Eglot: unbreak activation/management of derived modes (bug#62907)

After recent changes to how LSP "languageId" is computed from major
modes and stored in the eglot-lsp-server object, the activation of the
'eglot--managed-mode' minor mode in modes _derived_ from some
major-mode mentioned in 'eglot-server-programs' was broken.

This commit restores that by introducing a new helper which uses the
same logic to provide the current-buffer's "languageId" to the server
and to discover if the server should manage the mode at all.  This
ensures the two things stay in sync.

Also, this helper uses the function 'provided-mode-derived-p' to fix
this bug#62907.

* lisp/progmodes/eglot.el (eglot--languageId): New helper.
(eglot-current-server, eglot--TextDocumentItem): Use it.

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 7ad33fa37868e9c4397751438803b747742dc2e6..fe0c986d746104ca2635d449c4ac341218a417be 100644 (file)
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -1935,10 +1935,9 @@ Use `eglot-managed-p' to determine if current buffer is managed.")
   "Return logical Eglot server for current buffer, nil if none."
   (setq eglot--cached-server
         (or eglot--cached-server
-            (cl-find major-mode
-                     (gethash (eglot--current-project) eglot--servers-by-project)
-                     :key #'eglot--major-modes
-                     :test #'memq)
+            (cl-find-if #'eglot--languageId
+                        (gethash (eglot--current-project)
+                                 eglot--servers-by-project))
             (and eglot-extend-to-xref
                  buffer-file-name
                  (gethash (expand-file-name buffer-file-name)
@@ -2360,12 +2359,20 @@ THINGS are either registrations or unregisterations (sic)."
   (append (eglot--TextDocumentIdentifier)
           `(:version ,eglot--versioned-identifier)))
 
+(cl-defun eglot--languageId (&optional (server (eglot--current-server-or-lose)))
+  "Compute LSP \\='languageId\\=' string for current buffer.
+Doubles as an predicate telling if SERVER can manage current
+buffer."
+  (cl-loop for (mode . languageid) in
+           (eglot--languages server)
+           when (provided-mode-derived-p major-mode mode)
+           return languageid))
+
 (defun eglot--TextDocumentItem ()
   "Compute TextDocumentItem object for current buffer."
   (append
    (eglot--VersionedTextDocumentIdentifier)
-   (list :languageId
-         (alist-get major-mode (eglot--languages (eglot--current-server-or-lose)))
+   (list :languageId (eglot--languageId)
          :text
          (eglot--widening
           (buffer-substring-no-properties (point-min) (point-max))))))