Fix moving point (#363)

When replacing text, calculate the cursor offset relative to the start
of the replacement, not the end of the text-to-be-added.

* test/integration/apheleia-it.el (supports-inserting-whitespace): New
test case
* apheleia-rcs.el (apheleia--apply-rcs-patch): Go to start of deletion
text before calculating offsets

1 files changed, 19 insertions, 0 deletions

diff --git a/test/integration/apheleia-it.el b/test/integration/apheleia-it.el
index d4e9238..b48e420 100644
--- a/test/integration/apheleia-it.el
+++ b/test/integration/apheleia-it.el
@@ -244,3 +244,22 @@ exit 1
                    (lambda (&rest props)
                      (funcall callback (plist-get props :error))))))
            (expect "line4\nline1\n|line2\nline3")))
+
+(apheleia-it-deftest supports-inserting-whitespace
+  "Running `apheleia-format-buffer' preserves point when inserting
+whitespace before point"
+  :scripts `(("apheleia-it" .
+              ,(apheleia-it-script
+                :allowed-inputs
+                '(("function main() {\na=\n  return 0\n}" .
+                   "function main() {\n  a=\n  return 0\n}")))))
+  :formatters '((apheleia-it . ("apheleia-it")))
+  :steps '((insert "function main() {\na=|\n  return 0\n}")
+           (with-callback
+            callback
+            (eval (apheleia-format-buffer
+                   'apheleia-it nil
+                   :callback
+                   (lambda (&rest props)
+                     (funcall callback (plist-get props :error))))))
+           (expect "function main() {\n  a=|\n  return 0\n}")))