Guard against missing formatters (#126)

Fixes #122

2 files changed, 26 insertions, 20 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0498d7c..7e89f92 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,10 @@ The format is based on [Keep a Changelog].
   running. Instead, it is disabled in narrowed buffers. Support for
   narrowed buffers may be added in future but it has never been
   correctly supported in the past (see [#43]). More at [#124], [#127].
+* Currently, when a formatter invoked via a process isn't installed
+  correctly; it throws an error. It doesn't make sense to attempt to
+  format if we can't find the correct formatter, so instead formatting
+  is only attempted when the formatter is found. [#126]
 
 ### Formatters
 * [elm-format](https://github.com/avh4/elm-format) for Elm ([#100]).
@@ -53,6 +57,7 @@ The format is based on [Keep a Changelog].
 [#124]: https://github.com/radian-software/apheleia/issues/124
 [#125]: https://github.com/radian-software/apheleia/pull/125
 [#127]: https://github.com/radian-software/apheleia/pull/127
+[#128]: https://github.com/radian-software/apheleia/pull/128
 
 ## 3.0 (released 2022-06-01)
 ### Breaking changes
diff --git a/apheleia.el b/apheleia.el
index 379fd0d..f9dbcc5 100644
--- a/apheleia.el
+++ b/apheleia.el
@@ -862,27 +862,28 @@ purposes."
                                 (locate-library "apheleia"))))))
                         exec-path)))
       (cl-destructuring-bind (input-fname output-fname stdin &rest command) ret
-        (apheleia--execute-formatter-process
-         :command command
-         :stdin (unless input-fname
-                  stdin)
-         :callback
-         (lambda (stdout)
-           (when output-fname
-             ;; Load output-fname contents into the stdout buffer.
-             (erase-buffer)
-             (insert-file-contents-literally output-fname))
-
-           (funcall callback stdout))
-         :ensure
-         (lambda ()
-           (ignore-errors
-             (when input-fname
-               (delete-file input-fname))
+        (when (executable-find (car command))
+          (apheleia--execute-formatter-process
+           :command command
+           :stdin (unless input-fname
+                    stdin)
+           :callback
+           (lambda (stdout)
              (when output-fname
-               (delete-file output-fname))))
-         :remote remote
-         :formatter formatter)))))
+               ;; Load output-fname contents into the stdout buffer.
+               (erase-buffer)
+               (insert-file-contents-literally output-fname))
+
+             (funcall callback stdout))
+           :ensure
+           (lambda ()
+             (ignore-errors
+               (when input-fname
+                 (delete-file input-fname))
+               (when output-fname
+                 (delete-file output-fname))))
+           :remote remote
+           :formatter formatter))))))
 
 (defun apheleia--run-formatter-function
     (func buffer remote callback stdin formatter)