fix(lsp): better handling of "*" configs

Problem:

If a config name contains "*" it causes rtp discovery of `lsp/` to
consider the `*` as a wildcard and could lead to strange and unintended
behaviour. For example, accessing the `'*'` config from a `lsp/` file
would cause an infinite loop.

Solution:

- Explicitly disallow a config name from containing wildcards, with the
  exception of `'*'`.
- When Resolving `'*'` config, skip the rtp step.

runtime/lua/vim/lsp.lua

@@ -377,6 +377,19 @@ local function invalidate_enabled_config(name)
   end
 end
 
+--- @param name any
+local function validate_config_name(name)
+  validate('name', name, function(value)
+    if type(value) ~= 'string' then
+      return false
+    end
+    if value ~= '*' and value:match('%*') then
+      return false, 'LSP config name cannot contain wildcard ("*")'
+    end
+    return true
+  end, 'non-wildcard string')
+end
+
 --- @nodoc
 --- @class vim.lsp.config
 --- @field [string] vim.lsp.Config
@@ -386,11 +399,16 @@ lsp.config = setmetatable({ _configs = {} }, {
   --- @param name string
   --- @return vim.lsp.Config
   __index = function(self, name)
-    validate('name', name, 'string')
+    validate_config_name(name)
 
     local rconfig = lsp._enabled_configs[name] or {}
 
     if not rconfig.resolved_config then
+      if name == '*' then
+        rconfig.resolved_config = lsp.config._configs['*'] or {}
+        return rconfig.resolved_config
+      end
+
       -- Resolve configs from lsp/*.lua
       -- Calls to vim.lsp.config in lsp/* have a lower precedence than calls from other sites.
       local rtp_config --- @type vim.lsp.Config?
@@ -400,12 +418,12 @@ lsp.config = setmetatable({ _configs = {} }, {
           --- @type vim.lsp.Config?
           rtp_config = vim.tbl_deep_extend('force', rtp_config or {}, config)
         else
-          log.warn(string.format('%s does not return a table, ignoring', v))
+          log.warn(('%s does not return a table, ignoring'):format(v))
         end
       end
 
       if not rtp_config and not self._configs[name] then
-        log.warn(string.format('%s does not have a configuration', name))
+        log.warn(('%s does not have a configuration'):format(name))
         return
       end
 
@@ -425,7 +443,7 @@ lsp.config = setmetatable({ _configs = {} }, {
   --- @param name string
   --- @param cfg vim.lsp.Config
   __newindex = function(self, name, cfg)
-    validate('name', name, 'string')
+    validate_config_name(name)
     validate('cfg', cfg, 'table')
     invalidate_enabled_config(name)
     self._configs[name] = cfg
@@ -435,7 +453,7 @@ lsp.config = setmetatable({ _configs = {} }, {
   --- @param name string
   --- @param cfg vim.lsp.Config
   __call = function(self, name, cfg)
-    validate('name', name, 'string')
+    validate_config_name(name)
     validate('cfg', cfg, 'table')
     invalidate_enabled_config(name)
     self[name] = vim.tbl_deep_extend('force', self._configs[name] or {}, cfg)

test/functional/plugin/lsp_spec.lua

@@ -6449,5 +6449,36 @@ describe('LSP', function()
         end)
       )
     end)
+
+    it('does not allow wildcards in config name', function()
+      local err =
+        '.../lsp.lua:0: name: expected non%-wildcard string, got foo%*%. Info: LSP config name cannot contain wildcard %("%*"%)'
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          local _ = vim.lsp.config['foo*']
+        end)
+      )
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          vim.lsp.config['foo*'] = {}
+        end)
+      )
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          vim.lsp.config('foo*', {})
+        end)
+      )
+
+      -- Exception for '*'
+      pcall(exec_lua, function()
+        vim.lsp.config('*', {})
+      end)
+    end)
   end)
 end)