Fix bug running Prettier on modified buffer

CHANGELOG.md

@@ -3,6 +3,15 @@
 All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog].
 
+## Unreleased
+### Bugs fixed
+* Previously, weirdness could happen if manually running Prettier via
+  `M-x apheleia-format-buffer` on a buffer which was modified from
+  what was written to disk. Now we simply abort running a command that
+  uses the `file` keyword if the buffer is modified, since it will not
+  produce correct results. This should not affect normal usage of
+  Apheleia.
+
 ## 1.0 (released 2019-09-20)
 ### Added
 * Package `apheleia`

apheleia.el

@@ -362,7 +362,11 @@ as its sole argument."
   "Run a code formatter on the current buffer.
 The formatter is specified by COMMAND, a list of strings or
 symbols (see `apheleia-format-buffer'). Invoke CALLBACK with one
-argument, a buffer containing the output of the formatter."
+argument, a buffer containing the output of the formatter.
+
+If COMMAND uses the symbol `file' and the current buffer is
+modified from what is written to disk, then don't do anything."
+  (cl-block nil
     (let ((input-fname nil)
           (output-fname nil)
           (npx nil))
@@ -373,7 +377,8 @@ argument, a buffer containing the output of the formatter."
         (error "Command cannot start with %S" (car command)))
       (when npx
         (when-let ((project-dir
-                  (locate-dominating-file default-directory "node_modules")))
+                    (locate-dominating-file
+                     default-directory "node_modules")))
           (let ((binary
                  (expand-file-name
                   (car command)
@@ -387,7 +392,9 @@ argument, a buffer containing the output of the formatter."
       (when (memq 'file command)
         (setq command (mapcar (lambda (arg)
                                 (if (eq arg 'file)
-                                  buffer-file-name
+                                    (prog1 buffer-file-name
+                                      (when (buffer-modified-p)
+                                        (cl-return)))
                                   arg))
                               command)))
       (when (memq 'input command)
@@ -417,7 +424,7 @@ argument, a buffer containing the output of the formatter."
                    (when output-fname
                      (erase-buffer)
                      (insert-file-contents-literally output-fname))
-                 (funcall callback stdout)))))
+                   (funcall callback stdout))))))
 
 (defcustom apheleia-formatters
   '((black . ("black" "-"))