feat(lsp): return table from lsp/ files on runtimepath (#31663)

Problem: LSP configs on the runtimepath must have the same name as the
LSP server and must also explicitly set the name in vim.lsp.config. This
is redundant and creates a footgun where a user may accidentally use the
wrong name when assigning to the vim.lsp.config table.

Solution: Return a table from lsp/ runtimepath files instead

runtime/doc/lsp.txt

@@ -74,12 +74,8 @@ configurations, in increasing priority, from the following:
 
 1. Configuration defined for the `'*'` name.
 
-2. Configuration from the result of sourcing all `lsp/<name>.lua` files
-   in 'runtimepath' for a server of name `name`.
-
-   Note: because of this, calls to |vim.lsp.config()| in `lsp/*.lua` are
-   treated independently to other calls. This ensures configurations
-   defined in `lsp/*.lua` have a lower priority.
+2. Configuration from the result of merging all tables returned by
+   `lsp/<name>.lua` files in 'runtimepath' for a server of name `name`.
 
 3. Configurations defined anywhere else.
 
@@ -102,11 +98,11 @@ Given: >lua
   })
 
   -- Defined in ../lsp/clangd.lua
-  vim.lsp.config('clangd', {
+  return {
     cmd = { 'clangd' },
     root_markers = { '.clangd', 'compile_commands.json' },
     filetypes = { 'c', 'cpp' },
-  })
+  }
 
   -- Defined in init.lua
   vim.lsp.config('clangd', {

runtime/doc/news.txt

@@ -22,6 +22,12 @@ EXPERIMENTS
 
 • Removed `vim.loader.disable()`. Use `vim.loader.enable(false)` instead.
 
+LSP
+
+• `lsp/` runtimepath files should return a table instead of calling
+  |vim.lsp.config()| (or assigning to `vim.lsp.config`). See |lsp-config|
+
+
 OPTIONS
 
 • 'jumpoptions' flag "unload" has been renamed to "clean".

runtime/lua/vim/lsp.lua

@@ -450,16 +450,20 @@ function lsp._resolve_config(name)
   if not econfig.resolved_config then
     -- Resolve configs from lsp/*.lua
     -- Calls to vim.lsp.config in lsp/* have a lower precedence than calls from other sites.
-    local orig_configs = lsp.config._configs
-    lsp.config._configs = {}
-    pcall(vim.cmd.runtime, { ('lsp/%s.lua'):format(name), bang = true })
-    local rtp_configs = lsp.config._configs
-    lsp.config._configs = orig_configs
+    local rtp_config = {} ---@type vim.lsp.Config
+    for _, v in ipairs(api.nvim_get_runtime_file(('lsp/%s.lua'):format(name), true)) do
+      local config = assert(loadfile(v))() ---@type any?
+      if type(config) == 'table' then
+        rtp_config = vim.tbl_deep_extend('force', rtp_config, config)
+      else
+        log.warn(string.format('%s does not return a table, ignoring', v))
+      end
+    end
 
     local config = vim.tbl_deep_extend(
       'force',
       lsp.config._configs['*'] or {},
-      rtp_configs[name] or {},
+      rtp_config,
       lsp.config._configs[name] or {}
     )