Fix setting and resetting of scroll-with-delete

The start and end lines of the scroll region must to be in the range
[0,term-height).  There are few placees that incorrectly set the end
line of the scroll region to term-height which is outside the valid
range.  Combined with another off-by-one error in
term-set-scroll-region's clamping logic, this would cause
term-scroll-with-delete to be unnecessarily turned on.

* lisp/term.el (term-scroll-start,term-scroll-end): Use defvar-local
to define the variables and document the valid range of values that
the variables can take.
(term--last-line): New function to calculate the 0-based index of the
last line.
(term--reset-scroll-region): New function to reset the scroll region
to the full height of the terminal.
(term-mode,term-reset-size,term-reset-terminal): Call
term--reset-scroll-region to reset the scroll region.
(term-set-scroll-region): Fix the off-by-one error in the clamping
logic which allowed term-scroll-end to have values outside the valid
range [0,term-height).

1 files changed, 135 insertions, 1 deletions

diff --git a/test/lisp/term-tests.el b/test/lisp/term-tests.el
index 9f5dcd559eb..6923096d224 100644
--- a/test/lisp/term-tests.el
+++ b/test/lisp/term-tests.el
@@ -119,7 +119,141 @@ line3\r
 line4\r
 line5\r
 line6\r
-"))))
+")))
+
+  ;; test reverse scrolling
+  (should (equal "line1
+line7
+line6
+line2
+line5"
+                 (term-test-screen-from-input 40 5
+                                              '("\e[0;0H"
+                                                "\e[J"
+                                                "line1\r
+line2\r
+line3\r
+line4\r
+line5"
+                                                "\e[2;4r"
+                                                "\e[2;0H"
+                                                "\e[2;0H"
+                                                "\eMline6"
+                                                "\e[2;0H"
+                                                "\eMline7"))))
+
+  ;; test scrolling down
+  (should (equal "line1
+line3
+line4
+line7
+line5"
+                 (term-test-screen-from-input 40 5
+                                              '("\e[0;0H"
+                                                "\e[J"
+                                                "line1\r
+line2\r
+line3\r
+line4\r
+line5"
+                                                "\e[2;4r"
+                                                "\e[2;0H"
+                                                "\e[4;5H"
+                                                "\n\rline7"))))
+
+  ;; setting the scroll region end beyond the max height should not
+  ;; turn on term-scroll-with-delete
+  (should (equal "line1
+line2
+line3
+line4
+line5
+line6
+line7"
+                 (term-test-screen-from-input 40 5
+                                                      '("\e[1;10r"
+                                                        "line1\r
+line2\r
+line3\r
+line4\r
+line5\r
+line6\r
+line7"))))
+
+
+  ;; resetting the terminal should set the scroll region end to (1- term-height).
+  (should (equal "
+line1
+line2
+line3
+line4
+"
+                 (term-test-screen-from-input 40 5
+                                                      '("\e[1;10r"
+                                                        "\ec" ;reset
+                                                        "line1\r
+line2\r
+line3\r
+line4\r
+line5"
+                                                        "\e[1;1H"
+                                                        "\e[L"))))
+
+  ;; scroll region should be limited to the (1- term-height).  Note,
+  ;; this fixes an off by one error when comparing the scroll region
+  ;; end with term-height.
+  (should (equal "
+line1
+line2
+line3
+line4
+"
+                 (term-test-screen-from-input 40 5
+                                              '("\e[1;6r"
+                                                "line1\r
+line2\r
+line3\r
+line4\r
+line5"
+                                                "\e[1;1H" ;go back to home
+                                                "\e[L"    ;insert a new line at the top
+                                                ))))
+
+  ;; setting the scroll region to the entire height should not turn on
+  ;; term-scroll-with-delete
+  (should (equal "line1
+line2
+line3
+line4
+line5
+line6"
+                 (term-test-screen-from-input 40 5
+                                                      '("\e[1;5r"
+                                                        "line1\r
+line2\r
+line3\r
+line4\r
+line5\r
+line6"))))
+
+  ;; reset should reset term-scroll-with-delete
+  (should (equal "line1
+line2
+line3
+line4
+line5
+line6
+line7"
+                 (term-test-screen-from-input 40 5
+                                              '("\e[2;5r" ;set the region
+                                                "\ec" ;reset
+                                                "line1\r
+line2\r
+line3\r
+line4\r
+line5\r
+line6\r
+line7")))))
 
 (ert-deftest term-set-directory ()
   (let ((term-ansi-at-user (user-real-login-name)))