feat(lsp): add a registry for client side code action commands

This builds on https://github.com/neovim/neovim/pull/14112 and closes
https://github.com/neovim/neovim/issues/12326

runtime/lua/vim/lsp.lua

@@ -1534,5 +1534,34 @@ function lsp._with_extend(name, options, user_config)
   return resulting_config
 end
 
+
+--- Registry for client side commands.
+--- This is an extension point for plugins to handle custom commands which are
+--- not part of the core language server protocol specification.
+---
+--- The registry is a table where the key is a unique command name,
+--- and the value is a function which is called if any LSP action
+--- (code action, code lenses, ...) triggers the command.
+---
+--- If a LSP response contains a command for which no matching entry is
+--- available in this registry, the command will be executed via the LSP server
+--- using `workspace/executeCommand`.
+---
+--- The first argument to the function will be the `Command`:
+--    Command
+--      title: String
+--      command: String
+--      arguments?: any[]
+--
+--- The second argument is the `ctx` of |lsp-handler|
+lsp.commands = setmetatable({}, {
+  __newindex = function(tbl, key, value)
+    assert(type(key) == 'string', "The key for commands in `vim.lsp.commands` must be a string")
+    assert(type(value) == 'function', "Command added to `vim.lsp.commands` must be a function")
+    rawset(tbl, key, value)
+  end;
+})
+
+
 return lsp
 -- vim:sw=2 ts=2 et

runtime/lua/vim/lsp/handlers.lua

@@ -110,7 +110,7 @@ M['client/registerCapability'] = function(_, _, ctx)
 end
 
 --see: https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_codeAction
-M['textDocument/codeAction'] = function(_, result)
+M['textDocument/codeAction'] = function(_, result, ctx)
   if result == nil or vim.tbl_isempty(result) then
     print("No code actions available")
     return
@@ -127,19 +127,28 @@ M['textDocument/codeAction'] = function(_, result)
   if choice < 1 or choice > #result then
     return
   end
-  local action_chosen = result[choice]
-  -- textDocument/codeAction can return either Command[] or CodeAction[].
-  -- If it is a CodeAction, it can have either an edit, a command or both.
-  -- Edits should be executed first
-  if action_chosen.edit or type(action_chosen.command) == "table" then
-    if action_chosen.edit then
-      util.apply_workspace_edit(action_chosen.edit)
-    end
-    if type(action_chosen.command) == "table" then
-      buf.execute_command(action_chosen.command)
-    end
+  local action = result[choice]
+  -- textDocument/codeAction can return either Command[] or CodeAction[]
+  --
+  -- CodeAction
+  --  ...
+  --  edit?: WorkspaceEdit    -- <- must be applied before command
+  --  command?: Command
+  --
+  -- Command:
+  --  title: string
+  --  command: string
+  --  arguments?: any[]
+  --
+  if action.edit then
+    util.apply_workspace_edit(action.edit)
+  end
+  local command = type(action.command) == 'table' and action.command or action
+  local fn = vim.lsp.commands[command.command]
+  if fn then
+    fn(command, ctx)
   else
-    buf.execute_command(action_chosen)
+    buf.execute_command(command)
   end
 end
 

test/functional/plugin/lsp_spec.lua

@@ -2374,4 +2374,42 @@ describe('LSP', function()
     end
   end)
 
+  describe('vim.lsp.buf.code_action', function()
+    it('Calls client side command if available', function()
+      eq(1, exec_lua [[
+        local dummy_calls = 0
+        vim.lsp.commands.dummy = function()
+          dummy_calls = dummy_calls + 1
+        end
+        local actions = {
+          {
+            title = 'Dummy command',
+            command = 'dummy',
+          },
+        }
+        -- inputlist would require input and block the test;
+        vim.fn.inputlist = function()
+          return 1
+        end
+        local params = {}
+        local handler = require'vim.lsp.handlers'['textDocument/codeAction']
+        handler(nil, actions, { method = 'textDocument/codeAction', params = params }, nil)
+        return dummy_calls
+      ]])
+    end)
+  end)
+  describe('vim.lsp.commands', function()
+    it('Accepts only string keys', function()
+      matches(
+        '.*The key for commands in `vim.lsp.commands` must be a string',
+        pcall_err(exec_lua, 'vim.lsp.commands[1] = function() end')
+      )
+    end)
+    it('Accepts only function values', function()
+      matches(
+        '.*Command added to `vim.lsp.commands` must be a function',
+        pcall_err(exec_lua, 'vim.lsp.commands.dummy = 10')
+      )
+    end)
+  end)
 end)