Fix Eglot's snippet insertion to follow the manual

The manual states that YASnippet must only be installed to be useful.
Before this change, it would only work if the user happened to have
manually activated it before with 'yas-global-mode' or somesuch.

This makes Eglot's Yasnippet-activating behaviour similar to its
Flymake-activating behaviour.

* lisp/progmodes/eglot.el (eglot-client-capabilities): Consult
eglot--stay-out-of.
(eglot--snippet-expansion-fn): Turn on yas-minor-mod eon demand.
(eglot-completion-at-point): Simplify.

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 52bba717a67ca238df4f8d96e641a8c624f96c2f..68d07c7178afe9fd80791a0b60a31fad79c592d3 100644 (file)
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -758,7 +758,9 @@ treated as in `eglot--dbind'."
              :completion      (list :dynamicRegistration :json-false
                                     :completionItem
                                     `(:snippetSupport
-                                      ,(if (eglot--snippet-expansion-fn)
+                                      ,(if (and
+                                            (not (eglot--stay-out-of-p 'yasnippet))
+                                            (eglot--snippet-expansion-fn))
                                            t
                                          :json-false)
                                       :deprecatedSupport t
@@ -1626,9 +1628,11 @@ If optional MARKER, return a marker instead"
 (defun eglot--snippet-expansion-fn ()
   "Compute a function to expand snippets.
 Doubles as an indicator of snippet support."
-  (and (boundp 'yas-minor-mode)
-       (symbol-value 'yas-minor-mode)
-       'yas-expand-snippet))
+  (and (fboundp 'yas-minor-mode)
+       (lambda (&rest args)
+         (with-no-warnings
+           (unless (bound-and-true-p yas-minor-mode) (yas-minor-mode 1))
+           (apply #'yas-expand-snippet args)))))
 
 (defun eglot--format-markup (markup)
   "Format MARKUP according to LSP's spec."
@@ -2887,8 +2891,7 @@ for which LSP on-type-formatting should be requested."
                                 ;; it'll be adjusted.  If no usable
                                 ;; insertText at all, label is best,
                                 ;; too.
-                                (cond ((or (and (eql insertTextFormat 2)
-                                                (eglot--snippet-expansion-fn))
+                                (cond ((or (eql insertTextFormat 2)
                                            textEdit
                                            (null insertText)
                                            (string-empty-p insertText))