Elixir format when elixir installed with asdf (#438)

* Make the formatting tests pass

* Execute mix directly to format buffer

When you use a version manager, the executable `mix` can be a shim of
the real elixir script `mix`, in this case running `elixir mix`
doesn't work and running `mix` directly (which is found with
`executable-find`) is the only option.

Fixes #431
Fixes #435

Author: gabrielelana

elixir-format.el

@@ -84,17 +84,25 @@
     (setq buffer-read-only nil)
     (erase-buffer)))
 
+(defun elixir-format--target-file-name ()
+  "Returns the file name of current visited file.
+
+If the buffer is not visiting any file (like during tests) then
+it returns a file name based on the name of the buffer."
+  (or buffer-file-name (concat (secure-hash 'md5 (buffer-name)) ".ex")))
+
 (defun elixir-format--temp-file-path ()
   "Make a temp file in the current directory, because mix format
 applies rules based on path patterns and looks for .formatter.exs
 files in subdirectories."
-  (concat (file-name-sans-extension buffer-file-name)
-          "-emacs-elixir-format."
-          (file-name-extension buffer-file-name)))
+  (let ((target-file-name (elixir-format--target-file-name)))
+    (concat (file-name-sans-extension target-file-name)
+            "-emacs-elixir-format."
+            (file-name-extension target-file-name))))
 
 (defun elixir-format--run-format (called-interactively-p)
   (let ((tmpfile (elixir-format--temp-file-path))
-        (our-elixir-format-arguments (list (elixir-format--mix-executable) "format")))
+        (our-elixir-format-arguments (list "format")))
 
     (write-region nil nil tmpfile)
     (run-hooks 'elixir-format-hook)
@@ -103,7 +111,7 @@ files in subdirectories."
       (setq our-elixir-format-arguments (append our-elixir-format-arguments elixir-format-arguments)))
     (setq our-elixir-format-arguments (append our-elixir-format-arguments (list tmpfile)))
 
-    (if (zerop (elixir-format--from-mix-root (elixir-format--elixir-executable) (elixir-format--errbuff) our-elixir-format-arguments))
+    (if (zerop (elixir-format--from-mix-root (elixir-format--mix-executable) (elixir-format--errbuff) our-elixir-format-arguments))
         (elixir-format--call-format-command tmpfile)
       (elixir-format--failed-to-format called-interactively-p))
     (delete-file tmpfile)
@@ -203,12 +211,12 @@ Shamelessly stolen from go-mode (https://github.com/dominikh/go-mode.el)"
                         (progn (forward-visible-line arg) (point))))))
 
 
-(defun elixir-format--from-mix-root (elixir-path errbuff format-arguments)
+(defun elixir-format--from-mix-root (mix-path errbuff format-arguments)
   "Run mix format where `mix.exs' is located, because mix is
 meant to be run from the project root. Otherwise, run in the
 current directory."
   (let ((original-default-directory default-directory)
-        (mix-dir (locate-dominating-file buffer-file-name "mix.exs")))
+        (mix-dir (locate-dominating-file (elixir-format--target-file-name) "mix.exs")))
 
     (when mix-dir
       (setq default-directory (expand-file-name mix-dir)))
@@ -218,7 +226,7 @@ current directory."
                      (mapconcat 'identity format-arguments " ")))
 
     (let ((result (apply #'call-process
-                         elixir-path nil errbuff nil format-arguments)))
+                         mix-path nil errbuff nil format-arguments)))
       (setq default-directory original-default-directory)
       result)))