refactor: change highlights.context config to table structure

Problem: highlights.context was a plain integer, inconsistent with the
table structure used by treesitter, vim, and intra sub-configs.

Solution: change to { enabled = true, lines = 25 } with full
vim.validate() coverage matching the existing pattern.

README.md

@@ -43,8 +43,9 @@ luarocks install diffs.nvim
 
 - **Incomplete syntax context**: Treesitter parses each diff hunk in isolation.
   To improve accuracy, `diffs.nvim` reads lines from disk before and after each
-  hunk for parsing context (controlled by `highlights.context`, default 25).
-  This resolves most boundary issues. Set `highlights.context = 0` to disable.
+  hunk for parsing context (`highlights.context`, enabled by default with 25
+  lines). This resolves most boundary issues. Set
+  `highlights.context.enabled = false` to disable.
 
 - **Syntax flashing**: `diffs.nvim` hooks into the `FileType fugitive` event
   triggered by `vim-fugitive`, at which point the buffer is preliminarily

doc/diffs.nvim.txt

@@ -56,7 +56,10 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
       highlights = {
         background = true,
         gutter = true,
-        context = 25,
+        context = {
+          enabled = true,
+          lines = 25,
+        },
         treesitter = {
           enabled = true,
           max_lines = 500,
@@ -114,15 +117,9 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Highlight line numbers with matching colors.
                              Only visible if line numbers are enabled.
 
-        {context}            (integer, default: 25)
-                             Number of lines to read from the source file
-                             before and after each hunk for syntax parsing
-                             context. Improves accuracy at hunk boundaries
-                             where incomplete constructs (e.g., a function
-                             definition with no body) would otherwise confuse
-                             the parser. Set to 0 to disable. Lines are read
-                             from disk with early exit — cost scales with the
-                             context value, not file size.
+        {context}            (table, default: see below)
+                             Syntax parsing context options.
+                             See |diffs.ContextConfig| for fields.
 
         {treesitter}         (table, default: see below)
                              Treesitter highlighting options.
@@ -136,6 +133,20 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Character-level (intra-line) diff highlighting.
                              See |diffs.IntraConfig| for fields.
 
+                                                      *diffs.ContextConfig*
+    Context config fields: ~
+        {enabled}            (boolean, default: true)
+                             Read lines from disk before and after each hunk
+                             to provide surrounding syntax context. Improves
+                             accuracy at hunk boundaries where incomplete
+                             constructs (e.g., a function definition with no
+                             body) would otherwise confuse the parser.
+
+        {lines}              (integer, default: 25)
+                             Number of context lines to read in each
+                             direction. Lines are read with early exit —
+                             cost scales with this value, not file size.
+
                                                     *diffs.TreesitterConfig*
     Treesitter config fields: ~
         {enabled}            (boolean, default: true)
@@ -318,13 +329,13 @@ Incomplete Syntax Context ~
                                                       *diffs-syntax-context*
 Treesitter parses each diff hunk in isolation. To provide surrounding code
 context, diffs.nvim reads lines from disk before and after each hunk
-(controlled by `highlights.context`, default 25). This resolves most boundary
+(see |diffs.ContextConfig|, enabled by default). This resolves most boundary
 issues where incomplete constructs (e.g., a function definition at the edge
 of a hunk with no body) would confuse the parser.
 
-Set `highlights.context = 0` to disable context padding and restore the
-previous behavior. In rare cases, context padding may not help if the
-relevant surrounding code is very far from the hunk boundaries.
+Set `highlights.context.enabled = false` to disable context padding. In rare
+cases, context padding may not help if the relevant surrounding code is very
+far from the hunk boundaries.
 
 Syntax Highlighting Flash ~
                                                              *diffs-flash*

lua/diffs/highlight.lua

@@ -289,7 +289,8 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
   ---@type table<integer, true>
   local covered_lines = {}
 
-  local context = opts.highlights.context or 0
+  local ctx_cfg = opts.highlights.context
+  local context = (ctx_cfg and ctx_cfg.enabled) and ctx_cfg.lines or 0
   local leading = {}
   local trailing = {}
   if (use_ts or use_vim) and context > 0 and hunk.file_new_start and hunk.repo_root then

lua/diffs/init.lua

@@ -11,10 +11,14 @@
 ---@field algorithm string
 ---@field max_lines integer
 
+---@class diffs.ContextConfig
+---@field enabled boolean
+---@field lines integer
+
 ---@class diffs.Highlights
 ---@field background boolean
 ---@field gutter boolean
----@field context integer
+---@field context diffs.ContextConfig
 ---@field treesitter diffs.TreesitterConfig
 ---@field vim diffs.VimConfig
 ---@field intra diffs.IntraConfig
@@ -81,7 +85,10 @@ local default_config = {
   highlights = {
     background = true,
     gutter = true,
-    context = 25,
+    context = {
+      enabled = true,
+      lines = 25,
+    },
     treesitter = {
       enabled = true,
       max_lines = 500,
@@ -233,12 +240,19 @@ local function init()
     vim.validate({
       ['highlights.background'] = { opts.highlights.background, 'boolean', true },
       ['highlights.gutter'] = { opts.highlights.gutter, 'boolean', true },
-      ['highlights.context'] = { opts.highlights.context, 'number', true },
+      ['highlights.context'] = { opts.highlights.context, 'table', true },
       ['highlights.treesitter'] = { opts.highlights.treesitter, 'table', true },
       ['highlights.vim'] = { opts.highlights.vim, 'table', true },
       ['highlights.intra'] = { opts.highlights.intra, 'table', true },
     })
 
+    if opts.highlights.context then
+      vim.validate({
+        ['highlights.context.enabled'] = { opts.highlights.context.enabled, 'boolean', true },
+        ['highlights.context.lines'] = { opts.highlights.context.lines, 'number', true },
+      })
+    end
+
     if opts.highlights.treesitter then
       vim.validate({
         ['highlights.treesitter.enabled'] = { opts.highlights.treesitter.enabled, 'boolean', true },
@@ -294,8 +308,13 @@ local function init()
   if opts.debounce_ms and opts.debounce_ms < 0 then
     error('diffs: debounce_ms must be >= 0')
   end
-  if opts.highlights and opts.highlights.context and opts.highlights.context < 0 then
-    error('diffs: highlights.context must be >= 0')
+  if
+    opts.highlights
+    and opts.highlights.context
+    and opts.highlights.context.lines
+    and opts.highlights.context.lines < 0
+  then
+    error('diffs: highlights.context.lines must be >= 0')
   end
   if
     opts.highlights

spec/highlight_spec.lua

@@ -37,7 +37,7 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
-          context = 0,
+          context = { enabled = false, lines = 0 },
           treesitter = {
             enabled = true,
             max_lines = 500,
@@ -1087,7 +1087,12 @@ describe('highlight', function()
         repo_root = repo_root,
       }
 
-      highlight.highlight_hunk(bufnr, ns, hunk, default_opts({ highlights = { context = 25 } }))
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { context = { enabled = true, lines = 25 } } })
+      )
 
       local extmarks = get_extmarks(bufnr)
       for _, mark in ipairs(extmarks) do
@@ -1100,7 +1105,7 @@ describe('highlight', function()
       vim.fn.delete(repo_root, 'rf')
     end)
 
-    it('context = 0 matches behavior without padding', function()
+    it('context disabled matches behavior without padding', function()
       local bufnr = create_buffer({
         '@@ -1,1 +1,2 @@',
         ' local x = 1',
@@ -1117,7 +1122,12 @@ describe('highlight', function()
         repo_root = '/nonexistent',
       }
 
-      highlight.highlight_hunk(bufnr, ns, hunk, default_opts({ highlights = { context = 0 } }))
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { context = { enabled = false, lines = 0 } } })
+      )
 
       local extmarks = get_extmarks(bufnr)
       assert.is_true(#extmarks > 0)
@@ -1142,7 +1152,12 @@ describe('highlight', function()
       }
 
       assert.has_no.errors(function()
-        highlight.highlight_hunk(bufnr, ns, hunk, default_opts({ highlights = { context = 25 } }))
+        highlight.highlight_hunk(
+          bufnr,
+          ns,
+          hunk,
+          default_opts({ highlights = { context = { enabled = true, lines = 25 } } })
+        )
       end)
 
       local extmarks = get_extmarks(bufnr)
@@ -1180,7 +1195,7 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
-          context = 0,
+          context = { enabled = false, lines = 0 },
           treesitter = { enabled = true, max_lines = 500 },
           vim = { enabled = false, max_lines = 200 },
         },
@@ -1337,7 +1352,7 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
-          context = 0,
+          context = { enabled = false, lines = 0 },
           treesitter = { enabled = true, max_lines = 500 },
           vim = { enabled = false, max_lines = 200 },
         },