Preserve point in pascal-mode completion (bug#41740)

Failure to do so caused errors in several cases.
Reported by Shinichi Sakata.

* lisp/progmodes/pascal.el (pascal-type-completion)
(pascal-completion): Wrap code that may move point in save-excursion.
* test/lisp/progmodes/pascal-tests.el: New file.

2 files changed, 82 insertions, 24 deletions

diff --git a/lisp/progmodes/pascal.el b/lisp/progmodes/pascal.el
index 536a16dbb3c..b0191c029b9 100644
--- a/lisp/progmodes/pascal.el
+++ b/lisp/progmodes/pascal.el
@@ -1170,26 +1170,27 @@ indent of the current line in parameterlist."
 
 (defun pascal-type-completion (pascal-str)
   "Calculate all possible completions for types."
-  (let ((start (point))
-        (pascal-all ())
-        goon)
-    ;; Search for all reachable type declarations
-    (while (or (pascal-beg-of-defun)
-               (setq goon (not goon)))
-      (save-excursion
-        (if (and (< start (prog1 (save-excursion (pascal-end-of-defun)
-                                                 (point))
-                            (forward-char 1)))
-                 (re-search-forward
-                  "\\<type\\>\\|\\<\\(begin\\|function\\|procedure\\)\\>"
-                  start t)
-                 (not (match-end 1)))
-            ;; Check current type declaration
-            (setq pascal-all
-                  (nconc (pascal-get-completion-decl pascal-str)
-                         pascal-all)))))
+  (save-excursion
+    (let ((start (point))
+          (pascal-all ())
+          goon)
+      ;; Search for all reachable type declarations
+      (while (or (pascal-beg-of-defun)
+                 (setq goon (not goon)))
+        (save-excursion
+          (if (and (< start (prog1 (save-excursion (pascal-end-of-defun)
+                                                   (point))
+                              (forward-char 1)))
+                   (re-search-forward
+                    "\\<type\\>\\|\\<\\(begin\\|function\\|procedure\\)\\>"
+                    start t)
+                   (not (match-end 1)))
+              ;; Check current type declaration
+              (setq pascal-all
+                    (nconc (pascal-get-completion-decl pascal-str)
+                           pascal-all)))))
 
-    pascal-all))
+      pascal-all)))
 
 (defun pascal-var-completion (prefix)
   "Calculate all possible completions for variables (or constants)."
@@ -1263,11 +1264,13 @@ indent of the current line in parameterlist."
                     (and (eq state 'defun)
                          (save-excursion
                            (re-search-backward ")[ \t]*:" (point-at-bol) t))))
-                (if (or (eq state 'paramlist) (eq state 'defun))
-                    (pascal-beg-of-defun))
-                (nconc
-                 (pascal-type-completion pascal-str)
-                 (pascal-keyword-completion pascal-type-keywords pascal-str)))
+                (save-excursion
+                  (if (or (eq state 'paramlist) (eq state 'defun))
+                      (pascal-beg-of-defun))
+                  (nconc
+                   (pascal-type-completion pascal-str)
+                   (pascal-keyword-completion pascal-type-keywords
+                                              pascal-str))))
                (                        ;--Starting a new statement
                 (and (not (eq state 'contexp))
                      (save-excursion
diff --git a/test/lisp/progmodes/pascal-tests.el b/test/lisp/progmodes/pascal-tests.el
new file mode 100644
index 00000000000..10d6e0433d0
--- /dev/null
+++ b/test/lisp/progmodes/pascal-tests.el
@@ -0,0 +1,55 @@
+;;; pascal-tests.el --- tests for pascal.el    -*- lexical-binding: t -*-
+
+;; Copyright (C) 2020 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+(require 'ert)
+(require 'pascal)
+
+(ert-deftest pascal-completion ()
+  ;; Bug#41740: completion functions must preserve point.
+  (let ((pascal-completion-cache nil))
+    (with-temp-buffer
+      (pascal-mode)
+      (insert "program test; var")
+      (let* ((point-before (point))
+             (completions (pascal-completion "var" nil 'metadata))
+             (point-after (point)))
+        (should (equal completions nil))
+        (should (equal point-before point-after)))))
+
+  (let ((pascal-completion-cache nil))
+    (with-temp-buffer
+      (pascal-mode)
+      (insert "program test; function f(x : i")
+      (let* ((point-before (point))
+             (completions (pascal-completion "i" nil 'metadata))
+             (point-after (point)))
+        (should (equal completions nil))
+        (should (equal point-before point-after)))))
+
+  (let ((pascal-completion-cache nil))
+    (with-temp-buffer
+      (pascal-mode)
+      (insert "program test; function f(x : integer) : real")
+      (let* ((point-before (point))
+             (completions (pascal-completion "real" nil 'metadata))
+             (point-after (point)))
+        (should (equal completions nil))
+        (should (equal point-before point-after))))))
+
+(provide 'pascal-tests)