MH-E threads code: use mh-scan variables correctly

* lisp/mh-e/mh-thread.el (mh-thread-current-indentation-level)
(mh-thread-find-children): Fix off-by-one error by using
'mh-scan-field-from-start-offset' directly, as
'mh-thread-parse-scan-line' does.  Previously, these functions would
incorrectly consider the "date note" column as part of the thread
indenting.  Since that column is almost always a Space character, that
almost always worked.
(mh-thread-ancestor): Update caller.
* test/lisp/mh-e/mh-thread-tests.el: New unit tests for affected code.
* lisp/mh-e/mh-scan.el (mh-msg-num-width-to-column): Fix doc string typo.

3 files changed, 137 insertions, 6 deletions

diff --git a/lisp/mh-e/mh-scan.el b/lisp/mh-e/mh-scan.el
index 5a1a671aee2..bf3cfeff5cb 100644
--- a/lisp/mh-e/mh-scan.el
+++ b/lisp/mh-e/mh-scan.el
@@ -509,7 +509,7 @@ with `mh-scan-msg-format-string'."
 Note that columns in Emacs start with 0.
 
 If `mh-scan-format-file' is set to \"Use MH-E scan Format\" this
-means that either `mh-scan-format-mh' or `mh-scan-format-nmh' are
+means that either `mh-scan-format-mh' or `mh-scan-format-nmh' is
 in use.  This function therefore assumes that the first column is
 empty (to provide room for the cursor), the following WIDTH
 columns contain the message number, and the column for notations
diff --git a/lisp/mh-e/mh-thread.el b/lisp/mh-e/mh-thread.el
index 21954da6acd..1be2185ecdf 100644
--- a/lisp/mh-e/mh-thread.el
+++ b/lisp/mh-e/mh-thread.el
@@ -139,7 +139,7 @@ to the message that started everything."
     (cond (thread-root-flag
            (while (mh-thread-immediate-ancestor))
            (mh-maybe-show))
-          ((equal current-level 1)
+          ((equal current-level 0)
            (message "Message has no ancestor"))
           (t (mh-thread-immediate-ancestor)
              (mh-maybe-show)))))
@@ -242,8 +242,8 @@ sibling."
 (defun mh-thread-current-indentation-level ()
   "Find the number of spaces by which current message is indented."
   (save-excursion
-    (let ((address-start-offset (+ mh-cmd-note mh-scan-date-flag-width
-                                   mh-scan-date-width 1))
+    (let ((address-start-offset (+ mh-cmd-note
+                                   mh-scan-field-from-start-offset))
           (level 0))
       (beginning-of-line)
       (forward-char address-start-offset)
@@ -275,8 +275,8 @@ at the end."
   (beginning-of-line)
   (if (eobp)
       nil
-    (let ((address-start-offset (+ mh-cmd-note mh-scan-date-flag-width
-                                   mh-scan-date-width 1))
+    (let ((address-start-offset (+ mh-cmd-note
+                                   mh-scan-field-from-start-offset))
           (level (mh-thread-current-indentation-level))
           spaces begin)
       (setq begin (point))
diff --git a/test/lisp/mh-e/mh-thread-tests.el b/test/lisp/mh-e/mh-thread-tests.el
new file mode 100644
index 00000000000..4f09677e53f
--- /dev/null
+++ b/test/lisp/mh-e/mh-thread-tests.el
@@ -0,0 +1,131 @@
+;;; mh-thread-tests.el --- tests for mh-thread.el -*- lexical-binding: t -*-
+
+;; Copyright (C) 2021 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/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'mh-thread)
+(eval-when-compile (require 'cl-lib))
+
+(defun mh-thread-tests-before-from ()
+  "Generate the fields of a scan line up to where the 'From' field would start.
+The exact contents are not important, but the number of characters is."
+    (concat (make-string mh-cmd-note ?9)
+            (make-string mh-scan-cmd-note-width ?A)
+            (make-string mh-scan-destination-width ?t)
+            (make-string mh-scan-date-width ?/)
+            (make-string mh-scan-date-flag-width ?*)))
+
+;;; Tests of support routines
+
+(ert-deftest mh-thread-current-indentation-level ()
+  "Test that `mh-thread-current-indentation-level' identifies the level."
+  (with-temp-buffer
+    (insert (mh-thread-tests-before-from) "[Sender One]  Subject of msg 1\n")
+    (insert (mh-thread-tests-before-from) "  [Sender Two]  Subject of msg 2\n")
+    (goto-char (point-min))
+    (should (equal 0 (mh-thread-current-indentation-level)))
+    (forward-line)
+    (should (equal 2 (mh-thread-current-indentation-level)))))
+
+(ert-deftest mh-thread-find-children ()
+  "Test `mh-thread-find-children'."
+  (let (expected-start expected-end)
+    (with-temp-buffer
+      (insert (mh-thread-tests-before-from) "[Sender One]  line 1\n")
+      (setq expected-start (point))
+      (insert (mh-thread-tests-before-from) "  [Sender Two]  line 2\n")
+      (insert (mh-thread-tests-before-from) "    [Sender Three]  line 3\n")
+      (insert (mh-thread-tests-before-from) "      [Sender Four]  line 4\n")
+      (setq expected-end (1- (point)))
+      (insert (mh-thread-tests-before-from) "  [Sender Five]  line 5\n")
+      (goto-char (1+ expected-start))
+      (should (equal (list expected-start expected-end)
+                     (mh-thread-find-children))))))
+
+(ert-deftest mh-thread-immediate-ancestor ()
+  "Test that `mh-thread-immediate-ancestor' moves to the correct message."
+  (with-temp-buffer
+    (insert (mh-thread-tests-before-from) "[Sender Other]  line 1\n")
+    (insert (mh-thread-tests-before-from) "[Sender One]  line 2\n")
+    (insert (mh-thread-tests-before-from) "  [Sender Two]  line 3\n")
+    (insert (mh-thread-tests-before-from) "    [Sender Three]  line 4\n")
+    (insert (mh-thread-tests-before-from) "      [Sender Four]  line 5\n")
+    (insert (mh-thread-tests-before-from) "      [Sender Five]  line 6\n")
+    (forward-line -1)
+    (should (equal (line-number-at-pos) 6))
+    (mh-thread-immediate-ancestor)
+    (should (equal (line-number-at-pos) 4)) ;skips over sibling
+    (mh-thread-immediate-ancestor)
+    (should (equal (line-number-at-pos) 3)) ;goes up only one level at a time
+    (mh-thread-immediate-ancestor)
+    (should (equal (line-number-at-pos) 2))
+    (mh-thread-immediate-ancestor)
+    (should (equal (line-number-at-pos) 2)))) ;no further motion at thread root
+
+;;; Tests of MH-Folder Commands
+
+(ert-deftest mh-thread-sibling-and-ancestor ()
+  "Test motion by `mh-thread-ancestor' and `mh-thread-next-sibling'."
+  (with-temp-buffer
+    (insert (mh-thread-tests-before-from) "[Sender Other]  line 1\n")
+    (insert (mh-thread-tests-before-from) "[Sender One]  line 2\n")
+    (insert (mh-thread-tests-before-from) "  [Sender Two]  line 3\n")
+    (insert (mh-thread-tests-before-from) "    [Sender Three]  line 4\n")
+    (insert (mh-thread-tests-before-from) "      [Sender Four]  line 5\n")
+    (insert (mh-thread-tests-before-from) "      [Sender Five]  line 6\n")
+    (forward-line -1)
+    (let ((mh-view-ops '(unthread))
+          (show-count 0))
+      (cl-letf (((symbol-function 'mh-maybe-show)
+                 (lambda ()
+                  (setq show-count (1+ show-count)))))
+        (should (equal (line-number-at-pos) 6))
+        ;; test mh-thread-ancestor
+        (mh-thread-ancestor)
+        (should (equal (line-number-at-pos) 4)) ;skips over sibling
+        (should (equal show-count 1))
+        (mh-thread-ancestor t)
+        (should (equal (line-number-at-pos) 2)) ;root flag skips to root
+        (should (equal show-count 2))
+        (mh-thread-ancestor)
+        (should (equal (line-number-at-pos) 2)) ;do not move from root
+        (should (equal show-count 2))   ;do not re-show at root
+        ;; test mh-thread-sibling
+        (mh-thread-next-sibling)
+        (should (equal (line-number-at-pos) 2)) ;no next sibling, no motion
+        (should (equal show-count 2))   ;no sibling, no show
+        (mh-thread-next-sibling t)
+        (should (equal (line-number-at-pos) 1))
+        (should (equal show-count 3))
+        (mh-thread-next-sibling t)
+        (should (equal (line-number-at-pos) 1)) ;no previous sibling
+        (should (equal show-count 3))
+        (goto-char (point-max))
+        (forward-line -1)
+        (should (equal (line-number-at-pos) 6))
+        (mh-thread-next-sibling t)
+        (should (equal (line-number-at-pos) 5))
+        (should (equal show-count 4))
+        (mh-thread-next-sibling t)
+        (should (equal (line-number-at-pos) 5)) ;no previous sibling
+        (should (equal show-count 4))
+        ))))
+
+;;; mh-thread-tests.el ends here