feat(lsp): pass target buffer to reuse_client predicate #41163

Problem: The reuse_client predicate does not pass the target buffer,
preventing decisions from being truly made per buffer.

Solution: Pass the target buffer.

runtime/doc/lsp.txt

@@ -932,7 +932,7 @@ Lua module: vim.lsp                                                 *lsp-core*
                                filetypes = { 'my_filetype1', 'my_filetype2' },
                              })
 <
-      • {reuse_client}?  (`fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig): boolean`)
+      • {reuse_client}?  (`fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig, bufnr: integer): boolean`)
                          Predicate which decides if a client should be
                          re-used. Used on all running clients. The default
                          implementation re-uses a client if name and root_dir
@@ -1407,7 +1407,7 @@ start({config}, {opts})                                      *vim.lsp.start()*
                   • {bufnr}? (`integer`) Buffer handle to attach to if
                     starting or re-using a client (0 for current).
                   • {reuse_client}?
-                    (`fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig): boolean`)
+                    (`fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig, bufnr: integer): boolean`)
                     Predicate used to decide if a client should be re-used.
                     Used on all running clients. The default implementation
                     re-uses a client if it has the same name and if the given

runtime/doc/news.txt

@@ -330,6 +330,8 @@ LSP
   while a completion item is selected accepts the item as with
   |complete_CTRL-Y|, then inserts the character. Previously
   `commitCharacters` had no effect.
+• The `reuse_client` predicate now passes the target buffer. See |vim.lsp.Config| and
+  |vim.lsp.start()|
 
 LUA
 

runtime/lua/vim/lsp.lua

@@ -191,7 +191,7 @@ end
 ---
 --- Predicate which decides if a client should be re-used. Used on all running clients. The default
 --- implementation re-uses a client if name and root_dir matches.
---- @field reuse_client? fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig): boolean #
+--- @field reuse_client? fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig, bufnr: integer): boolean #
 ---
 --- [lsp-root_dir()]()
 --- Decides the workspace root: the directory where the LSP server will base its workspaceFolders,
@@ -680,7 +680,7 @@ end
 --- running clients. The default implementation re-uses a client if it has the
 --- same name and if the given workspace folders (or root_dir) are all included
 --- in the client's workspace folders.
---- @field reuse_client? fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig): boolean
+--- @field reuse_client? fun(client: vim.lsp.Client, config: vim.lsp.ClientConfig, bufnr: integer): boolean
 ---
 --- Buffer handle to attach to if starting or re-using a client (0 for current).
 --- @field bufnr? integer
@@ -759,7 +759,7 @@ function lsp.start(config, opts)
   end
 
   for _, client in pairs(lsp.client._all) do
-    if reuse_client(client, config) then
+    if reuse_client(client, config, bufnr) then
       if opts.attach == false then
         return client.id
       end