feat(config): replace algorithm 'auto'/'native' with 'default'/'vscode'

'default' inherits algorithm and linematch from diffopt, 'vscode' uses
the FFI library. Removes the need for diffs.nvim to duplicate settings
that users already control globally.

README.md

@@ -17,6 +17,7 @@ syntax highlighting.
 - Background-only diff colors for any `&diff` buffer (`:diffthis`, `vimdiff`)
 - Vim syntax fallback for languages without a treesitter parser
 - Hunk header context highlighting (`@@ ... @@ function foo()`)
+- Character-level (intra-line) diff highlighting for changed characters
 - Configurable debouncing, max lines, and diff prefix concealment
 
 ## Requirements

doc/diffs.nvim.txt

@@ -66,7 +66,7 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
         },
         intra = {
           enabled = true,
-          algorithm = 'auto',
+          algorithm = 'default',
           max_lines = 500,
         },
       },
@@ -158,12 +158,12 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              an intense background overlay while the rest of the
                              line keeps the softer line-level background.
 
-        {algorithm}          (string, default: 'auto')
+        {algorithm}          (string, default: 'default')
                              Diff algorithm for character-level analysis.
-                             `'auto'`: use libvscodediff if available, else
+                             `'default'`: use |vim.diff()| with settings
-                             native `vim.diff()`. `'native'`: always use
+                             inherited from |'diffopt'| (`algorithm` and
-                             `vim.diff()`. `'vscode'`: require libvscodediff
+                             `linematch`). `'vscode'`: use libvscodediff FFI
-                             (falls back to native if not available).
+                             (falls back to default if not available).
 
         {max_lines}          (integer, default: 500)
                              Skip character-level highlighting for hunks larger
@@ -285,8 +285,8 @@ Summary / commit detail views: ~
    - Code is parsed with |vim.treesitter.get_string_parser()|
    - If no treesitter parser and `vim.enabled`: vim syntax fallback via
      scratch buffer and |synID()|
-   - Background extmarks (`DiffsAdd`/`DiffsDelete`) at priority 198
+   - `Normal` extmarks at priority 198 clear underlying diff foreground
-   - `Normal` extmarks at priority 199 clear underlying diff foreground
+   - Background extmarks (`DiffsAdd`/`DiffsDelete`) at priority 199
    - Syntax highlights are applied as extmarks at priority 200
    - Character-level diff extmarks (`DiffsAddText`/`DiffsDeleteText`) at
      priority 201 overlay changed characters with an intense background
@@ -383,15 +383,14 @@ Fugitive unified diff highlights: ~
                                                               *DiffsAddText*
     DiffsAddText        Character-level background for changed characters
                         within `+` lines. Derived by blending `diffAdded`
-                        foreground with `Normal` background at 40% alpha.
+                        foreground with `Normal` background at 70% alpha.
-                        Uses the same base color as `DiffsAddNr` foreground,
+                        Only sets `bg`, so treesitter foreground colors show
-                        making changed characters clearly visible. Only sets
+                        through.
-                        `bg`, so treesitter foreground colors show through.
 
                                                            *DiffsDeleteText*
     DiffsDeleteText     Character-level background for changed characters
                         within `-` lines. Derived by blending `diffRemoved`
-                        foreground with `Normal` background at 40% alpha.
+                        foreground with `Normal` background at 70% alpha.
 
 Diff mode window highlights: ~
 These are used for |winhighlight| remapping in `&diff` windows.

lua/diffs/diff.lua

@@ -60,11 +60,35 @@ function M.extract_change_groups(hunk_lines)
   return groups
 end
 
+---@return {algorithm?: string, linematch?: integer}
+local function parse_diffopt()
+  local opts = {}
+  for _, item in ipairs(vim.split(vim.o.diffopt, ',')) do
+    local key, val = item:match('^(%w+):(.+)$')
+    if key == 'algorithm' then
+      opts.algorithm = val
+    elseif key == 'linematch' then
+      opts.linematch = tonumber(val)
+    end
+  end
+  return opts
+end
+
 ---@param old_text string
 ---@param new_text string
+---@param diff_opts? {algorithm?: string, linematch?: integer}
 ---@return {old_start: integer, old_count: integer, new_start: integer, new_count: integer}[]
-local function byte_diff(old_text, new_text)
+local function byte_diff(old_text, new_text, diff_opts)
-  local ok, result = pcall(vim.diff, old_text, new_text, { result_type = 'indices' })
+  local vim_opts = { result_type = 'indices' }
+  if diff_opts then
+    if diff_opts.algorithm then
+      vim_opts.algorithm = diff_opts.algorithm
+    end
+    if diff_opts.linematch then
+      vim_opts.linematch = diff_opts.linematch
+    end
+  end
+  local ok, result = pcall(vim.diff, old_text, new_text, vim_opts)
   if not ok or not result then
     return {}
   end
@@ -95,8 +119,9 @@ end
 ---@param new_line string
 ---@param del_idx integer
 ---@param add_idx integer
+---@param diff_opts? {algorithm?: string, linematch?: integer}
 ---@return diffs.CharSpan[], diffs.CharSpan[]
-local function char_diff_pair(old_line, new_line, del_idx, add_idx)
+local function char_diff_pair(old_line, new_line, del_idx, add_idx, diff_opts)
   ---@type diffs.CharSpan[]
   local del_spans = {}
   ---@type diffs.CharSpan[]
@@ -108,7 +133,7 @@ local function char_diff_pair(old_line, new_line, del_idx, add_idx)
   local old_text = table.concat(old_bytes, '\n') .. '\n'
   local new_text = table.concat(new_bytes, '\n') .. '\n'
 
-  local char_hunks = byte_diff(old_text, new_text)
+  local char_hunks = byte_diff(old_text, new_text, diff_opts)
 
   for _, ch in ipairs(char_hunks) do
     if ch.old_count > 0 then
@@ -132,8 +157,9 @@ local function char_diff_pair(old_line, new_line, del_idx, add_idx)
 end
 
 ---@param group diffs.ChangeGroup
+---@param diff_opts? {algorithm?: string, linematch?: integer}
 ---@return diffs.CharSpan[], diffs.CharSpan[]
-local function diff_group_native(group)
+local function diff_group_native(group, diff_opts)
   ---@type diffs.CharSpan[]
   local all_del = {}
   ---@type diffs.CharSpan[]
@@ -147,7 +173,8 @@ local function diff_group_native(group)
       group.del_lines[1].text,
       group.add_lines[1].text,
       group.del_lines[1].idx,
-      group.add_lines[1].idx
+      group.add_lines[1].idx,
+      diff_opts
     )
     vim.list_extend(all_del, ds)
     vim.list_extend(all_add, as)
@@ -166,7 +193,7 @@ local function diff_group_native(group)
   local old_block = table.concat(old_texts, '\n') .. '\n'
   local new_block = table.concat(new_texts, '\n') .. '\n'
 
-  local line_hunks = byte_diff(old_block, new_block)
+  local line_hunks = byte_diff(old_block, new_block, diff_opts)
 
   ---@type table<integer, integer>
   local old_to_new = {}
@@ -184,7 +211,8 @@ local function diff_group_native(group)
         group.del_lines[old_i].text,
         group.add_lines[new_i].text,
         group.del_lines[old_i].idx,
-        group.add_lines[new_i].idx
+        group.add_lines[new_i].idx,
+        diff_opts
       )
       vim.list_extend(all_del, ds)
       vim.list_extend(all_add, as)
@@ -202,7 +230,8 @@ local function diff_group_native(group)
             group.del_lines[oi].text,
             group.add_lines[ni].text,
             group.del_lines[oi].idx,
-            group.add_lines[ni].idx
+            group.add_lines[ni].idx,
+            diff_opts
           )
           vim.list_extend(all_del, ds)
           vim.list_extend(all_add, as)
@@ -295,16 +324,25 @@ function M.compute_intra_hunks(hunk_lines, algorithm)
     return nil
   end
 
-  algorithm = algorithm or 'auto'
+  algorithm = algorithm or 'default'
 
-  local lib = require('diffs.lib')
   local vscode_handle = nil
-  if algorithm ~= 'native' then
+  if algorithm == 'vscode' then
-    vscode_handle = lib.load()
+    vscode_handle = require('diffs.lib').load()
+    if not vscode_handle then
+      dbg('vscode algorithm requested but library not available, falling back to default')
+    end
   end
 
-  if algorithm == 'vscode' and not vscode_handle then
+  local diff_opts = nil
-    dbg('vscode algorithm requested but library not available, falling back to native')
+  if not vscode_handle then
+    diff_opts = parse_diffopt()
+    if diff_opts.algorithm then
+      dbg('diffopt algorithm: %s', diff_opts.algorithm)
+    end
+    if diff_opts.linematch then
+      dbg('diffopt linematch: %d', diff_opts.linematch)
+    end
   end
 
   ---@type diffs.CharSpan[]
@@ -325,7 +363,7 @@ function M.compute_intra_hunks(hunk_lines, algorithm)
     if vscode_handle then
       ds, as = diff_group_vscode(group, vscode_handle)
     else
-      ds, as = diff_group_native(group)
+      ds, as = diff_group_native(group, diff_opts)
     end
     dbg('group %d result: %d del spans, %d add spans', gi, #ds, #as)
     for _, s in ipairs(ds) do

lua/diffs/init.lua

@@ -90,7 +90,7 @@ local default_config = {
     },
     intra = {
       enabled = true,
-      algorithm = 'auto',
+      algorithm = 'default',
       max_lines = 500,
     },
   },
@@ -259,9 +259,9 @@ local function init()
         ['highlights.intra.algorithm'] = {
           opts.highlights.intra.algorithm,
           function(v)
-            return v == nil or v == 'auto' or v == 'native' or v == 'vscode'
+            return v == nil or v == 'default' or v == 'vscode'
           end,
-          "'auto', 'native', or 'vscode'",
+          "'default' or 'vscode'",
         },
         ['highlights.intra.max_lines'] = { opts.highlights.intra.max_lines, 'number', true },
       })

spec/diff_spec.lua

@@ -73,17 +73,17 @@ describe('diff', function()
 
   describe('compute_intra_hunks', function()
     it('returns nil for all-addition hunks', function()
-      local result = diff.compute_intra_hunks({ '+line1', '+line2' }, 'native')
+      local result = diff.compute_intra_hunks({ '+line1', '+line2' }, 'default')
       assert.is_nil(result)
     end)
 
     it('returns nil for all-deletion hunks', function()
-      local result = diff.compute_intra_hunks({ '-line1', '-line2' }, 'native')
+      local result = diff.compute_intra_hunks({ '-line1', '-line2' }, 'default')
       assert.is_nil(result)
     end)
 
     it('returns nil for context-only hunks', function()
-      local result = diff.compute_intra_hunks({ ' line1', ' line2' }, 'native')
+      local result = diff.compute_intra_hunks({ ' line1', ' line2' }, 'default')
       assert.is_nil(result)
     end)
 
@@ -91,7 +91,7 @@ describe('diff', function()
       local result = diff.compute_intra_hunks({
         '-local x = 1',
         '+local x = 2',
-      }, 'native')
+      }, 'default')
       assert.is_not_nil(result)
       assert.is_true(#result.del_spans > 0)
       assert.is_true(#result.add_spans > 0)
@@ -101,7 +101,7 @@ describe('diff', function()
       local result = diff.compute_intra_hunks({
         '-local x = 1',
         '+local x = 2',
-      }, 'native')
+      }, 'default')
       assert.is_not_nil(result)
 
       assert.are.equal(1, #result.del_spans)
@@ -121,7 +121,7 @@ describe('diff', function()
         ' local b = 3',
         '-local c = 4',
         '+local c = 5',
-      }, 'native')
+      }, 'default')
       assert.is_not_nil(result)
       assert.is_true(#result.del_spans >= 2)
       assert.is_true(#result.add_spans >= 2)
@@ -132,7 +132,7 @@ describe('diff', function()
         '-line one',
         '-line two',
         '+line combined',
-      }, 'native')
+      }, 'default')
       assert.is_not_nil(result)
     end)
 
@@ -140,7 +140,7 @@ describe('diff', function()
       local result = diff.compute_intra_hunks({
         '-local x = "héllo"',
         '+local x = "wörld"',
-      }, 'native')
+      }, 'default')
       assert.is_not_nil(result)
       assert.is_true(#result.del_spans > 0)
       assert.is_true(#result.add_spans > 0)
@@ -150,7 +150,7 @@ describe('diff', function()
       local result = diff.compute_intra_hunks({
         '-local x = 1',
         '+local x = 1',
-      }, 'native')
+      }, 'default')
       assert.is_nil(result)
     end)
   end)

spec/highlight_spec.lua

@@ -45,7 +45,7 @@ describe('highlight', function()
           },
           intra = {
             enabled = false,
-            algorithm = 'native',
+            algorithm = 'default',
             max_lines = 500,
           },
         },
@@ -828,7 +828,7 @@ describe('highlight', function()
         default_opts({
           highlights = {
             background = true,
-            intra = { enabled = true, algorithm = 'native', max_lines = 500 },
+            intra = { enabled = true, algorithm = 'default', max_lines = 500 },
           },
         })
       )
@@ -873,7 +873,7 @@ describe('highlight', function()
         ns,
         hunk,
         default_opts({
-          highlights = { intra = { enabled = true, algorithm = 'native', max_lines = 500 } },
+          highlights = { intra = { enabled = true, algorithm = 'default', max_lines = 500 } },
         })
       )
 
@@ -913,7 +913,7 @@ describe('highlight', function()
         ns,
         hunk,
         default_opts({
-          highlights = { intra = { enabled = false, algorithm = 'native', max_lines = 500 } },
+          highlights = { intra = { enabled = false, algorithm = 'default', max_lines = 500 } },
         })
       )
 
@@ -947,7 +947,7 @@ describe('highlight', function()
         ns,
         hunk,
         default_opts({
-          highlights = { intra = { enabled = true, algorithm = 'native', max_lines = 500 } },
+          highlights = { intra = { enabled = true, algorithm = 'default', max_lines = 500 } },
         })
       )
 
@@ -984,7 +984,7 @@ describe('highlight', function()
         default_opts({
           highlights = {
             background = true,
-            intra = { enabled = true, algorithm = 'native', max_lines = 500 },
+            intra = { enabled = true, algorithm = 'default', max_lines = 500 },
           },
         })
       )