[#232] Format from elixir project dir (#239)

Make it so that if there is a `.formatter.exs` file somewhere in the
parent directories, then Apheleia will run `mix format` from there
instead of the current directory.

Close #232

CHANGELOG.md

@@ -34,6 +34,9 @@ The format is based on [Keep a Changelog].
 * Autoload the apheleia-goto-error command ([#215]).
 * Use `lisp-indent` as default formatter for `emacs-lisp-mode` ([#223])
 * Use `hclfmt` for formatting hashicorp HCL files ([#231])
+* The `mix format` formatter will respect `.formatter.exs` files even
+  if they are present in a parent directory rather than the same
+  directory as the file being formatted ([#232]).
 
 ### Internal Changes
 * Refactored the organisation of the apheleia package for ease of
@@ -104,6 +107,7 @@ The format is based on [Keep a Changelog].
 [#215]: https://github.com/radian-software/apheleia/pull/215
 [#223]: https://github.com/radian-software/apheleia/pull/223
 [#231]: https://github.com/radian-software/apheleia/pull/231
+[#232]: https://github.com/radian-software/apheleia/issues/232
 [#236]: https://github.com/radian-software/apheleia/pull/236
 [#242]: https://github.com/radian-software/apheleia/pull/242
 

apheleia-formatters.el

@@ -73,7 +73,7 @@
     (lisp-indent . apheleia-indent-lisp-buffer)
     (ktlint . ("ktlint" "--log-level=none" "--stdin" "-F" "-"))
     (latexindent . ("latexindent" "--logfile=/dev/null"))
-    (mix-format . ("mix" "format" "-"))
+    (mix-format . ("apheleia-mix" "format" "-"))
     (nixfmt . ("nixfmt"))
     (ocamlformat . ("ocamlformat" "-" "--name" filepath
                     "--enable-outside-detected-project"))

scripts/formatters/apheleia-mix

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# This function prints the name of the current directory if it
+# contains a file or directory named after the first argument, or the
+# parent directory if it contains such a file, or the parent's parent,
+# and so on. If no such file is found it returns nonzero.
+# https://unix.stackexchange.com/a/22215
+find_upwards() {
+    fname="$1"
+
+    path="${PWD}"
+    while [[ -n "${path}" && ! -e "${path}/${fname}" ]]; do
+        path="${path%/*}"
+    done
+    [[ -n "${path}" ]] && echo "${path}"
+}
+
+if dir="$(find_upwards .formatter.exs)"; then
+    cd -- "${dir}" || exit
+fi
+
+exec mix "$@"