Unbreak Eglot (as a :core ELPA package) on Emacs 26.3

Because of the lack of regular automated testing on a CI system, many
recent developments in and outside Eglot had wrecked this
compatibility.

The GitHub CI available at https://github.com/joaotavora/eglot/actions
can be used to run this combination of eglot.el + eglot-tests.el on
26.3, 27.2 and 28.2.

* etc/EGLOT-NEWS: Mention new version.

* lisp/progmodes/eglot.el (eglot--reporter-update): New
compatibility shim.
(eglot-handle-notification $/progress): Use it.
(eglot-handle-notification textDocument/publishDiagnostics): Use
two-arg assoc-delete-all.
(Version): Bump to 1.13.

* test/lisp/progmodes/eglot-tests.el
(Commentary): Tweak.
(tramp): Tweak require;
(eglot-test-diagnostic-tags-unnecessary-code): Use
jsonrpc--encode.
(eglot--call-with-tramp-test): Adjust dependency on
ert-remote-temporary-file-directory.
(eglot-test-rust-on-type-formatting)
(eglot-test-project-wide-diagnostics-rust-analyzer): Wait longer.

3 files changed, 46 insertions, 30 deletions

diff --git a/etc/EGLOT-NEWS b/etc/EGLOT-NEWS
index dc77e4fe624..dd04e677285 100644
--- a/etc/EGLOT-NEWS
+++ b/etc/EGLOT-NEWS
@@ -12,12 +12,17 @@ This file is about changes in Eglot, the Emacs client for LSP
 (Language Server Protocol) distributed with GNU Emacs since Emacs
 version 29.1 and with GNU ELPA since 2018.
 
-Note: references to Eglot issues are presented as "github#nnnn".
-This refers to https://github.com/joaotavora/eglot/issues/.
-That is, to look up issue github#1234, go to
+Note: references to some Eglot issues are presented as "github#nnnn".
+This refers to https://github.com/joaotavora/eglot/issues/.  That is,
+to look up issue github#1234, go to
 https://github.com/joaotavora/eglot/issues/1234.
 
 
+* Changes in Eglot 1.13 (15/03/2023)
+
+** ELPA installations on Emacs 26.3 are supported again.
+
+
 * Changes in Eglot 1.12 (13/03/2023)
 
 ** LSP inlay hints are now supported.
@@ -328,7 +333,7 @@ This disconnects the server after last managed buffer is killed.
 
 (github#217, github#270)
 
-** Completion support support has been fixed.
+** Completion support has been fixed.
 Among other things, consider LSP's "filterText" cookies, which enable
 a kind of poor-man's flex-matching for some backends.
 
diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 037cc87148f..6c1b9eafe43 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -2,7 +2,7 @@
 
 ;; Copyright (C) 2018-2023 Free Software Foundation, Inc.
 
-;; Version: 1.12
+;; Version: 1.13
 ;; Author: João Távora <joaotavora@gmail.com>
 ;; Maintainer: João Távora <joaotavora@gmail.com>
 ;; URL: https://github.com/joaotavora/eglot
@@ -2147,6 +2147,10 @@ COMMAND is a symbol naming the command."
   (_server (_method (eql telemetry/event)) &rest _any)
   "Handle notification telemetry/event.") ;; noop, use events buffer
 
+(defalias 'eglot--reporter-update
+  (if (> emacs-major-version 26) #'progress-reporter-update
+    (lambda (a b &optional _c) (progress-reporter-update a b))))
+
 (cl-defmethod eglot-handle-notification
   (server (_method (eql $/progress)) &key token value)
   "Handle $/progress notification identified by TOKEN from SERVER."
@@ -2162,10 +2166,10 @@ COMMAND is a symbol naming the command."
                            (make-progress-reporter prefix 0 100 percentage 1 0)
                          (make-progress-reporter prefix nil nil nil 1 0))
                        (eglot--progress-reporters server))))
-             (progress-reporter-update pr percentage (fmt title message))))
+             (eglot--reporter-update pr percentage (fmt title message))))
           ("report"
            (when-let ((pr (gethash token (eglot--progress-reporters server))))
-             (progress-reporter-update pr percentage (fmt title message))))
+             (eglot--reporter-update pr percentage (fmt title message))))
           ("end" (remhash token (eglot--progress-reporters server))))))))
 
 (cl-defmethod eglot-handle-notification
@@ -2183,7 +2187,7 @@ COMMAND is a symbol naming the command."
               (buffer (find-buffer-visiting path)))
         (with-current-buffer buffer
           (cl-loop
-           initially (assoc-delete-all path flymake-list-only-diagnostics #'string=)
+           initially (assoc-delete-all path flymake-list-only-diagnostics)
            for diag-spec across diagnostics
            collect (eglot--dbind ((Diagnostic) range code message severity source tags)
                        diag-spec
@@ -2237,7 +2241,7 @@ COMMAND is a symbol naming the command."
        into diags
        finally
        (setq flymake-list-only-diagnostics
-             (assoc-delete-all path flymake-list-only-diagnostics #'string=))
+             (assoc-delete-all path flymake-list-only-diagnostics))
        (push (cons path diags) flymake-list-only-diagnostics)))))
 
 (cl-defun eglot--register-unregister (server things how)
diff --git a/test/lisp/progmodes/eglot-tests.el b/test/lisp/progmodes/eglot-tests.el
index b95e527c510..7ac26732737 100644
--- a/test/lisp/progmodes/eglot-tests.el
+++ b/test/lisp/progmodes/eglot-tests.el
@@ -31,23 +31,20 @@
 ;; Some of these tests rely on the GNU ELPA package company.el and
 ;; yasnippet.el being available.
 
-;; Some of the tests require access to a remote host files.  Since
-;; this could be problematic, a mock-up connection method "mock" is
-;; used.  Emulating a remote connection, it simply calls "sh -i".
-;; Tramp's file name handlers still run, so this test is sufficient
-;; except for connection establishing.
-
-;; If you want to test a real Tramp connection, set
-;; $REMOTE_TEMPORARY_FILE_DIRECTORY to a suitable value in order to
-;; overwrite the default value.  If you want to skip tests accessing a
-;; remote host, set this environment variable to "/dev/null" or
-;; whatever is appropriate on your system.
+;; Some of the tests require access to a remote host files, which is
+;; mocked in the simplest case.  If you want to test a real Tramp
+;; connection, override $REMOTE_TEMPORARY_FILE_DIRECTORY to a suitable
+;; value (FIXME: like what?) in order to overwrite the default value.
+;;
+;; IMPORTANT: Since Eglot is a :core ELPA package, these tests are
+ ;;supposed to run on Emacsen down to 26.3.  Do not use bleeding-edge
+ ;;functionality not compatible with that Emacs version.
 
 ;;; Code:
 (require 'eglot)
 (require 'cl-lib)
 (require 'ert)
-(require 'tramp) ; must be prior ert-x
+(require 'tramp)
 (require 'ert-x) ; ert-simulate-command
 (require 'edebug)
 (require 'python) ; some tests use pylsp
@@ -463,7 +460,7 @@ then restored."
       (eglot--make-file-or-dir '(".git"))
       (eglot--make-file-or-dir
        `("compile_commands.json" .
-         ,(json-serialize
+         ,(jsonrpc--json-encode
            `[(:directory ,default-directory :command "/usr/bin/c++ -Wall -c main.cpp"
                          :file ,(expand-file-name "main.cpp"))])))
       (let ((eglot-server-programs '((c++-mode . ("clangd")))))
@@ -744,7 +741,7 @@ pylsp prefers autopep over yafp, despite its README stating the contrary."
         (should (zerop (shell-command "cargo init")))
         (eglot--sniffing (:server-notifications s-notifs)
           (should (eglot--tests-connect))
-          (eglot--wait-for (s-notifs 10) (&key method &allow-other-keys)
+          (eglot--wait-for (s-notifs 20) (&key method &allow-other-keys)
              (string= method "textDocument/publishDiagnostics")))
         (goto-char (point-max))
         (eglot--simulate-key-event ?.)
@@ -810,7 +807,7 @@ pylsp prefers autopep over yafp, despite its README stating the contrary."
             (should (= 4 (length (flymake--project-diagnostics))))))))))
 
 (ert-deftest eglot-test-project-wide-diagnostics-rust-analyzer ()
-  "Test diagnostics through multiple files in a TypeScript LSP."
+  "Test diagnostics through multiple files in rust-analyzer."
   (skip-unless (executable-find "rust-analyzer"))
   (skip-unless (executable-find "cargo"))
   (skip-unless (executable-find "git"))
@@ -829,7 +826,7 @@ pylsp prefers autopep over yafp, despite its README stating the contrary."
         (eglot--sniffing (:server-notifications s-notifs)
           (eglot--tests-connect)
           (flymake-start)
-          (eglot--wait-for (s-notifs 15)
+          (eglot--wait-for (s-notifs 20)
               (&key _id method params &allow-other-keys)
             (and (string= method "textDocument/publishDiagnostics")
                  (string-suffix-p "main.rs" (plist-get params :uri))))
@@ -1272,18 +1269,28 @@ macro will assume it exists."
 
 (defvar tramp-histfile-override)
 (defun eglot--call-with-tramp-test (fn)
+  (unless (>= emacs-major-version 27)
+    (ert-skip "Eglot Tramp support only on Emacs >= 27"))
   ;; Set up a Tramp method that’s just a shell so the remote host is
   ;; really just the local host.
-  (let* ((tramp-remote-path (cons 'tramp-own-remote-path tramp-remote-path))
+  (let* ((tramp-remote-path (cons 'tramp-own-remote-path
+                                  tramp-remote-path))
          (tramp-histfile-override t)
          (tramp-verbose 1)
          (temporary-file-directory
           (or (bound-and-true-p ert-remote-temporary-file-directory)
-              temporary-file-directory))
+              (prog1 (format "/mock::%s" temporary-file-directory)
+                (add-to-list
+                 'tramp-methods
+                 '("mock"
+                   (tramp-login-program "sh")       (tramp-login-args (("-i")))
+                   (tramp-direct-async ("-c"))      (tramp-remote-shell "/bin/sh")
+                   (tramp-remote-shell-args ("-c")) (tramp-connection-timeout 10)))
+                (add-to-list 'tramp-default-host-alist
+                             `("\\`mock\\'" nil ,(system-name)))
+                (when (and noninteractive (not (file-directory-p "~/")))
+                  (setenv "HOME" temporary-file-directory)))))
          (default-directory temporary-file-directory))
-    ;; We must check the remote LSP server.  So far, just "clangd" is used.
-    (unless (executable-find "clangd" 'remote)
-      (ert-skip "Remote clangd not found"))
     (funcall fn)))
 
 (ert-deftest eglot-test-tramp-test ()