fix(lsp/diagnostic): key resultId by client and identifier

Previously, resultId for diagnostics was keyed only by client_id, which
could cause issues when multiple identifiers are used by the same client.
This change introduces a composite key of client_id and identifier for
client_result_id, ensuring correct tracking of diagnostic results per
identifier. Updates all relevant logic to use the new keying scheme.

runtime/lua/vim/lsp/diagnostic.lua

@@ -15,7 +15,7 @@ local augroup = api.nvim_create_augroup('nvim.lsp.diagnostic', {})
 
 ---@class (private) vim.lsp.diagnostic.BufState
 ---@field pull_kind 'document'|'workspace'|'disabled' Whether diagnostics are being updated via document pull, workspace pull, or disabled.
----@field client_result_id table<integer, string?> Latest responded `resultId`
+---@field client_result_id table<string, string?> Latest responded `resultId`, keyed by `client_id.identifier`
 
 ---@type table<integer, vim.lsp.diagnostic.BufState>
 local bufstates = {}
@@ -147,6 +147,13 @@ local function tags_vim_to_lsp(diagnostic)
   return tags
 end
 
+---@param client_id integer
+---@param identifier string|nil
+---@return string
+local function result_id_key(client_id, identifier)
+  return string.format('%d.%s', client_id, identifier or 'nil')
+end
+
 --- Converts the input `vim.Diagnostic`s to LSP diagnostics.
 --- @param diagnostics vim.Diagnostic[]
 --- @return lsp.Diagnostic[]
@@ -281,14 +288,15 @@ function M.on_diagnostic(error, result, ctx)
   local client_id = ctx.client_id
   local bufnr = assert(ctx.bufnr)
   local bufstate = bufstates[bufnr]
-  bufstate.client_result_id[client_id] = result.resultId
+  ---@type lsp.DocumentDiagnosticParams
+  local params = ctx.params
+  local key = result_id_key(client_id, params.identifier)
+  bufstate.client_result_id[key] = result.resultId
 
   if result.kind == 'unchanged' then
     return
   end
 
-  ---@type lsp.DocumentDiagnosticParams
-  local params = ctx.params
   handle_diagnostics(params.textDocument.uri, client_id, result.items, params.identifier or true)
 
   for uri, related_result in pairs(result.relatedDocuments or {}) do
@@ -304,7 +312,7 @@ function M.on_diagnostic(error, result, ctx)
       or { pull_kind = 'document', client_result_id = {} }
     bufstates[related_bufnr] = related_bufstate
 
-    related_bufstate.client_result_id[client_id] = related_result.resultId
+    related_bufstate.client_result_id[key] = related_result.resultId
   end
 end
 
@@ -383,11 +391,12 @@ function M._refresh(bufnr, client_id, only_visible)
   for _, client in ipairs(clients) do
     ---@param cap lsp.DiagnosticRegistrationOptions
     client:_provider_foreach(method, function(cap)
+      local key = result_id_key(client.id, cap.identifier)
       ---@type lsp.DocumentDiagnosticParams
       local params = {
         identifier = cap.identifier,
         textDocument = util.make_text_document_params(bufnr),
-        previousResultId = bufstate.client_result_id[client.id],
+        previousResultId = bufstate.client_result_id[key],
       }
       client:request(method, params, nil, bufnr)
     end)
@@ -481,19 +490,20 @@ end
 
 --- Returns the result IDs from the reports provided by the given client.
 --- @return lsp.PreviousResultId[]
-local function previous_result_ids(client_id)
+--- @param client_id integer
+--- @param identifier string|nil
+local function previous_result_ids(client_id, identifier)
   local results = {} ---@type lsp.PreviousResultId[]
+  local key = result_id_key(client_id, identifier)
 
   for bufnr, state in pairs(bufstates) do
     if state.pull_kind ~= 'disabled' then
-      for buf_client_id, result_id in pairs(state.client_result_id) do
-        if buf_client_id == client_id then
-          results[#results + 1] = {
-            uri = vim.uri_from_bufnr(bufnr),
-            value = result_id,
-          }
-          break
-        end
+      local result_id = state.client_result_id[key]
+      if result_id then
+        results[#results + 1] = {
+          uri = vim.uri_from_bufnr(bufnr),
+          value = result_id,
+        }
       end
     end
   end
@@ -535,7 +545,8 @@ function M._workspace_diagnostics(opts)
         -- state if we're not pulling document diagnostics for this buffer.
         if bufstates[bufnr].pull_kind == 'workspace' and report.kind == 'full' then
           handle_diagnostics(report.uri, ctx.client_id, report.items, params.identifier or true)
-          bufstates[bufnr].client_result_id[ctx.client_id] = report.resultId
+          local key = result_id_key(ctx.client_id, params.identifier)
+          bufstates[bufnr].client_result_id[key] = report.resultId
         end
       end
     end
@@ -547,7 +558,7 @@ function M._workspace_diagnostics(opts)
       --- @type lsp.WorkspaceDiagnosticParams
       local params = {
         identifier = cap.identifier,
-        previousResultIds = previous_result_ids(client.id),
+        previousResultIds = previous_result_ids(client.id, cap.identifier),
       }
 
       client:request('workspace/diagnostic', params, handler)