feat(lsp): options to filter and auto-apply code actions (#18221)

Implement two new options to vim.lsp.buf.code_action():
 - filter (function): predicate taking an Action as input, and returning
   a boolean.
 - apply (boolean): when set to true, and there is just one remaining
   action (after filtering), the action is applied without user query.

These options can, for example, be used to filter out, and automatically
apply, the action indicated by the server to be preferred:

    vim.lsp.buf.code_action({
        filter = function(action)
            return action.isPreferred
        end,
        apply = true,
    })

Fix #17514.

2 files changed, 66 insertions, 0 deletions

diff --git a/test/functional/fixtures/fake-lsp-server.lua b/test/functional/fixtures/fake-lsp-server.lua
index 7ff3713d41..3375a5dda9 100644
--- a/test/functional/fixtures/fake-lsp-server.lua
+++ b/test/functional/fixtures/fake-lsp-server.lua
@@ -673,6 +673,36 @@ function tests.code_action_with_resolve()
   }
 end
 
+function tests.code_action_filter()
+  skeleton {
+    on_init = function()
+      return {
+        capabilities = {
+          codeActionProvider = {
+            resolveProvider = false
+          }
+        }
+      }
+    end;
+    body = function()
+      notify('start')
+      local action = {
+        title = 'Action 1',
+        command = 'command'
+      }
+      local preferred_action = {
+        title = 'Action 2',
+        isPreferred = true,
+        command = 'preferred_command',
+      }
+      expect_request('textDocument/codeAction', function()
+        return nil, { action, preferred_action, }
+      end)
+      notify('shutdown')
+    end;
+  }
+end
+
 function tests.clientside_commands()
   skeleton {
     on_init = function()
diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index 436b431e38..03ed167bac 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -2665,6 +2665,42 @@ describe('LSP', function()
         end
       }
     end)
+    it('Filters and automatically applies action if requested', function()
+      local client
+      local expected_handlers = {
+        {NIL, {}, {method="shutdown", client_id=1}};
+        {NIL, {}, {method="start", client_id=1}};
+      }
+      test_rpc_server {
+        test_name = 'code_action_filter',
+        on_init = function(client_)
+          client = client_
+        end,
+        on_setup = function()
+        end,
+        on_exit = function(code, signal)
+          eq(0, code, "exit code", fake_lsp_logfile)
+          eq(0, signal, "exit signal", fake_lsp_logfile)
+        end,
+        on_handler = function(err, result, ctx)
+          eq(table.remove(expected_handlers), {err, result, ctx})
+          if ctx.method == 'start' then
+            exec_lua([[
+              vim.lsp.commands['preferred_command'] = function(cmd)
+                vim.lsp.commands['executed_preferred'] = function()
+                end
+              end
+              local bufnr = vim.api.nvim_get_current_buf()
+              vim.lsp.buf_attach_client(bufnr, TEST_RPC_CLIENT_ID)
+              vim.lsp.buf.code_action({ filter = function(a) return a.isPreferred end, apply = true, })
+            ]])
+          elseif ctx.method == 'shutdown' then
+            eq('function', exec_lua[[return type(vim.lsp.commands['executed_preferred'])]])
+            client.stop()
+          end
+        end
+      }
+    end)
   end)
   describe('vim.lsp.commands', function()
     it('Accepts only string keys', function()