local neogit_file = logical:match('^modified%s+(.+)$')
+      or (not logical:match('^new file mode') and logical:match('^new file%s+(.+)$'))
+      or (not logical:match('^deleted file mode') and logical:match('^deleted%s+(.+)$'))
+      or logical:match('^renamed%s+(.+)$')
+      or logical:match('^copied%s+(.+)$')
+    local bare_file = not hunk_start and logical:match('^([^%s]+%.[^%s]+)$')
+    local filename = logical:match('^[MADRCU%?!]%s+(.+)$')
+      or diff_git_file
+      or neogit_file
+      or bare_file
     if filename then
       is_unified_diff = diff_git_file ~= nil
       flush_hunk()
       current_filename = filename
+      current_quote_width = (logical ~= line) and quote_width or 0
       local cache_key = (repo_root or '') .. '\0' .. filename
       local cached = ft_lang_cache[cache_key]
       if cached then
@@ -233,13 +268,13 @@ function M.parse_buffer(bufnr)
       hunk_prefix_width = 1
       header_start = i
       header_lines = {}
-    elseif line:match('^@@+') then
+    elseif logical:match('^@@+') then
       flush_hunk()
       hunk_start = i
-      local at_prefix = line:match('^(@@+)')
+      local at_prefix = logical:match('^(@@+)')
       hunk_prefix_width = #at_prefix - 1
       if #at_prefix == 2 then
-        local hs, hc, hs2, hc2 = line:match('^@@ %-(%d+),?(%d*) %+(%d+),?(%d*) @@')
+        local hs, hc, hs2, hc2 = logical:match('^@@ %-(%d+),?(%d*) %+(%d+),?(%d*) @@')
         if hs then
           file_old_start = tonumber(hs)
           file_old_count = tonumber(hc) or 1
@@ -249,24 +284,24 @@ function M.parse_buffer(bufnr)
           new_remaining = file_new_count
         end
       else
-        local hs2, hc2 = line:match('%+(%d+),?(%d*) @@')
+        local hs2, hc2 = logical:match('%+(%d+),?(%d*) @@')
         if hs2 then
           file_new_start = tonumber(hs2)
           file_new_count = tonumber(hc2) or 1
         end
       end
-      local at_end, context = line:match('^(@@+.-@@+%s*)(.*)')
+      local at_end, context = logical:match('^(@@+.-@@+%s*)(.*)')
       if context and context ~= '' then
         hunk_header_context = context
-        hunk_header_context_col = #at_end
+        hunk_header_context_col = #at_end + current_quote_width
       end
       if hunk_count then
         hunk_count = hunk_count + 1
       end
     elseif hunk_start then
-      local prefix = line:sub(1, 1)
+      local prefix = logical:sub(1, 1)
       if prefix == ' ' or prefix == '+' or prefix == '-' then
-        table.insert(hunk_lines, line)
+        table.insert(hunk_lines, logical)
         if old_remaining and (prefix == ' ' or prefix == '-') then
           old_remaining = old_remaining - 1
         end
@@ -274,7 +309,7 @@ function M.parse_buffer(bufnr)
           new_remaining = new_remaining - 1
         end
       elseif
-        line == ''
+        logical == ''
         and is_unified_diff
         and old_remaining
         and old_remaining > 0
@@ -285,11 +320,11 @@ function M.parse_buffer(bufnr)
         old_remaining = old_remaining - 1
         new_remaining = new_remaining - 1
       elseif
-        line == ''
-        or line:match('^[MADRC%?!]%s+')
-        or line:match('^diff ')
-        or line:match('^index ')
-        or line:match('^Binary ')
+        logical == ''
+        or logical:match('^[MADRC%?!]%s+')
+        or logical:match('^diff ')
+        or logical:match('^index ')
+        or logical:match('^Binary ')
       then
         flush_hunk()
         current_filename = nil
@@ -299,7 +334,7 @@ function M.parse_buffer(bufnr)
       end
     end
     if header_start and not hunk_start then
-      table.insert(header_lines, line)
+      table.insert(header_lines, logical)
     end
   end
 
diff --git a/spec/email_quote_spec.lua b/spec/email_quote_spec.lua
new file mode 100644
index 0000000..fb445f6
--- /dev/null
+++ b/spec/email_quote_spec.lua
@@ -0,0 +1,238 @@
+require('spec.helpers')
+local parser = require('diffs.parser')
+local highlight = require('diffs.highlight')
+
+local function create_buffer(lines)
+  local bufnr = vim.api.nvim_create_buf(false, true)
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+  return bufnr
+end
+
+local function delete_buffer(bufnr)
+  if vim.api.nvim_buf_is_valid(bufnr) then
+    vim.api.nvim_buf_delete(bufnr, { force = true })
+  end
+end
+
+local function get_extmarks(bufnr, ns)
+  return vim.api.nvim_buf_get_extmarks(bufnr, ns, 0, -1, { details = true })
+end
+
+local function highlight_opts()
+  return {
+    hide_prefix = false,
+    highlights = {
+      background = true,
+      gutter = false,
+      context = { enabled = false, lines = 0 },
+      treesitter = { enabled = true, max_lines = 500 },
+      vim = { enabled = false, max_lines = 200 },
+      intra = { enabled = false, algorithm = 'default', max_lines = 500 },
+      priorities = { clear = 198, syntax = 199, line_bg = 200, char_bg = 201 },
+    },
+  }
+end
+
+describe('parser email-quoted diffs', function()
+
+  it('parses a fully email-quoted unified diff', function()
+    local bufnr = create_buffer({
+      '> diff --git a/foo.py b/foo.py',
+      '> index abc1234..def5678 100644',
+      '> --- a/foo.py',
+      '> +++ b/foo.py',
+      '> @@ -0,0 +1,3 @@',
+      '> +from typing import Annotated, final',
+      '> +',
+      '> +class Foo:',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal('foo.py', hunks[1].filename)
+    assert.are.equal(3, #hunks[1].lines)
+    assert.are.equal('+from typing import Annotated, final', hunks[1].lines[1])
+    assert.are.equal(2, hunks[1].quote_width)
+    delete_buffer(bufnr)
+  end)
+
+  it('parses a quoted diff embedded in an email reply', function()
+    local bufnr = create_buffer({
+      'Looks good, one nit:',
+      '',
+      '> diff --git a/foo.py b/foo.py',
+      '> @@ -0,0 +1,3 @@',
+      '> +from typing import Annotated, final',
+      '> +',
+      '> +class Foo:',
+      '',
+      'Maybe rename Foo to Bar?',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal('foo.py', hunks[1].filename)
+    assert.are.equal(3, #hunks[1].lines)
+    assert.are.equal(2, hunks[1].quote_width)
+    delete_buffer(bufnr)
+  end)
+
+  it('sets quote_width = 0 on normal (unquoted) diffs', function()
+    local bufnr = create_buffer({
+      'diff --git a/bar.lua b/bar.lua',
+      '@@ -1,2 +1,2 @@',
+      '-old_line',
+      '+new_line',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal(0, hunks[1].quote_width)
+    delete_buffer(bufnr)
+  end)
+
+  it('treats bare > lines as empty quoted lines', function()
+    local bufnr = create_buffer({
+      '> diff --git a/foo.py b/foo.py',
+      '> @@ -1,3 +1,3 @@',
+      '> -old',
+      '>',
+      '> +new',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal(3, #hunks[1].lines)
+    assert.are.equal('-old', hunks[1].lines[1])
+    assert.are.equal(' ', hunks[1].lines[2])
+    assert.are.equal('+new', hunks[1].lines[3])
+    delete_buffer(bufnr)
+  end)
+
+  it('adjusts header_context_col for quote width', function()
+    local bufnr = create_buffer({
+      '> diff --git a/foo.py b/foo.py',
+      '> @@ -1,2 +1,2 @@ def hello():',
+      '> -old',
+      '> +new',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal('def hello():', hunks[1].header_context)
+    assert.are.equal(#'@@ -1,2 +1,2 @@ ' + 2, hunks[1].header_context_col)
+    delete_buffer(bufnr)
+  end)
+
+  it('handles deeply nested quotes', function()
+    local bufnr = create_buffer({
+      '>> diff --git a/foo.py b/foo.py',
+      '>> @@ -0,0 +1,2 @@',
+      '>> +line1',
+      '>> +line2',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+
+    assert.are.equal(1, #hunks)
+    assert.are.equal(3, hunks[1].quote_width)
+    assert.are.equal('+line1', hunks[1].lines[1])
+    delete_buffer(bufnr)
+  end)
+end)
+
+describe('email-quoted header highlight suppression', function()
+  before_each(function()
+    vim.api.nvim_set_hl(0, 'DiffsClear', { fg = 0xc0c0c0, bg = 0x1e1e2e })
+    vim.api.nvim_set_hl(0, 'DiffsAdd', { bg = 0x2e4a3a })
+    vim.api.nvim_set_hl(0, 'DiffsDelete', { bg = 0x4a2e3a })
+  end)
+
+  it('applies DiffsClear to header lines when quote_width > 0', function()
+    local bufnr = create_buffer({
+      '> diff --git a/foo.py b/foo.py',
+      '> index abc1234..def5678 100644',
+      '> --- a/foo.py',
+      '> +++ b/foo.py',
+      '> @@ -0,0 +1,2 @@',
+      '> +line1',
+      '> +line2',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+    assert.are.equal(1, #hunks)
+
+    local ns = vim.api.nvim_create_namespace('diffs_email_clear_test')
+    highlight.highlight_hunk(bufnr, ns, hunks[1], highlight_opts())
+
+    local extmarks = get_extmarks(bufnr, ns)
+    local clear_lines = {}
+    for _, mark in ipairs(extmarks) do
+      local d = mark[4]
+      if d and d.hl_group == 'DiffsClear' and mark[3] == 0 then
+        clear_lines[mark[2]] = true
+      end
+    end
+    assert.is_true(clear_lines[0] ~= nil, 'expected DiffsClear on diff --git line')
+    assert.is_true(clear_lines[1] ~= nil, 'expected DiffsClear on index line')
+    assert.is_true(clear_lines[2] ~= nil, 'expected DiffsClear on --- line')
+    assert.is_true(clear_lines[3] ~= nil, 'expected DiffsClear on +++ line')
+    delete_buffer(bufnr)
+  end)
+
+  it('applies DiffsClear and diff treesitter to @@ line when quote_width > 0', function()
+    local bufnr = create_buffer({
+      '> diff --git a/foo.py b/foo.py',
+      '> @@ -0,0 +1,2 @@',
+      '> +line1',
+      '> +line2',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+    assert.are.equal(1, #hunks)
+
+    local ns = vim.api.nvim_create_namespace('diffs_email_at_test')
+    highlight.highlight_hunk(bufnr, ns, hunks[1], highlight_opts())
+
+    local extmarks = get_extmarks(bufnr, ns)
+    local has_at_clear = false
+    local has_at_ts = false
+    for _, mark in ipairs(extmarks) do
+      local d = mark[4]
+      if mark[2] == 1 and d then
+        if d.hl_group == 'DiffsClear' and mark[3] == 0 then
+          has_at_clear = true
+        end
+        if d.hl_group and d.hl_group:match('^@.*%.diff$') and d.priority == 199 then
+          has_at_ts = true
+        end
+      end
+    end
+    assert.is_true(has_at_clear, 'expected DiffsClear on @@ line')
+    assert.is_true(has_at_ts, 'expected diff treesitter capture on @@ line')
+    delete_buffer(bufnr)
+  end)
+
+  it('does not apply DiffsClear to header lines when quote_width = 0', function()
+    local bufnr = create_buffer({
+      'diff --git a/foo.py b/foo.py',
+      'index abc1234..def5678 100644',
+      '--- a/foo.py',
+      '+++ b/foo.py',
+      '@@ -0,0 +1,2 @@',
+      '+line1',
+      '+line2',
+    })
+    local hunks = parser.parse_buffer(bufnr)
+    assert.are.equal(1, #hunks)
+
+    local ns = vim.api.nvim_create_namespace('diffs_email_noclear_test')
+    highlight.highlight_hunk(bufnr, ns, hunks[1], highlight_opts())
+
+    local extmarks = get_extmarks(bufnr, ns)
+    for _, mark in ipairs(extmarks) do
+      local d = mark[4]
+      if d and d.hl_group == 'DiffsClear' and mark[3] == 0 and mark[2] < 5 then
+        error('unexpected DiffsClear at col 0 on header line ' .. mark[2] .. ' with quote_width=0')
+      end
+    end
+    delete_buffer(bufnr)
+  end)
+end)
diff --git a/spec/highlight_spec.lua b/spec/highlight_spec.lua
index 00a0774..2ba453f 100644
--- a/spec/highlight_spec.lua
+++ b/spec/highlight_spec.lua
@@ -287,7 +287,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -320,7 +320,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_diff_delete = true
           break
         end
@@ -362,6 +362,114 @@ describe('highlight', function()
       delete_buffer(bufnr)
     end)
 
+    it('line bg uses line_hl_group not hl_group with end_row', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+local y = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        assert.is_not_equal('DiffsAdd', d and d.hl_group)
+        assert.is_not_equal('DiffsDelete', d and d.hl_group)
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('line bg extmark survives adjacent clear_namespace starting at next row', function()
+      local bufnr = create_buffer({
+        'diff --git a/foo.py b/foo.py',
+        '@@ -1,2 +1,2 @@',
+        '-old',
+        '+new',
+      })
+
+      local hunk = {
+        filename = 'foo.py',
+        header_start_line = 1,
+        start_line = 2,
+        lines = { '-old', '+new' },
+        prefix_width = 1,
+        quote_width = 0,
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true, treesitter = { enabled = false } } })
+      )
+
+      local last_body_row = hunk.start_line + #hunk.lines - 1
+      vim.api.nvim_buf_clear_namespace(bufnr, ns, last_body_row + 1, last_body_row + 10)
+
+      local marks =
+        vim.api.nvim_buf_get_extmarks(bufnr, ns, { last_body_row, 0 }, { last_body_row, -1 }, { details = true })
+      local has_line_bg = false
+      for _, mark in ipairs(marks) do
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
+          has_line_bg = true
+        end
+      end
+      assert.is_true(has_line_bg)
+      delete_buffer(bufnr)
+    end)
+
+    it('clear range covers last body line of hunk with header', function()
+      local bufnr = create_buffer({
+        'diff --git a/foo.py b/foo.py',
+        'index abc..def 100644',
+        '--- a/foo.py',
+        '+++ b/foo.py',
+        '@@ -1,3 +1,3 @@',
+        ' ctx',
+        '-old',
+        '+new',
+      })
+
+      local hunk = {
+        filename = 'foo.py',
+        header_start_line = 1,
+        start_line = 5,
+        lines = { ' ctx', '-old', '+new' },
+        prefix_width = 1,
+        quote_width = 0,
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true, treesitter = { enabled = false } } })
+      )
+
+      local last_body_row = hunk.start_line + #hunk.lines - 1
+      local clear_start = hunk.header_start_line - 1
+      local clear_end = hunk.start_line + #hunk.lines
+      vim.api.nvim_buf_clear_namespace(bufnr, ns, clear_start, clear_end)
+
+      local marks =
+        vim.api.nvim_buf_get_extmarks(bufnr, ns, { last_body_row, 0 }, { last_body_row, -1 }, { details = false })
+      assert.are.equal(0, #marks)
+      delete_buffer(bufnr)
+    end)
+
     it('still applies background when treesitter disabled', function()
       local bufnr = create_buffer({
         '@@ -1,1 +1,2 @@',
@@ -386,7 +494,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -500,7 +608,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -585,7 +693,7 @@ describe('highlight', function()
       local found = false
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
           found = true
         end
       end
@@ -741,7 +849,7 @@ describe('highlight', function()
         if d then
           if d.hl_group == 'DiffsClear' then
             table.insert(priorities.clear, d.priority)
-          elseif (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+          elseif (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
             table.insert(priorities.line_bg, d.priority)
           elseif d.hl_group == 'DiffsAddText' or d.hl_group == 'DiffsDeleteText' then
             table.insert(priorities.char_bg, d.priority)
@@ -842,8 +950,8 @@ describe('highlight', function()
       local line_bgs = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
-          line_bgs[mark[2]] = d.hl_group
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
+          line_bgs[mark[2]] = d.line_hl_group
         end
       end
       assert.is_nil(line_bgs[1])
@@ -1034,8 +1142,8 @@ describe('highlight', function()
       local marker_text = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
-          line_bgs[mark[2]] = d.hl_group
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
+          line_bgs[mark[2]] = d.line_hl_group
         end
         if d and d.number_hl_group then
           gutter_hls[mark[2]] = d.number_hl_group
diff --git a/spec/integration_spec.lua b/spec/integration_spec.lua
index 7468e8f..fe221c0 100644
--- a/spec/integration_spec.lua
+++ b/spec/integration_spec.lua
@@ -127,6 +127,108 @@ describe('integration', function()
     end)
   end)
 
+  describe('ft_retry_pending', function()
+    before_each(function()
+      rawset(vim.fn, 'did_filetype', function() return 1 end)
+      require('diffs.parser')._test.ft_lang_cache = {}
+    end)
+
+    after_each(function()
+      rawset(vim.fn, 'did_filetype', nil)
+    end)
+
+    it('sets ft_retry_pending when nil-ft hunks detected under did_filetype', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      local entry = diffs._test.hunk_cache[bufnr]
+      assert.is_not_nil(entry)
+      assert.is_nil(entry.hunks[1].ft)
+      assert.is_true(diffs._test.ft_retry_pending[bufnr] == true)
+      delete_buffer(bufnr)
+    end)
+
+    it('clears ft_retry_pending after scheduled callback fires', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      assert.is_true(diffs._test.ft_retry_pending[bufnr] == true)
+
+      local done = false
+      vim.schedule(function()
+        done = true
+      end)
+      vim.wait(1000, function()
+        return done
+      end)
+
+      assert.is_nil(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+
+    it('invalidates cache after scheduled callback fires', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      local tick_after_attach = diffs._test.hunk_cache[bufnr].tick
+      assert.is_true(tick_after_attach >= 0)
+
+      local done = false
+      vim.schedule(function()
+        done = true
+      end)
+      vim.wait(1000, function()
+        return done
+      end)
+
+      local entry = diffs._test.hunk_cache[bufnr]
+      assert.are.equal(-1, entry.tick)
+      assert.is_true(entry.pending_clear)
+      delete_buffer(bufnr)
+    end)
+
+    it('does not set ft_retry_pending when did_filetype() is zero', function()
+      rawset(vim.fn, 'did_filetype', nil)
+      local bufnr = create_buffer({
+        'diff --git a/test.sh b/test.sh',
+        '@@ -1,2 +1,3 @@',
+        ' #!/usr/bin/env bash',
+        '-old line',
+        '+new line',
+      })
+      diffs.attach(bufnr)
+      assert.is_falsy(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+
+    it('does not set ft_retry_pending for files with resolvable ft', function()
+      local bufnr = create_buffer({
+        'M test.lua',
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+local y = 2',
+      })
+      diffs.attach(bufnr)
+      assert.is_falsy(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+  end)
+
   describe('extmarks from highlight pipeline', function()
     it('DiffsAdd background applied to + lines', function()
       local bufnr = create_buffer({
@@ -145,7 +247,7 @@ describe('integration', function()
       local extmarks = get_extmarks(bufnr, ns)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -171,7 +273,7 @@ describe('integration', function()
       local extmarks = get_extmarks(bufnr, ns)
       local has_diff_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_diff_delete = true
           break
         end
@@ -198,10 +300,10 @@ describe('integration', function()
       local has_add = false
       local has_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_add = true
         end
-        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_delete = true
         end
       end
@@ -230,8 +332,8 @@ describe('integration', function()
       local line_bgs = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
-          line_bgs[mark[2]] = d.hl_group
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
+          line_bgs[mark[2]] = d.line_hl_group
         end
       end
       assert.is_nil(line_bgs[1])
@@ -313,10 +415,10 @@ describe('integration', function()
       local del_lines = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and d.hl_group == 'DiffsAdd' and d.hl_eol then
+        if d and d.line_hl_group == 'DiffsAdd' then
           add_lines[mark[2]] = true
         end
-        if d and d.hl_group == 'DiffsDelete' and d.hl_eol then
+        if d and d.line_hl_group == 'DiffsDelete' then
           del_lines[mark[2]] = true
         end
       end
diff --git a/spec/parser_spec.lua b/spec/parser_spec.lua
index 5613784..f084fbc 100644
--- a/spec/parser_spec.lua
+++ b/spec/parser_spec.lua
@@ -391,6 +391,27 @@ describe('parser', function()
       vim.fn.delete(repo_root, 'rf')
     end)
 
+    it('detects filetype for .sh files when did_filetype() is non-zero', function()
+      rawset(vim.fn, 'did_filetype', function() return 1 end)
+
+      parser._test.ft_lang_cache = {}
+      local bufnr = create_buffer({
+        'diff --git a/test.sh b/test.sh',
+        '@@ -1,3 +1,4 @@',
+        ' #!/usr/bin/env bash',
+        ' set -euo pipefail',
+        '-echo "running tests..."',
+        '+echo "running tests with coverage..."',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('test.sh', hunks[1].filename)
+      assert.are.equal('sh', hunks[1].ft)
+      delete_buffer(bufnr)
+      rawset(vim.fn, 'did_filetype', nil)
+    end)
+
     it('extracts file line numbers from @@ header', function()
       local bufnr = create_buffer({
         'M lua/test.lua',

From e5d9b4b7bd034abaa5bdbadd9a38c33ebe840657 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Wed, 4 Mar 2026 17:32:55 -0500
Subject: [PATCH 2/8] ci: formatting

---
 .luarc.json               |  7 ++++++-
 README.md                 |  3 ++-
 lua/diffs/highlight.lua   | 11 ++++++-----
 lua/diffs/init.lua        |  6 +++++-
 lua/diffs/parser.lua      |  4 +++-
 spec/email_quote_spec.lua |  3 +--
 spec/highlight_spec.lua   | 20 +++++++++++++++-----
 spec/integration_spec.lua |  4 +++-
 spec/parser_spec.lua      |  4 +++-
 9 files changed, 44 insertions(+), 18 deletions(-)

diff --git a/.luarc.json b/.luarc.json
index eb18f65..3f6276a 100644
--- a/.luarc.json
+++ b/.luarc.json
@@ -2,7 +2,12 @@
   "runtime.version": "LuaJIT",
   "runtime.path": ["lua/?.lua", "lua/?/init.lua"],
   "diagnostics.globals": ["vim", "jit"],
-  "workspace.library": ["$VIMRUNTIME/lua", "${3rd}/luv/library", "${3rd}/busted/library", "${3rd}/luassert/library"],
+  "workspace.library": [
+    "$VIMRUNTIME/lua",
+    "${3rd}/luv/library",
+    "${3rd}/busted/library",
+    "${3rd}/luassert/library"
+  ],
   "workspace.checkThirdParty": false,
   "workspace.ignoreDir": [".direnv"],
   "completion.callSnippet": "Replace"
diff --git a/README.md b/README.md
index 80fa968..eee728d 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,8 @@ with language-aware syntax highlighting.
 - `:Gdiff` unified diff against any revision
 - Background-only diff colors for `&diff` buffers
 - Inline merge conflict detection, highlighting, and resolution
-- Email-quoted diff highlighting (`> diff ...` prefixes, arbitrary nesting depth)
+- Email-quoted diff highlighting (`> diff ...` prefixes, arbitrary nesting
+  depth)
 - Vim syntax fallback, configurable blend/priorities
 
 ## Requirements
diff --git a/lua/diffs/highlight.lua b/lua/diffs/highlight.lua
index 541e6f9..98943d2 100644
--- a/lua/diffs/highlight.lua
+++ b/lua/diffs/highlight.lua
@@ -522,11 +522,12 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
           char_hl,
           line:sub(span.col_start + 1, span.col_end)
         )
-        local ok, err = pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start + qw, {
-          end_col = span.col_end + qw,
-          hl_group = char_hl,
-          priority = p.char_bg,
-        })
+        local ok, err =
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start + qw, {
+            end_col = span.col_end + qw,
+            hl_group = char_hl,
+            priority = p.char_bg,
+          })
         if not ok then
           dbg('char extmark FAILED: %s', err)
         end
diff --git a/lua/diffs/init.lua b/lua/diffs/init.lua
index e8d1f0d..6af7e1a 100644
--- a/lua/diffs/init.lua
+++ b/lua/diffs/init.lua
@@ -789,7 +789,11 @@ local function init()
           end
           local cur = hunk_cache[bufnr]
           if not cur or cur.tick ~= tick then
-            dbg('deferred syntax stale: cur.tick=%s captured=%d', cur and tostring(cur.tick) or 'nil', tick)
+            dbg(
+              'deferred syntax stale: cur.tick=%s captured=%d',
+              cur and tostring(cur.tick) or 'nil',
+              tick
+            )
             return
           end
           local t1 = config.debug and vim.uv.hrtime() or nil
diff --git a/lua/diffs/parser.lua b/lua/diffs/parser.lua
index 4f657f3..4490c90 100644
--- a/lua/diffs/parser.lua
+++ b/lua/diffs/parser.lua
@@ -64,7 +64,9 @@ local function get_ft_from_filename(filename, repo_root)
   if not ft and vim.fn.did_filetype() ~= 0 then
     dbg('retrying filetype match for %s (clearing did_filetype)', filename)
     local saved = rawget(vim.fn, 'did_filetype')
-    rawset(vim.fn, 'did_filetype', function() return 0 end)
+    rawset(vim.fn, 'did_filetype', function()
+      return 0
+    end)
     ft = vim.filetype.match({ filename = filename })
     rawset(vim.fn, 'did_filetype', saved)
   end
diff --git a/spec/email_quote_spec.lua b/spec/email_quote_spec.lua
index fb445f6..3f2bd6e 100644
--- a/spec/email_quote_spec.lua
+++ b/spec/email_quote_spec.lua
@@ -1,6 +1,6 @@
 require('spec.helpers')
-local parser = require('diffs.parser')
 local highlight = require('diffs.highlight')
+local parser = require('diffs.parser')
 
 local function create_buffer(lines)
   local bufnr = vim.api.nvim_create_buf(false, true)
@@ -34,7 +34,6 @@ local function highlight_opts()
 end
 
 describe('parser email-quoted diffs', function()
-
   it('parses a fully email-quoted unified diff', function()
     local bufnr = create_buffer({
       '> diff --git a/foo.py b/foo.py',
diff --git a/spec/highlight_spec.lua b/spec/highlight_spec.lua
index 2ba453f..ebd075f 100644
--- a/spec/highlight_spec.lua
+++ b/spec/highlight_spec.lua
@@ -419,8 +419,13 @@ describe('highlight', function()
       local last_body_row = hunk.start_line + #hunk.lines - 1
       vim.api.nvim_buf_clear_namespace(bufnr, ns, last_body_row + 1, last_body_row + 10)
 
-      local marks =
-        vim.api.nvim_buf_get_extmarks(bufnr, ns, { last_body_row, 0 }, { last_body_row, -1 }, { details = true })
+      local marks = vim.api.nvim_buf_get_extmarks(
+        bufnr,
+        ns,
+        { last_body_row, 0 },
+        { last_body_row, -1 },
+        { details = true }
+      )
       local has_line_bg = false
       for _, mark in ipairs(marks) do
         if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
@@ -464,8 +469,13 @@ describe('highlight', function()
       local clear_end = hunk.start_line + #hunk.lines
       vim.api.nvim_buf_clear_namespace(bufnr, ns, clear_start, clear_end)
 
-      local marks =
-        vim.api.nvim_buf_get_extmarks(bufnr, ns, { last_body_row, 0 }, { last_body_row, -1 }, { details = false })
+      local marks = vim.api.nvim_buf_get_extmarks(
+        bufnr,
+        ns,
+        { last_body_row, 0 },
+        { last_body_row, -1 },
+        { details = false }
+      )
       assert.are.equal(0, #marks)
       delete_buffer(bufnr)
     end)
@@ -849,7 +859,7 @@ describe('highlight', function()
         if d then
           if d.hl_group == 'DiffsClear' then
             table.insert(priorities.clear, d.priority)
-          elseif (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
+          elseif d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete' then
             table.insert(priorities.line_bg, d.priority)
           elseif d.hl_group == 'DiffsAddText' or d.hl_group == 'DiffsDeleteText' then
             table.insert(priorities.char_bg, d.priority)
diff --git a/spec/integration_spec.lua b/spec/integration_spec.lua
index fe221c0..23e870b 100644
--- a/spec/integration_spec.lua
+++ b/spec/integration_spec.lua
@@ -129,7 +129,9 @@ describe('integration', function()
 
   describe('ft_retry_pending', function()
     before_each(function()
-      rawset(vim.fn, 'did_filetype', function() return 1 end)
+      rawset(vim.fn, 'did_filetype', function()
+        return 1
+      end)
       require('diffs.parser')._test.ft_lang_cache = {}
     end)
 
diff --git a/spec/parser_spec.lua b/spec/parser_spec.lua
index f084fbc..729ad16 100644
--- a/spec/parser_spec.lua
+++ b/spec/parser_spec.lua
@@ -392,7 +392,9 @@ describe('parser', function()
     end)
 
     it('detects filetype for .sh files when did_filetype() is non-zero', function()
-      rawset(vim.fn, 'did_filetype', function() return 1 end)
+      rawset(vim.fn, 'did_filetype', function()
+        return 1
+      end)
 
       parser._test.ft_lang_cache = {}
       local bufnr = create_buffer({

From 194f29159a1d19f57484d4b6a1ceb599333086c3 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Wed, 4 Mar 2026 17:33:31 -0500
Subject: [PATCH 3/8] fix: format

---
 flake.nix | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/flake.nix b/flake.nix
index 38e98cd..2221bdf 100644
--- a/flake.nix
+++ b/flake.nix
@@ -13,7 +13,8 @@
       ...
     }:
     let
-      forEachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
+      forEachSystem =
+        f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
     in
     {
       formatter = forEachSystem (pkgs: pkgs.nixfmt-tree);
@@ -23,7 +24,12 @@
           let
             ts-plugin = pkgs.vimPlugins.nvim-treesitter.withPlugins (p: [ p.diff ]);
             diff-grammar = pkgs.vimPlugins.nvim-treesitter-parsers.diff;
-            luaEnv = pkgs.luajit.withPackages (ps: with ps; [ busted nlua ]);
+            luaEnv = pkgs.luajit.withPackages (
+              ps: with ps; [
+                busted
+                nlua
+              ]
+            );
             busted-with-grammar = pkgs.writeShellScriptBin "busted" ''
               nvim_bin=$(which nvim)
               tmpdir=$(mktemp -d)
@@ -34,14 +40,14 @@
             '';
           in
           pkgs.mkShell {
-          packages = [
-            busted-with-grammar
-            pkgs.prettier
-            pkgs.stylua
-            pkgs.selene
-            pkgs.lua-language-server
-          ];
-        };
+            packages = [
+              busted-with-grammar
+              pkgs.prettier
+              pkgs.stylua
+              pkgs.selene
+              pkgs.lua-language-server
+            ];
+          };
       });
     };
 }

From 38e018799859d8aeb504fae29ea503f7bf456aa2 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Thu, 5 Mar 2026 01:06:27 -0500
Subject: [PATCH 4/8] ci: disable library file diagnostics in `.luarc.json`

---
 .luarc.json | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.luarc.json b/.luarc.json
index 3f6276a..bfbf500 100644
--- a/.luarc.json
+++ b/.luarc.json
@@ -9,6 +9,7 @@
     "${3rd}/luassert/library"
   ],
   "workspace.checkThirdParty": false,
+  "diagnostics.libraryFiles": "Disable",
   "workspace.ignoreDir": [".direnv"],
   "completion.callSnippet": "Replace"
 }

From bb87ae279b9d69a626505b1ae9581aaa8a74a34a Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Thu, 5 Mar 2026 01:06:37 -0500
Subject: [PATCH 5/8] feat(parser): support combined diff format

Problem: `parse_buffer` didn't recognize `diff --combined` /
`diff --cc` headers, couldn't parse `@@@` old-side ranges, and
synthesized empty body lines as single-space regardless of prefix
width.

Solution: Add `diff --combined` and `diff --cc` filename patterns,
parse old-side `-start,count` from `@@@` lines, remove
`is_unified_diff` guard on empty body lines, and use
`string.rep(' ', hunk_prefix_width)` for synthetic context lines.
---
 lua/diffs/parser.lua | 12 ++++++++++--
 spec/parser_spec.lua |  7 ++++---
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/lua/diffs/parser.lua b/lua/diffs/parser.lua
index 4490c90..2ef3030 100644
--- a/lua/diffs/parser.lua
+++ b/lua/diffs/parser.lua
@@ -234,6 +234,8 @@ function M.parse_buffer(bufnr)
     end
 
     local diff_git_file = logical:match('^diff %-%-git a/.+ b/(.+)$')
+      or logical:match('^diff %-%-combined (.+)$')
+      or logical:match('^diff %-%-cc (.+)$')
     local neogit_file = logical:match('^modified%s+(.+)$')
       or (not logical:match('^new file mode') and logical:match('^new file%s+(.+)$'))
       or (not logical:match('^deleted file mode') and logical:match('^deleted%s+(.+)$'))
@@ -286,10 +288,17 @@ function M.parse_buffer(bufnr)
           new_remaining = file_new_count
         end
       else
+        local hs, hc = logical:match('%-(%d+),?(%d*)')
+        if hs then
+          file_old_start = tonumber(hs)
+          file_old_count = tonumber(hc) or 1
+          old_remaining = file_old_count
+        end
         local hs2, hc2 = logical:match('%+(%d+),?(%d*) @@')
         if hs2 then
           file_new_start = tonumber(hs2)
           file_new_count = tonumber(hc2) or 1
+          new_remaining = file_new_count
         end
       end
       local at_end, context = logical:match('^(@@+.-@@+%s*)(.*)')
@@ -312,13 +321,12 @@ function M.parse_buffer(bufnr)
         end
       elseif
         logical == ''
-        and is_unified_diff
         and old_remaining
         and old_remaining > 0
         and new_remaining
         and new_remaining > 0
       then
-        table.insert(hunk_lines, ' ')
+        table.insert(hunk_lines, string.rep(' ', hunk_prefix_width))
         old_remaining = old_remaining - 1
         new_remaining = new_remaining - 1
       elseif
diff --git a/spec/parser_spec.lua b/spec/parser_spec.lua
index 729ad16..adbbd37 100644
--- a/spec/parser_spec.lua
+++ b/spec/parser_spec.lua
@@ -163,10 +163,10 @@ describe('parser', function()
       end
     end)
 
-    it('stops hunk at blank line', function()
+    it('stops hunk at blank line when remaining counts exhausted', function()
       local bufnr = create_buffer({
         'M test.lua',
-        '@@ -1,2 +1,3 @@',
+        '@@ -1,1 +1,2 @@',
         ' local x = 1',
         '+local y = 2',
         '',
@@ -529,7 +529,8 @@ describe('parser', function()
       assert.are.equal(1, #hunks)
       assert.are.equal(1, hunks[1].file_new_start)
       assert.are.equal(9, hunks[1].file_new_count)
-      assert.is_nil(hunks[1].file_old_start)
+      assert.are.equal(1, hunks[1].file_old_start)
+      assert.are.equal(3, hunks[1].file_old_count)
       delete_buffer(bufnr)
     end)
 

From d2921c6fdd90c925a4743018b08bc18ad09fa064 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Thu, 5 Mar 2026 01:06:51 -0500
Subject: [PATCH 6/8] feat(highlight): support combined diff highlighting

Problem: Combined diffs (`pw > 1`) had no DiffsClear on headers
or `@@@`, no per-char prefix coloring, native TS junk on body
prefixes, and `force_high_priority` flattened all diff captures
to p199 making `@punctuation.special` (cyan) win over
`@diff.minus`/`@diff.plus` (red/green) on `---`/`+++` lines. The
`index` keyword and result hash after `..` were also uncolored.

Solution: Extend `qw > 0` guards to `qw > 0 or pw > 1` for
headers, `@@@`, and body prefixes. Add per-char `@diff.plus` /
`@diff.minus` at p199 on body prefix columns. Apply
`@attribute.diff` on `@@@` lines. Preserve relative priority
offsets in `highlight_treesitter` via `priorities.syntax +
meta_prio - 100`. Add manual `@keyword.diff` and `@constant.diff`
captures on combined `index` lines.
---
 lua/diffs/highlight.lua |  66 +++++-
 spec/highlight_spec.lua | 450 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 508 insertions(+), 8 deletions(-)

diff --git a/lua/diffs/highlight.lua b/lua/diffs/highlight.lua
index 98943d2..2a2f8b1 100644
--- a/lua/diffs/highlight.lua
+++ b/lua/diffs/highlight.lua
@@ -74,6 +74,7 @@ end
 ---@param col_offset integer
 ---@param covered_lines? table<integer, true>
 ---@param priorities diffs.PrioritiesConfig
+---@param force_high_priority? boolean
 ---@return integer
 local function highlight_treesitter(
   bufnr,
@@ -83,7 +84,8 @@ local function highlight_treesitter(
   line_map,
   col_offset,
   covered_lines,
-  priorities
+  priorities,
+  force_high_priority
 )
   local code = table.concat(code_lines, '\n')
   if code == '' then
@@ -123,8 +125,9 @@ local function highlight_treesitter(
           local buf_sc = sc + col_offset
           local buf_ec = ec + col_offset
 
+          local meta_prio = tonumber(metadata.priority) or 100
           local priority = tree_lang == 'diff'
-              and (col_offset > 0 and priorities.syntax or (tonumber(metadata.priority) or 100))
+              and ((col_offset > 0 or force_high_priority) and (priorities.syntax + meta_prio - 100) or meta_prio)
             or priorities.syntax
 
           pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
@@ -367,14 +370,14 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       header_map[i] = hunk.header_start_line - 1 + i
     end
     extmark_count = extmark_count
-      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, qw, nil, p)
+      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, qw, nil, p, qw > 0 or pw > 1)
   end
 
   local at_raw_line
-  if qw > 0 and opts.highlights.treesitter.enabled then
+  if (qw > 0 or pw > 1) and opts.highlights.treesitter.enabled then
     local at_buf_line = hunk.start_line - 1
     at_raw_line = vim.api.nvim_buf_get_lines(bufnr, at_buf_line, at_buf_line + 1, false)[1]
-    if at_raw_line then
+    if qw > 0 and at_raw_line then
       local at_logical = at_raw_line:sub(qw + 1)
       local at_map = { [0] = at_buf_line }
       extmark_count = extmark_count
@@ -417,7 +420,7 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
   end
 
   if
-    qw > 0
+    (qw > 0 or pw > 1)
     and hunk.header_start_line
     and hunk.header_lines
     and #hunk.header_lines > 0
@@ -430,16 +433,46 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
         hl_group = 'DiffsClear',
         priority = p.clear,
       })
+
+      if pw > 1 then
+        local hline = hunk.header_lines[i + 1]
+        if hline:match('^index ') then
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, qw, {
+            end_col = qw + 5,
+            hl_group = '@keyword.diff',
+            priority = p.syntax,
+          })
+          local dot_pos = hline:find('%.%.', 1, false)
+          if dot_pos then
+            local rest = hline:sub(dot_pos + 2)
+            local hash = rest:match('^(%x+)')
+            if hash then
+              pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, qw + dot_pos + 1, {
+                end_col = qw + dot_pos + 1 + #hash,
+                hl_group = '@constant.diff',
+                priority = p.syntax,
+              })
+            end
+          end
+        end
+      end
     end
   end
 
-  if qw > 0 and at_raw_line then
+  if (qw > 0 or pw > 1) and at_raw_line then
     local at_buf_line = hunk.start_line - 1
     pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, at_buf_line, 0, {
       end_col = #at_raw_line,
       hl_group = 'DiffsClear',
       priority = p.clear,
     })
+    if pw > 1 and opts.highlights.treesitter.enabled then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, at_buf_line, qw, {
+        end_col = #at_raw_line,
+        hl_group = '@attribute.diff',
+        priority = p.syntax,
+      })
+    end
   end
 
   if use_ts and hunk.header_context and hunk.header_context_col then
@@ -484,6 +517,25 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
         hl_group = 'DiffsClear',
         priority = p.clear,
       })
+    elseif pw > 1 then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+        end_col = pw,
+        hl_group = 'DiffsClear',
+        priority = p.clear,
+      })
+    end
+
+    if pw > 1 then
+      for ci = 0, pw - 1 do
+        local ch = line:sub(ci + 1, ci + 1)
+        if ch == '+' or ch == '-' then
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, ci + qw, {
+            end_col = ci + qw + 1,
+            hl_group = ch == '+' and '@diff.plus' or '@diff.minus',
+            priority = p.syntax,
+          })
+        end
+      end
     end
 
     if line_len > pw and covered_lines[buf_line] then
diff --git a/spec/highlight_spec.lua b/spec/highlight_spec.lua
index ebd075f..4695d66 100644
--- a/spec/highlight_spec.lua
+++ b/spec/highlight_spec.lua
@@ -1064,11 +1064,16 @@ describe('highlight', function()
       highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
 
       local extmarks = get_extmarks(bufnr)
+      local content_clear_count = 0
       for _, mark in ipairs(extmarks) do
         if mark[4] and mark[4].hl_group == 'DiffsClear' then
-          assert.are.equal(2, mark[3])
+          assert.is_true(mark[3] == 0 or mark[3] == 2, 'DiffsClear at unexpected col ' .. mark[3])
+          if mark[3] == 2 then
+            content_clear_count = content_clear_count + 1
+          end
         end
       end
+      assert.are.equal(2, content_clear_count)
       delete_buffer(bufnr)
     end)
 
@@ -1363,6 +1368,449 @@ describe('highlight', function()
       assert.are.equal(0, header_extmarks)
       delete_buffer(bufnr)
     end)
+
+    it('does not apply DiffsClear to header lines for non-quoted diffs', function()
+      local bufnr = create_buffer({
+        'diff --git a/parser.lua b/parser.lua',
+        'index 3e8afa0..018159c 100644',
+        '--- a/parser.lua',
+        '+++ b/parser.lua',
+        '@@ -1,2 +1,3 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+
+      local hunk = {
+        filename = 'parser.lua',
+        lang = 'lua',
+        start_line = 5,
+        lines = { ' local M = {}', '+local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --git a/parser.lua b/parser.lua',
+          'index 3e8afa0..018159c 100644',
+          '--- a/parser.lua',
+          '+++ b/parser.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsClear' and mark[3] == 0 and mark[2] < 4 then
+          error('unexpected DiffsClear on header row ' .. mark[2] .. ' for non-quoted diff')
+        end
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('preserves diff grammar treesitter on headers for non-quoted diffs', function()
+      local bufnr = create_buffer({
+        'diff --git a/parser.lua b/parser.lua',
+        '--- a/parser.lua',
+        '+++ b/parser.lua',
+        '@@ -1,2 +1,3 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+
+      local hunk = {
+        filename = 'parser.lua',
+        lang = 'lua',
+        start_line = 4,
+        lines = { ' local M = {}', '+local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --git a/parser.lua b/parser.lua',
+          '--- a/parser.lua',
+          '+++ b/parser.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local header_ts_count = 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] < 3 and d and d.hl_group and d.hl_group:match('^@.*%.diff$') then
+          header_ts_count = header_ts_count + 1
+        end
+      end
+      assert.is_true(header_ts_count > 0, 'expected diff grammar treesitter on header lines')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies syntax extmarks to combined diff body lines', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+        ' -local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1', ' -local y = 2' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local syntax_on_body = 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] >= 1 and d and d.hl_group and d.hl_group:match('^@.*%.lua$') then
+          syntax_on_body = syntax_on_body + 1
+        end
+      end
+      assert.is_true(syntax_on_body > 0, 'expected lua treesitter syntax on combined diff body')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear and per-char diff fg to combined diff body prefixes', function()
+      local bufnr = create_buffer({
+        '@@@',
+        '  unchanged',
+        '+ added',
+        ' -removed',
+        '++both',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  unchanged', '+ added', ' -removed', '++both' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local prefix_clears = {}
+      local plus_marks = {}
+      local minus_marks = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] >= 1 and d then
+          if d.hl_group == 'DiffsClear' and mark[3] == 0 and d.end_col == 2 then
+            prefix_clears[mark[2]] = true
+          end
+          if d.hl_group == '@diff.plus' and d.priority == 199 then
+            if not plus_marks[mark[2]] then
+              plus_marks[mark[2]] = {}
+            end
+            table.insert(plus_marks[mark[2]], mark[3])
+          end
+          if d.hl_group == '@diff.minus' and d.priority == 199 then
+            if not minus_marks[mark[2]] then
+              minus_marks[mark[2]] = {}
+            end
+            table.insert(minus_marks[mark[2]], mark[3])
+          end
+        end
+      end
+
+      assert.is_true(prefix_clears[1] ~= nil, 'DiffsClear on context prefix')
+      assert.is_true(prefix_clears[2] ~= nil, 'DiffsClear on add prefix')
+      assert.is_true(prefix_clears[3] ~= nil, 'DiffsClear on del prefix')
+      assert.is_true(prefix_clears[4] ~= nil, 'DiffsClear on both-add prefix')
+
+      assert.is_true(plus_marks[2] ~= nil, '@diff.plus on + in "+ added"')
+      assert.are.equal(0, plus_marks[2][1])
+
+      assert.is_true(minus_marks[3] ~= nil, '@diff.minus on - in " -removed"')
+      assert.are.equal(1, minus_marks[3][1])
+
+      assert.is_true(plus_marks[4] ~= nil, '@diff.plus on ++ in "++both"')
+      assert.are.equal(2, #plus_marks[4])
+
+      assert.is_nil(plus_marks[1], 'no @diff.plus on context "  unchanged"')
+      assert.is_nil(minus_marks[1], 'no @diff.minus on context "  unchanged"')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear to headers for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local clear_lines = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsClear' and mark[3] == 0 and mark[2] < 4 then
+          clear_lines[mark[2]] = true
+        end
+      end
+      assert.is_true(clear_lines[0] ~= nil, 'DiffsClear on diff --combined line')
+      assert.is_true(clear_lines[1] ~= nil, 'DiffsClear on index line')
+      assert.is_true(clear_lines[2] ~= nil, 'DiffsClear on --- line')
+      assert.is_true(clear_lines[3] ~= nil, 'DiffsClear on +++ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @attribute.diff at syntax priority to @@@ line for combined diffs', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_attr = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 0 and d and d.hl_group == '@attribute.diff' and (d.priority or 0) >= 199 then
+          has_attr = true
+        end
+      end
+      assert.is_true(has_attr, '@attribute.diff at p>=199 on @@@ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear to @@@ line for combined diffs', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_at_clear = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 0 and d and d.hl_group == 'DiffsClear' and mark[3] == 0 then
+          has_at_clear = true
+        end
+      end
+      assert.is_true(has_at_clear, 'DiffsClear on @@@ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies header diff grammar at syntax priority for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local high_prio_diff = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] < 4 and d and d.hl_group and d.hl_group:match('^@.*%.diff$') and (d.priority or 0) >= 199 then
+          high_prio_diff[mark[2]] = true
+        end
+      end
+      assert.is_true(high_prio_diff[2] ~= nil, 'diff grammar at p>=199 on --- line')
+      assert.is_true(high_prio_diff[3] ~= nil, 'diff grammar at p>=199 on +++ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('@diff.minus wins over @punctuation.special on combined diff headers', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local minus_prio, punct_prio_minus = 0, 0
+      local plus_prio, punct_prio_plus = 0, 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group then
+          if mark[2] == 2 then
+            if d.hl_group == '@diff.minus.diff' then
+              minus_prio = math.max(minus_prio, d.priority or 0)
+            elseif d.hl_group == '@punctuation.special.diff' then
+              punct_prio_minus = math.max(punct_prio_minus, d.priority or 0)
+            end
+          elseif mark[2] == 3 then
+            if d.hl_group == '@diff.plus.diff' then
+              plus_prio = math.max(plus_prio, d.priority or 0)
+            elseif d.hl_group == '@punctuation.special.diff' then
+              punct_prio_plus = math.max(punct_prio_plus, d.priority or 0)
+            end
+          end
+        end
+      end
+      assert.is_true(minus_prio > punct_prio_minus, '@diff.minus.diff should beat @punctuation.special.diff on --- line')
+      assert.is_true(plus_prio > punct_prio_plus, '@diff.plus.diff should beat @punctuation.special.diff on +++ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @keyword.diff on index word for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_keyword = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 1 and d and d.hl_group == '@keyword.diff' and mark[3] == 0 and (d.end_col or 0) == 5 then
+          has_keyword = true
+        end
+      end
+      assert.is_true(has_keyword, '@keyword.diff at row 1, cols 0-5')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @constant.diff on result hash for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_constant = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 1 and d and d.hl_group == '@constant.diff' and (d.priority or 0) >= 199 then
+          has_constant = true
+        end
+      end
+      assert.is_true(has_constant, '@constant.diff on result hash')
+      delete_buffer(bufnr)
+    end)
   end)
 
   describe('extmark priority', function()

From 91a856443f6f4901efb53b6918bda04031106382 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Thu, 5 Mar 2026 01:10:25 -0500
Subject: [PATCH 7/8] ci: format

---
 lua/diffs/highlight.lua | 12 +++++++++++-
 spec/highlight_spec.lua | 26 ++++++++++++++++++++++----
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/lua/diffs/highlight.lua b/lua/diffs/highlight.lua
index 2a2f8b1..a63cf4e 100644
--- a/lua/diffs/highlight.lua
+++ b/lua/diffs/highlight.lua
@@ -370,7 +370,17 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       header_map[i] = hunk.header_start_line - 1 + i
     end
     extmark_count = extmark_count
-      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, qw, nil, p, qw > 0 or pw > 1)
+      + highlight_treesitter(
+        bufnr,
+        ns,
+        hunk.header_lines,
+        'diff',
+        header_map,
+        qw,
+        nil,
+        p,
+        qw > 0 or pw > 1
+      )
   end
 
   local at_raw_line
diff --git a/spec/highlight_spec.lua b/spec/highlight_spec.lua
index 4695d66..58028c9 100644
--- a/spec/highlight_spec.lua
+++ b/spec/highlight_spec.lua
@@ -1669,7 +1669,13 @@ describe('highlight', function()
       local high_prio_diff = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if mark[2] < 4 and d and d.hl_group and d.hl_group:match('^@.*%.diff$') and (d.priority or 0) >= 199 then
+        if
+          mark[2] < 4
+          and d
+          and d.hl_group
+          and d.hl_group:match('^@.*%.diff$')
+          and (d.priority or 0) >= 199
+        then
           high_prio_diff[mark[2]] = true
         end
       end
@@ -1727,8 +1733,14 @@ describe('highlight', function()
           end
         end
       end
-      assert.is_true(minus_prio > punct_prio_minus, '@diff.minus.diff should beat @punctuation.special.diff on --- line')
-      assert.is_true(plus_prio > punct_prio_plus, '@diff.plus.diff should beat @punctuation.special.diff on +++ line')
+      assert.is_true(
+        minus_prio > punct_prio_minus,
+        '@diff.minus.diff should beat @punctuation.special.diff on --- line'
+      )
+      assert.is_true(
+        plus_prio > punct_prio_plus,
+        '@diff.plus.diff should beat @punctuation.special.diff on +++ line'
+      )
       delete_buffer(bufnr)
     end)
 
@@ -1764,7 +1776,13 @@ describe('highlight', function()
       local has_keyword = false
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if mark[2] == 1 and d and d.hl_group == '@keyword.diff' and mark[3] == 0 and (d.end_col or 0) == 5 then
+        if
+          mark[2] == 1
+          and d
+          and d.hl_group == '@keyword.diff'
+          and mark[3] == 0
+          and (d.end_col or 0) == 5
+        then
           has_keyword = true
         end
       end

From a26e9a522c3e1e1b02790928fbae849c338fc762 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Thu, 5 Mar 2026 01:27:00 -0500
Subject: [PATCH 8/8] fix(highlight): prevent duplicate extmarks from two-pass
 rendering

Problem: the deferred pass (pass 2) cleared the hunk range and called
`highlight_hunk` with full opts, reapplying line backgrounds, intra-line
diffs, prefix DiffsClear, and per-char prefix highlights that pass 1
already set. This doubled extmark counts on affected lines.

Solution: add `syntax_only` flag to `diffs.HunkOpts`. When set,
`highlight_hunk` skips non-syntax extmarks (line backgrounds, intra-line,
prefix DiffsClear, per-char prefix fg, hide_prefix overlay, conflict
markers). The deferred pass uses `syntax_only = true` and no longer
clears the namespace range, so pass 1's extmarks persist while pass 2
layers treesitter and content DiffsClear on top.
---
 lua/diffs/highlight.lua | 151 +++++++++++++++++++++-------------------
 lua/diffs/init.lua      |  11 +--
 spec/highlight_spec.lua | 117 +++++++++++++++++++++++++++++++
 3 files changed, 200 insertions(+), 79 deletions(-)

diff --git a/lua/diffs/highlight.lua b/lua/diffs/highlight.lua
index a63cf4e..30c3a59 100644
--- a/lua/diffs/highlight.lua
+++ b/lua/diffs/highlight.lua
@@ -65,6 +65,7 @@ end
 ---@field hide_prefix boolean
 ---@field highlights diffs.Highlights
 ---@field defer_vim_syntax? boolean
+---@field syntax_only? boolean
 
 ---@param bufnr integer
 ---@param ns integer
@@ -398,7 +399,13 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
   ---@type diffs.IntraChanges?
   local intra = nil
   local intra_cfg = opts.highlights.intra
-  if intra_cfg and intra_cfg.enabled and pw == 1 and #hunk.lines <= intra_cfg.max_lines then
+  if
+    not opts.syntax_only
+    and intra_cfg
+    and intra_cfg.enabled
+    and pw == 1
+    and #hunk.lines <= intra_cfg.max_lines
+  then
     dbg('computing intra for hunk %s:%d (%d lines)', hunk.filename, hunk.start_line, #hunk.lines)
     intra = diff.compute_intra_hunks(hunk.lines, intra_cfg.algorithm)
     if intra then
@@ -513,37 +520,80 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
         or content:match('^|||||||')
     end
 
-    if opts.hide_prefix then
-      local virt_hl = (opts.highlights.background and line_hl) or nil
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-        virt_text = { { string.rep(' ', pw + qw), virt_hl } },
-        virt_text_pos = 'overlay',
-      })
-    end
+    if not opts.syntax_only then
+      if opts.hide_prefix then
+        local virt_hl = (opts.highlights.background and line_hl) or nil
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          virt_text = { { string.rep(' ', pw + qw), virt_hl } },
+          virt_text_pos = 'overlay',
+        })
+      end
 
-    if qw > 0 then
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-        end_col = pw + qw,
-        hl_group = 'DiffsClear',
-        priority = p.clear,
-      })
-    elseif pw > 1 then
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-        end_col = pw,
-        hl_group = 'DiffsClear',
-        priority = p.clear,
-      })
-    end
+      if qw > 0 then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          end_col = pw + qw,
+          hl_group = 'DiffsClear',
+          priority = p.clear,
+        })
+      elseif pw > 1 then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          end_col = pw,
+          hl_group = 'DiffsClear',
+          priority = p.clear,
+        })
+      end
 
-    if pw > 1 then
-      for ci = 0, pw - 1 do
-        local ch = line:sub(ci + 1, ci + 1)
-        if ch == '+' or ch == '-' then
-          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, ci + qw, {
-            end_col = ci + qw + 1,
-            hl_group = ch == '+' and '@diff.plus' or '@diff.minus',
-            priority = p.syntax,
-          })
+      if pw > 1 then
+        for ci = 0, pw - 1 do
+          local ch = line:sub(ci + 1, ci + 1)
+          if ch == '+' or ch == '-' then
+            pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, ci + qw, {
+              end_col = ci + qw + 1,
+              hl_group = ch == '+' and '@diff.plus' or '@diff.minus',
+              priority = p.syntax,
+            })
+          end
+        end
+      end
+
+      if opts.highlights.background and is_diff_line then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          line_hl_group = line_hl,
+          number_hl_group = opts.highlights.gutter and number_hl or nil,
+          priority = p.line_bg,
+        })
+      end
+
+      if is_marker and line_len > pw then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, pw + qw, {
+          end_col = line_len + qw,
+          hl_group = 'DiffsConflictMarker',
+          priority = p.char_bg,
+        })
+      end
+
+      if char_spans_by_line[i] then
+        local char_hl = has_add and 'DiffsAddText' or 'DiffsDeleteText'
+        for _, span in ipairs(char_spans_by_line[i]) do
+          dbg(
+            'char extmark: line=%d buf_line=%d col=%d..%d hl=%s text="%s"',
+            i,
+            buf_line,
+            span.col_start,
+            span.col_end,
+            char_hl,
+            line:sub(span.col_start + 1, span.col_end)
+          )
+          local ok, err =
+            pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start + qw, {
+              end_col = span.col_end + qw,
+              hl_group = char_hl,
+              priority = p.char_bg,
+            })
+          if not ok then
+            dbg('char extmark FAILED: %s', err)
+          end
+          extmark_count = extmark_count + 1
         end
       end
     end
@@ -555,47 +605,6 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
         priority = p.clear,
       })
     end
-
-    if opts.highlights.background and is_diff_line then
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
-        line_hl_group = line_hl,
-        number_hl_group = opts.highlights.gutter and number_hl or nil,
-        priority = p.line_bg,
-      })
-    end
-
-    if is_marker and line_len > pw then
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, pw + qw, {
-        end_col = line_len + qw,
-        hl_group = 'DiffsConflictMarker',
-        priority = p.char_bg,
-      })
-    end
-
-    if char_spans_by_line[i] then
-      local char_hl = has_add and 'DiffsAddText' or 'DiffsDeleteText'
-      for _, span in ipairs(char_spans_by_line[i]) do
-        dbg(
-          'char extmark: line=%d buf_line=%d col=%d..%d hl=%s text="%s"',
-          i,
-          buf_line,
-          span.col_start,
-          span.col_end,
-          char_hl,
-          line:sub(span.col_start + 1, span.col_end)
-        )
-        local ok, err =
-          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start + qw, {
-            end_col = span.col_end + qw,
-            hl_group = char_hl,
-            priority = p.char_bg,
-          })
-        if not ok then
-          dbg('char extmark FAILED: %s', err)
-        end
-        extmark_count = extmark_count + 1
-      end
-    end
   end
 
   dbg('hunk %s:%d applied %d extmarks', hunk.filename, hunk.start_line, extmark_count)
diff --git a/lua/diffs/init.lua b/lua/diffs/init.lua
index 6af7e1a..242c247 100644
--- a/lua/diffs/init.lua
+++ b/lua/diffs/init.lua
@@ -797,18 +797,13 @@ local function init()
             return
           end
           local t1 = config.debug and vim.uv.hrtime() or nil
-          local full_opts = {
+          local syntax_opts = {
             hide_prefix = config.hide_prefix,
             highlights = config.highlights,
+            syntax_only = true,
           }
           for _, hunk in ipairs(deferred_syntax) do
-            local start_row = hunk.start_line - 1
-            local end_row = hunk.start_line + #hunk.lines
-            if hunk.header_start_line then
-              start_row = hunk.header_start_line - 1
-            end
-            vim.api.nvim_buf_clear_namespace(bufnr, ns, start_row, end_row)
-            highlight.highlight_hunk(bufnr, ns, hunk, full_opts)
+            highlight.highlight_hunk(bufnr, ns, hunk, syntax_opts)
           end
           if t1 then
             dbg('deferred pass: %d hunks in %.2fms', #deferred_syntax, (vim.uv.hrtime() - t1) / 1e6)
diff --git a/spec/highlight_spec.lua b/spec/highlight_spec.lua
index 58028c9..e3ee12d 100644
--- a/spec/highlight_spec.lua
+++ b/spec/highlight_spec.lua
@@ -1251,6 +1251,123 @@ describe('highlight', function()
       end
       delete_buffer(bufnr)
     end)
+
+    it('two-pass rendering produces no duplicate extmarks', function()
+      vim.api.nvim_set_hl(0, 'DiffsAddText', { bg = 0x00FF00 })
+      vim.api.nvim_set_hl(0, 'DiffsDeleteText', { bg = 0xFF0000 })
+      vim.api.nvim_set_hl(0, 'DiffsAddNr', { fg = 0x80c080, bg = 0x2e4a3a })
+      vim.api.nvim_set_hl(0, 'DiffsDeleteNr', { fg = 0xc08080, bg = 0x4a2e3a })
+
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,2 @@',
+        '-local x = 1',
+        '+local x = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local x = 2' },
+      }
+
+      local fast = default_opts({
+        highlights = {
+          treesitter = { enabled = false },
+          background = true,
+          gutter = true,
+          intra = { enabled = true, algorithm = 'default', max_lines = 500 },
+        },
+      })
+
+      local syntax = default_opts({
+        highlights = {
+          treesitter = { enabled = true },
+          background = true,
+          gutter = true,
+          intra = { enabled = true, algorithm = 'default', max_lines = 500 },
+        },
+      })
+      syntax.syntax_only = true
+
+      highlight.highlight_hunk(bufnr, ns, hunk, fast)
+      highlight.highlight_hunk(bufnr, ns, hunk, syntax)
+
+      local extmarks = get_extmarks(bufnr)
+      for row = 1, 2 do
+        local line_hl_count = 0
+        local number_hl_count = 0
+        local intra_count = 0
+        for _, mark in ipairs(extmarks) do
+          if mark[2] == row then
+            local d = mark[4]
+            if d.line_hl_group then
+              line_hl_count = line_hl_count + 1
+            end
+            if d.number_hl_group then
+              number_hl_count = number_hl_count + 1
+            end
+            if d.hl_group == 'DiffsAddText' or d.hl_group == 'DiffsDeleteText' then
+              intra_count = intra_count + 1
+            end
+          end
+        end
+        assert.are.equal(1, line_hl_count, 'row ' .. row .. ' has duplicate line_hl_group')
+        assert.are.equal(1, number_hl_count, 'row ' .. row .. ' has duplicate number_hl_group')
+        assert.is_true(intra_count <= 1, 'row ' .. row .. ' has duplicate intra extmarks')
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('syntax_only pass adds treesitter without duplicating backgrounds', function()
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,3 @@',
+        ' local x = 1',
+        '+local y = 2',
+        ' return x',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+local y = 2', ' return x' },
+      }
+
+      local fast = default_opts({
+        highlights = {
+          treesitter = { enabled = false },
+          background = true,
+        },
+      })
+
+      local syntax = default_opts({
+        highlights = {
+          treesitter = { enabled = true },
+          background = true,
+        },
+      })
+      syntax.syntax_only = true
+
+      highlight.highlight_hunk(bufnr, ns, hunk, fast)
+      highlight.highlight_hunk(bufnr, ns, hunk, syntax)
+
+      local extmarks = get_extmarks(bufnr)
+      local has_ts = false
+      local line_hl_count = 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group and d.hl_group:match('^@.*%.lua$') then
+          has_ts = true
+        end
+        if d and d.line_hl_group then
+          line_hl_count = line_hl_count + 1
+        end
+      end
+      assert.is_true(has_ts)
+      assert.are.equal(1, line_hl_count)
+      delete_buffer(bufnr)
+    end)
   end)
 
   describe('diff header highlighting', function()