Eglot: Make 'try-completion' less broken

The 'try-completion' completion operation, used mostly in vanilla
'completion-at-point' invoked with C-M-i is close to impossible to get
right in LSP because of the arbitrary edits handled in
':exit-function'.

When this operation is invoked on the table, returning the pattern
argument unchanged somehow (TM) makes a sole completion show the
*Completions* buffer, where selecting it will recover context
necessary for `:exit-function' and call that function.  It doesn't
break any other cases I know, and that's good enough for now.

https://github.com/joaotavora/eglot/issues/1339

* lisp/progmodes/eglot.el (eglot-completion-at-point): Return pattern
when 'try-completion' is invoked.

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index d777e488c4350a99b16ea295b55af840c98fb7b9..a97c9e2a3e086f8ff75ebb0d01940074b8fc3045 100644 (file)
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -3113,8 +3113,8 @@ for which LSP on-type-formatting should be requested."
           ((eq action 'lambda)                           ; test-completion
            (test-completion pattern (funcall proxies)))
           ((eq (car-safe action) 'boundaries) nil)       ; boundaries
-          ((null action)                                 ; try-completion
-           (try-completion pattern (funcall proxies)))
+          ((null action)                                 ; try-completion (github#1339)
+           pattern)
           ((eq action t)                                 ; all-completions
            (let ((comps (funcall proxies)))
              (dolist (c comps) (eglot--dumb-flex pattern c t))
@@ -3215,7 +3215,8 @@ for which LSP on-type-formatting should be requested."
                         ;; was obtained from server. If a `proxy'
                         ;; "bar" was obtained from a buffer with
                         ;; "foo.b", the LSP edit applies to that
-                        ;; state, _not_ the current "foo.bar".
+                        ;; state, _not_ the current "foo.bar"
+                        ;; (github#1339)
                         (delete-region orig-pos (point))
                         (insert (substring bounds-string (- orig-pos (car bounds))))
                         (eglot--dbind ((TextEdit) range newText) textEdit