Make clang-include-fixer--insert-line work when the difference is on an empty line

[tmarek]

Summary

clang-include-fixer--insert-line has an off-by-one error because it uses (goto-char (point-min)) (forward-char chars), which is (goto-char (1+ chars)). Because of this, when the first difference was on an empty line (i.e. an include was appended to the block of includes), the pointer in the to` buffer would be on the next line.

Also wrapped calls inside another process sentinel inside with-local-quit.

[klimek]

lg

include-fixer/tool/clang-include-fixer-test.el

(with-temp-buffer
     (let ((from (current-buffer)))
       (with-temp-buffer
         (insert "aa\nac\nad\n")
         (let ((to (current-buffer)))
           (should (clang-include-fixer--insert-line from to))
           (should (equal (buffer-string) "aa\nab\nac\nad\n")))))
     (should (equal (buffer-string) "aa\nab\nac\nad\n"))))
 
+(ert-deftest clang-include-fixer--insert-line-diff-on-empty-line ()
+  "Unit test for `clang-include-fixer--insert-line'."
+  (with-temp-buffer
+    (insert "aa\nab\n\nac\nad\n")
+    (let ((from (current-buffer)))
+      (with-temp-buffer
+        (insert "aa\n\nac\nad\n")
+        (let ((to (current-buffer)))
+          (should (clang-include-fixer--insert-line from to))
+          (should (equal (buffer-string) "aa\nab\n\nac\nad\n")))))
+    (should (equal (buffer-string) "aa\nab\n\nac\nad\n"))))
+
 (ert-deftest clang-include-fixer--symbol-at-point ()
   "Unit test for `clang-include-fixer--symbol-at-point'."
   (with-temp-buffer
     (insert "a+bbb::cc")
     (c++-mode)
     (goto-char (point-min))
     (should (equal (clang-include-fixer--symbol-at-point) "a"))
     (forward-char)

include-fixer/tool/clang-include-fixer.el

(save-excursion
           (save-excursion
             (save-restriction
               (widen)
               ;; Search for the first buffer difference.
               (let ((chars (abs (compare-buffer-substrings to nil nil from nil nil))))
                 (if (zerop chars)
                     ;; Buffer contents are equal, nothing to do.
                     t
-                  (goto-char (point-min))
-                  (forward-char chars)
+                  (goto-char chars)
                   ;; We might have ended up in the middle of a line if the
                   ;; current line partially matches.  In this case we would
                   ;; have to insert more than a line.  Move to the beginning of
                   ;; the line to avoid this situation.
                   (beginning-of-line)
                   (with-current-buffer from
-                    (goto-char (point-min))
-                    (forward-char chars)
+                    (goto-char chars)
                     (beginning-of-line)
                     (let ((from-begin (point))
                           (from-end (progn (forward-line) (point)))
                           (to-point (with-current-buffer to (point))))
                       ;; Search for another buffer difference after the line in
                       ;; question.  If there is none, we can proceed.
                       (when (zerop (compare-buffer-substrings from from-end nil
                                                               to to-point nil))
(let-alist context
              (lambda (stdout)
                (when (/= old-tick (buffer-chars-modified-tick))
                  ;; Replacing the buffer now would undo the user’s changes.
                  (user-error (concat "The buffer has been changed "
                                      "before the header could be inserted")))
                (clang-include-fixer--replace-buffer stdout)
                (let-alist context
                  (let-alist (car .HeaderInfos)
+                   (with-local-quit
                      (run-hook-with-args 'clang-include-fixer-add-include-hook
                                          (substring .Header 1 -1)
-                                       (string= (substring .Header 0 1) "<"))))))
+                                         (string= (substring .Header 0 1) "<")))))))
            (format "-insert-header=%s"
                    (clang-include-fixer--encode-json context))))))))
   nil)
 
 (defun clang-include-fixer--select-header (context)
   "Prompt the user for a header if necessary.
 CONTEXT must be a clang-include-fixer context object in
 association list format.  If it contains more than one HeaderInfo