Fix dabbrev-completion (bug#17899)

* lisp/dabbrev.el (dabbrev--check-all-buffers): Add new variable.
(dabbrev-completion): Lexical scoping means we can't use let to
override global variables, so use setq.
(dabbrev--reset-global-variables): Reset new variable.
(dabbrev--make-friend-buffer-list): Use new variable.
* test/lisp/dabbrev-tests.el (dabbrev-completion-test):
(dabbrev-completion-test-with-argument): New tests.

1 files changed, 30 insertions, 0 deletions

diff --git a/test/lisp/dabbrev-tests.el b/test/lisp/dabbrev-tests.el
index a6ab2e7201f..d26362db3d4 100644
--- a/test/lisp/dabbrev-tests.el
+++ b/test/lisp/dabbrev-tests.el
@@ -40,3 +40,33 @@ first expansion being replaced rather than the destination."
      ;; M-/ SPC M-/ M-/
      (execute-kbd-macro "\257 \257\257"))
    (should (string= (buffer-string) "ab  x\nab y\nab  y"))))
+
+(ert-deftest dabbrev-completion-test ()
+  "Test for bug#17899.
+dabbrev-completion should not look for expansions in other
+buffers unless a prefix argument is used."
+  (with-temp-buffer
+    (insert "axy")
+    (with-temp-buffer
+      (insert "abc\na")
+      (goto-char 6)
+      (save-window-excursion
+        (set-window-buffer nil (current-buffer))
+        ;; C-M-/
+        (execute-kbd-macro [201326639]))
+      (should (string= (buffer-string) "abc\nabc")))))
+
+(ert-deftest dabbrev-completion-test-with-argument ()
+  "Test for bug#17899.
+dabbrev-completion should not complete because it has found
+multiple expansions."
+  (with-temp-buffer
+    (insert "axy")
+    (with-temp-buffer
+      (insert "abc\na")
+      (goto-char 6)
+      (save-window-excursion
+        (set-window-buffer nil (current-buffer))
+        ;; C-u C-u C-M-/
+        (execute-kbd-macro [21 21 201326639]))
+      (should (string= (buffer-string) "abc\na")))))