Fix undo information recording for multiline snippets

* yasnippet.el (yas--get-indent-undo-pos): Renamed from
yas--return-first-indent-undo.
(yas-expand-snippet): Bind it to line beginning of snippet expansion
position.
* yasnippet-tests.el (undo-indentation, undo-indentation-multiline):
New tests for this and previous fix.

yasnippet-tests.el

@@ -176,6 +176,39 @@
 ;;     (should (string= (yas--buffer-contents)
 ;;                      "brother from another mother!"))))
 
+(ert-deftest undo-indentation ()
+  "Check undoing works when only line of snippet is indented."
+  (let ((yas-also-auto-indent-first-line t))
+    (yas-with-snippet-dirs
+     '((".emacs.d/snippets" ("emacs-lisp-mode" ("s" . "(setq $0)"))))
+     (with-temp-buffer
+       (emacs-lisp-mode)
+       (yas-minor-mode 1)
+       (insert "(let\n(while s")
+       (setq buffer-undo-list ())
+       (ert-simulate-command '(yas-expand))
+       ;; Need undo barrier, I think command loop puts it normally.
+       (push nil buffer-undo-list)
+       (should (string= (buffer-string) "(let\n    (while (setq )"))
+       (ert-simulate-command '(undo))
+       (should (string= (buffer-string) "(let\n(while s"))))))
+
+(ert-deftest undo-indentation-multiline ()
+  "Check undoing works when first line of multi-line snippet is indented."
+  (yas-with-snippet-dirs
+    '((".emacs.d/snippets" ("js-mode" ("if" . "if ($1) {\n\n}\n"))))
+    (with-temp-buffer
+      (js-mode)
+      (yas-minor-mode 1)
+      (insert "if\nabc = 123456789 + abcdef;")
+      (setq buffer-undo-list ())
+      (goto-char (point-min))
+      (search-forward "if")
+      (ert-simulate-command '(yas-expand))
+      (push nil buffer-undo-list)       ; See test above.
+      (ert-simulate-command '(undo))
+      (should (string= (buffer-string) "if\nabc = 123456789 + abcdef;")))))
+
 (ert-deftest dont-clear-on-partial-deletion-issue-515 ()
   "Ensure fields are not cleared when user doesn't really mean to."
   (with-temp-buffer

yasnippet.el

@@ -3717,9 +3717,10 @@ Move the overlays, or create them if they do not exit."
 (defvar yas--first-indent-undo nil
   "Internal variable for indent undo entries.
 Used to pass info from `yas--indent-region' to `yas-expand-snippet'.")
-(defvar yas--return-first-indent-undo nil
+(defvar yas--get-indent-undo-pos nil
-  "Whether to record undo info in `yas--indent-region'.
+  "Record undo info for line beginning at given position.
-See also `yas--first-indent-undo'.")
+We bind this when first creating a snippet.  See also
+`yas--first-indent-undo'.")
 
 (defun yas-expand-snippet (content &optional start end expand-env)
   "Expand snippet CONTENT at current point.
@@ -3774,7 +3775,7 @@ considered when expanding the snippet."
            ;;
            ;;    stacked expansion: also shoosh the overlay modification hooks
            (let ((buffer-undo-list t)
-                 (yas--return-first-indent-undo t))
+                 (yas--get-indent-undo-pos (line-beginning-position)))
              ;; snippet creation might evaluate users elisp, which
              ;; might generate errors, so we have to be ready to catch
              ;; them mostly to make the undo information
@@ -4199,12 +4200,7 @@ The SNIPPET's markers are preserved."
     (save-restriction
       (widen)
       (let* ((snippet-markers (yas--collect-snippet-markers snippet))
-             (to (set-marker (make-marker) to))
+             (to (set-marker (make-marker) to)))
-             (control-ov (yas--snippet-control-overlay snippet))
-             (1st-bol (progn (goto-char (if control-ov (overlay-start control-ov)
-                                          from))
-                             (beginning-of-line)
-                             (point))))
         (goto-char from)
         (cl-loop for bol = (line-beginning-position)
                  for eol = (line-end-position)
@@ -4217,8 +4213,7 @@ The SNIPPET's markers are preserved."
                              remarkers)))
                    (unwind-protect
                        (progn (back-to-indentation)
-                              (if (and yas--return-first-indent-undo
+                              (if (eq yas--get-indent-undo-pos bol)
-                                       (= 1st-bol bol))
                                   (let ((buffer-undo-list nil))
                                     (indent-according-to-mode)
                                     (setq yas--first-indent-undo