Eglot: invalidate local semtok cache at server's bidding

When the server sends workspace/semanticTokens/refresh, calling
font-lock-flush isn't enough.  It will trigger a new
eglot--semtok-font-lock call, but we can't assume anything about
the validity of eglot--semtok-cache.

Clangd seems to send workspace/semanticTokens/refresh when
complicated enough changes happen in an LSP document.  If the
buffer-local eglot--semtok-cache isn't flushed we'll likely
request a delta, and clangd may still supply it, but it won't
apply correctly to the outdated local state.

* lisp/progmodes/eglot.el (eglot--semtok-cache)
(eglot--semtok-inflight): Move up here.
(eglot-handle-request): Flush the eglot--semtok-cache.

1 files changed, 9 insertions, 7 deletions

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index f089745e817..d5a4ca096f3 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -4620,12 +4620,20 @@ If NOERROR, return predicate, else erroring function."
            semtok-cache)
         probe))))
 
+(defvar-local eglot--semtok-cache nil
+  "Cache of the last response from the server.")
+
+(defvar-local eglot--semtok-inflight nil
+  "List of (BEG . END) regions of inflight semtok requests.")
+
 (cl-defmethod eglot-handle-request
   (server (_method (eql workspace/semanticTokens/refresh)))
   "Handle a semanticTokens/refresh request from SERVER."
   (dolist (buffer (eglot--managed-buffers server))
     (eglot--when-live-buffer buffer
-      (unless (zerop eglot--versioned-identifier) (font-lock-flush)))))
+      (unless (zerop eglot--versioned-identifier)
+        (setq eglot--semtok-cache nil)
+        (font-lock-flush)))))
 
 (define-minor-mode eglot-semantic-tokens-mode
   "Minor mode for fontifying buffer with LSP server's semantic tokens."
@@ -4639,12 +4647,6 @@ If NOERROR, return predicate, else erroring function."
          (font-lock-remove-keywords nil '((eglot--semtok-font-lock)))
          (font-lock-flush))))
 
-(defvar-local eglot--semtok-cache nil
-  "Cache of the last response from the server.")
-
-(defvar-local eglot--semtok-inflight nil
-  "List of (BEG . END) regions of inflight semtok requests.")
-
 (defsubst eglot--semtok-apply-delta-edits (old-data edits)
   "Apply EDITS obtained from full/delta request to OLD-DATA."
   (cl-loop