feat(lsp): lsp.completion support set deprecated (#29882)

Problem: CompletionItem in lsp spec mentioned the deprecated attribute

Solution: when item has deprecated attribute set hl_group to DiagnosticDeprecated
          in complete function

runtime/lua/vim/lsp/completion.lua

@@ -253,6 +253,13 @@ function M._lsp_to_complete_items(result, prefix, client_id)
   for _, item in ipairs(items) do
     if matches(item) then
       local word = get_completion_word(item)
+      local hl_group = ''
+      if
+        item.deprecated
+        or vim.list_contains((item.tags or {}), protocol.CompletionTag.Deprecated)
+      then
+        hl_group = 'DiagnosticDeprecated'
+      end
       table.insert(candidates, {
         word = word,
         abbr = item.label,
@@ -262,6 +269,7 @@ function M._lsp_to_complete_items(result, prefix, client_id)
         icase = 1,
         dup = 1,
         empty = 1,
+        hl_group = hl_group,
         user_data = {
           nvim = {
             lsp = {

runtime/lua/vim/lsp/protocol.lua

@@ -99,6 +99,13 @@ local constants = {
     TriggerForIncompleteCompletions = 3,
   },
 
+  -- Completion item tags are extra annotations that tweak the rendering of a
+  -- completion item
+  CompletionTag = {
+    -- Render a completion as obsolete, usually using a strike-out.
+    Deprecated = 1,
+  },
+
   -- A document highlight kind.
   DocumentHighlightKind = {
     -- A textual occurrence.
@@ -433,13 +440,16 @@ function protocol.make_client_capabilities()
           snippetSupport = true,
           commitCharactersSupport = false,
           preselectSupport = false,
-          deprecatedSupport = false,
+          deprecatedSupport = true,
           documentationFormat = { constants.MarkupKind.Markdown, constants.MarkupKind.PlainText },
           resolveSupport = {
             properties = {
               'additionalTextEdits',
             },
           },
+          tagSupport = {
+            valueSet = get_value_set(constants.CompletionTag),
+          },
         },
         completionItemKind = {
           valueSet = get_value_set(constants.CompletionItemKind),

test/functional/plugin/lsp/completion_spec.lua

@@ -307,6 +307,7 @@ describe('vim.lsp.completion: item conversion', function()
       info = '',
       kind = 'Module',
       menu = '',
+      hl_group = '',
       word = 'this_thread',
     }
     local result = complete('  std::this|', completion_list)
@@ -362,6 +363,7 @@ describe('vim.lsp.completion: item conversion', function()
       info = '',
       kind = 'Module',
       menu = '',
+      hl_group = '',
       word = 'this_thread',
     }
     local result = complete('  std::this|is', completion_list)
@@ -529,6 +531,14 @@ describe('vim.lsp.completion: protocol', function()
         {
           label = 'hello',
         },
+        {
+          label = 'hercules',
+          tags = { 1 }, -- 1 represents Deprecated tag
+        },
+        {
+          label = 'hero',
+          deprecated = true,
+        },
       },
     })
 
@@ -545,6 +555,7 @@ describe('vim.lsp.completion: protocol', function()
           info = '',
           kind = 'Unknown',
           menu = '',
+          hl_group = '',
           user_data = {
             nvim = {
               lsp = {
@@ -557,6 +568,50 @@ describe('vim.lsp.completion: protocol', function()
           },
           word = 'hello',
         },
+        {
+          abbr = 'hercules',
+          dup = 1,
+          empty = 1,
+          icase = 1,
+          info = '',
+          kind = 'Unknown',
+          menu = '',
+          hl_group = 'DiagnosticDeprecated',
+          user_data = {
+            nvim = {
+              lsp = {
+                client_id = 1,
+                completion_item = {
+                  label = 'hercules',
+                  tags = { 1 },
+                },
+              },
+            },
+          },
+          word = 'hercules',
+        },
+        {
+          abbr = 'hero',
+          dup = 1,
+          empty = 1,
+          icase = 1,
+          info = '',
+          kind = 'Unknown',
+          menu = '',
+          hl_group = 'DiagnosticDeprecated',
+          user_data = {
+            nvim = {
+              lsp = {
+                client_id = 1,
+                completion_item = {
+                  label = 'hero',
+                  deprecated = true,
+                },
+              },
+            },
+          },
+          word = 'hero',
+        },
       }, matches)
     end)
   end)