feat(snippet): highlight active tabstop (#35378)

runtime/colors/vim.lua

@@ -134,6 +134,7 @@ hi('DiagnosticDeprecated',       { sp = 'Red', strikethrough = true,    cterm =
 hi('DiagnosticUnnecessary', { link = 'Comment' })
 hi('LspInlayHint',          { link = 'NonText' })
 hi('SnippetTabstop',        { link = 'Visual' })
+hi('SnippetTabstopActive',  { link = 'SnippetTabstop' })
 
 -- Text
 hi('@markup.raw',       { link = 'Comment' })

runtime/doc/lua.txt

@@ -4354,7 +4354,8 @@ vim.snippet.expand({input})                             *vim.snippet.expand()*
     https://microsoft.github.io/language-server-protocol/specification/#snippet_syntax
     for the specification of valid input.
 
-    Tabstops are highlighted with |hl-SnippetTabstop|.
+    Tabstops are highlighted with |hl-SnippetTabstop| and
+    |hl-SnippetTabstopActive|.
 
     Parameters: ~
       • {input}  (`string`)

runtime/doc/news.txt

@@ -192,6 +192,7 @@ HIGHLIGHTS
 
 • |hl-DiffTextAdd| highlights added text within a changed line.
 • |hl-StderrMsg| |hl-StdoutMsg|
+• |hl-SnippetTabstopActive| highlights the currently active tabstop.
 
 LSP
 

runtime/doc/syntax.txt

@@ -5343,6 +5343,9 @@ Search		Last search pattern highlighting (see 'hlsearch').
 		Also used for similar items that need to stand out.
 							*hl-SnippetTabstop*
 SnippetTabstop	Tabstops in snippets. |vim.snippet|
+							*hl-SnippetTabstopActive*
+SnippetTabstopActive
+		The currently active tabstop. |vim.snippet|
 							*hl-SpecialKey*
 SpecialKey	Unprintable characters: Text displayed differently from what
 		it really is. But not 'listchars' whitespace. |hl-Whitespace|

runtime/lua/vim/snippet.lua

@@ -2,6 +2,7 @@ local G = vim.lsp._snippet_grammar
 local snippet_group = vim.api.nvim_create_augroup('nvim.snippet', {})
 local snippet_ns = vim.api.nvim_create_namespace('nvim.snippet')
 local hl_group = 'SnippetTabstop'
+local hl_group_active = 'SnippetTabstopActive'
 
 --- Returns the 0-based cursor position.
 ---
@@ -124,7 +125,7 @@ function Tabstop.new(index, bufnr, placement, range, choices)
     end_right_gravity = false,
     end_line = range[3],
     end_col = range[4],
-    hl_group = hl_group,
+    hl_group = index == 1 and hl_group_active or hl_group,
   })
 
   local self = setmetatable({
@@ -168,19 +169,22 @@ function Tabstop:set_text(text)
 end
 
 ---@alias (private) vim.snippet.TabStopGravity
---- | "expand" Expand the (usually current) tabstop on text insert
+--- | "expand" Expand the current tabstop on text insert
 --- | "lock" The tabstop should NOT move on text insert
 --- | "shift" The tabstop should move on text insert (default)
 
 --- Sets the right gravity of the tabstop's extmark.
+--- Sets the active highlight group for current ("expand") tabstops
 ---
 ---@package
 ---@param target vim.snippet.TabStopGravity
 function Tabstop:set_gravity(target)
+  local hl = hl_group
   local right_gravity = true
   local end_right_gravity = true
 
   if target == 'expand' then
+    hl = hl_group_active
     right_gravity = false
     end_right_gravity = true
   elseif target == 'lock' then
@@ -189,12 +193,13 @@ function Tabstop:set_gravity(target)
   end
 
   local range = self:get_range()
+  vim.api.nvim_buf_del_extmark(self.bufnr, snippet_ns, self.extmark_id)
   self.extmark_id = vim.api.nvim_buf_set_extmark(self.bufnr, snippet_ns, range[1], range[2], {
     right_gravity = right_gravity,
     end_right_gravity = end_right_gravity,
     end_line = range[3],
     end_col = range[4],
-    hl_group = hl_group,
+    hl_group = hl,
   })
 end
 
@@ -469,7 +474,7 @@ end
 --- Refer to https://microsoft.github.io/language-server-protocol/specification/#snippet_syntax
 --- for the specification of valid input.
 ---
---- Tabstops are highlighted with |hl-SnippetTabstop|.
+--- Tabstops are highlighted with |hl-SnippetTabstop| and |hl-SnippetTabstopActive|.
 ---
 --- @param input string
 function M.expand(input)

src/nvim/highlight_group.c

@@ -221,6 +221,7 @@ static const char *highlight_init_both[] = {
   "default link LspReferenceTarget          LspReferenceText",
   "default link LspSignatureActiveParameter Visual",
   "default link SnippetTabstop              Visual",
+  "default link SnippetTabstopActive        SnippetTabstop",
 
   // Diagnostic
   "default link DiagnosticFloatingError    DiagnosticError",

test/functional/lua/snippet_spec.lua

@@ -116,6 +116,20 @@ describe('vim.snippet', function()
     test_expand_success({ 'print($UNKNOWN)' }, { 'print(UNKNOWN)' })
   end)
 
+  it('highlights active tabstop with SnippetTabstopActive', function()
+    local function get_extmark_details(col, end_col)
+      return api.nvim_buf_get_extmarks(0, -1, { 0, col }, { 0, end_col }, { details = true })[1][4]
+    end
+
+    test_expand_success({ 'local ${1:name} = ${2:value}' }, { 'local name = value' })
+    eq('SnippetTabstopActive', get_extmark_details(6, 10).hl_group)
+    eq('SnippetTabstop', get_extmark_details(13, 18).hl_group)
+    feed('<Tab>')
+    poke_eventloop()
+    eq('SnippetTabstop', get_extmark_details(6, 10).hl_group)
+    eq('SnippetTabstopActive', get_extmark_details(13, 18).hl_group)
+  end)
+
   it('does not jump outside snippet range', function()
     test_expand_success({ 'function $1($2)', '  $0', 'end' }, { 'function ()', '  ', 'end' })
     eq(false, exec_lua('return vim.snippet.active({ direction = -1 })'))