Fix some compilation warnings

* yasnippet-debug.el (yas--condition-cache-timestamp): Move it before first use.
(yas-debug-live-marker, yas-debug-live-range, yas-debug-snippet-vars)
(yas-debug-process-command-line): Remove or mark unused
variable/parameters.
(yas--letenv): Use `cl-progv'.
(yas--mirror-update-display): Remove unused SNIPPET parameter, update
caller.

yasnippet-debug.el

@@ -91,8 +91,7 @@
           (puthash location (cons color ov) yas-debug-live-indicators)))))
 
 (defun yas-debug-live-marker (marker)
-  (let* ((buffer (current-buffer))
-         (color-ov (yas-debug-get-live-indicator marker))
+  (let* ((color-ov (yas-debug-get-live-indicator marker))
          (color (car color-ov))
          (ov (cdr color-ov))
          (decorator (overlay-get ov 'before-string))
@@ -100,7 +99,7 @@
     (if (markerp marker)
         (propertize str
                     'cursor-sensor-functions
-                    `(,(lambda (window _oldpos dir)
+                    `(,(lambda (_window _oldpos dir)
                          (overlay-put
                           ov 'before-string
                           (propertize decorator
@@ -129,7 +128,7 @@
     (if (and beg end (not (integerp beg)) (not (integerp end)))
         (propertize (format "from %d to %d" (+ beg) (+ end))
                     'cursor-sensor-functions
-                    `(,(lambda (window _oldpos dir)
+                    `(,(lambda (_window _oldpos dir)
                          (let ((face (if (eq dir 'entered)
                                          'mode-line-highlight color)))
                            (overlay-put ov 'before-string
@@ -271,7 +270,7 @@
     (printf "%s overlays in buffer:\n\n" (length (overlays-in (point-min) (point-max))))
     (printf "%s live snippets at point:\n\n" (length (yas-active-snippets)))
 
-    (yas-debug-snippets outbuf)
+    (yas-debug-snippets outbuf) ;;FIXME: reference to free variable ‘outbuf’
 
     (printf "\nUndo is %s and point-max is %s.\n"
             (if (eq buffer-undo-list t)
@@ -286,7 +285,7 @@
         (dolist (undo-elem first-ten)
           (printf "%2s:  %s\n" (cl-position undo-elem first-ten)
                   (truncate-string-to-width (format "%s" undo-elem) 70)))))
-    (display-buffer tracebuf)))
+    (display-buffer tracebuf))) ;;FIXME: reference to free variable ‘tracebuf’
 
 (defun yas--debug-format-fom-concise (fom)
   (when fom
@@ -308,8 +307,7 @@
   (setq yas-verbosity 99)
   (setq yas-triggers-in-field t)
   (setq debug-on-error t)
-  (let* ((snippet-file nil)
-         (snippet-mode 'fundamental-mode)
+  (let* ((snippet-mode 'fundamental-mode)
          (snippet-key nil))
     (unless options
       (setq options (cl-loop for opt = (pop command-line-args-left)

yasnippet.el

@@ -585,6 +585,8 @@ override bindings from other packages (e.g., `company-mode')."
 (defvar yas--minor-mode-menu nil
   "Holds the YASnippet menu.")
 
+(defvar yas--condition-cache-timestamp nil)
+
 (defun yas--maybe-expand-key-filter (cmd)
   (when (let ((yas--condition-cache-timestamp (current-time)))
           (yas--templates-for-key-at-point))
@@ -2183,7 +2185,6 @@ Just put this function in `hippie-expand-try-functions-list'."
 ;;;
 ;;;
 ;;;
-(defvar yas--condition-cache-timestamp nil)
 (defmacro yas-define-condition-cache (func doc &rest body)
   "Define a function FUNC with doc DOC and body BODY.
 BODY is executed at most once every snippet expansion attempt, to check
@@ -3030,7 +3031,9 @@ DEPTH is a count of how many nested mirrors can affect this mirror"
   "Evaluate BODY with bindings from ENV.
 ENV is a list of elements with the form (VAR FORM)."
   (declare (debug (form body)) (indent 1))
-  `(eval (cl-list* 'let* ,env ',body)))
+  (let ((envvar (make-symbol "env")))
+    `(let ((,envvar ,env))
+       (cl-progv (mapcar #'car ,envvar) (mapcar #'cadr ,envvar) . ,body))))
 
 (defun yas--snippet-map-markers (fun snippet)
   "Apply FUN to all marker (sub)fields in SNIPPET.
@@ -4543,7 +4546,7 @@ When multiple expressions are found, only the last one counts."
             (when parent-field
               (yas--advance-start-maybe mirror (yas--fom-start parent-field))))
        ;; Update this mirror.
-       do (yas--mirror-update-display mirror field snippet)
+       do (yas--mirror-update-display mirror field)
        ;; Delay indenting until we're done all mirrors.  We must do
        ;; this to avoid losing whitespace between fields that are
        ;; still empty (i.e., they will be non-empty after updating).
@@ -4560,7 +4563,7 @@ When multiple expressions are found, only the last one counts."
          (cl-loop for (beg . end) in (cl-sort indent-regions #'< :key #'car)
                   do (yas--indent-region beg end snippet)))))))
 
-(defun yas--mirror-update-display (mirror field snippet)
+(defun yas--mirror-update-display (mirror field)
   "Update MIRROR according to FIELD (and mirror transform)."
 
   (let* ((mirror-parent-field (yas--mirror-parent-field mirror))