Assume filename correctly (#128)

Fixes #108

Co-authored-by: Radon Rosborough <radon@intuitiveexplanations.com>

CHANGELOG.md

@@ -29,6 +29,9 @@ The format is based on [Keep a Changelog].
   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]
+* clang-format doesn't handle filenames correctly by default. Support
+  for guessing the flags from first the file name then the major mode
+  in the case of a temporary buffer was added in [#128]
 
 ### Formatters
 * [elm-format](https://github.com/avh4/elm-format) for Elm ([#100]).
@@ -56,6 +59,7 @@ The format is based on [Keep a Changelog].
 [#123]: https://github.com/radian-software/apheleia/issues/123
 [#124]: https://github.com/radian-software/apheleia/issues/124
 [#125]: https://github.com/radian-software/apheleia/pull/125
+[#126]: https://github.com/radian-software/apheleia/pull/126
 [#127]: https://github.com/radian-software/apheleia/pull/127
 [#128]: https://github.com/radian-software/apheleia/pull/128
 

apheleia.el

@@ -925,7 +925,15 @@ being run, for diagnostic purposes."
   '((bean-format . ("bean-format"))
     (black . ("black" "-"))
     (brittany . ("brittany"))
-    (clang-format . ("clang-format"))
+    (clang-format . ("clang-format"
+                     "-assume-filename"
+                     (or (buffer-file-name)
+                         (cdr (assoc major-mode
+                                     '((c-mode        . ".c")
+                                       (c++-mode      . ".cpp")
+                                       (cuda-mode     . ".cu")
+                                       (protobuf-mode . ".proto"))))
+                         ".c")))
     (dart-format . ("dart" "format"))
     (elm-format . ("elm-format" "--yes" "--stdin"))
     (fish-indent . ("fish_indent"))

test/formatters/apheleia-ft.el

@@ -271,7 +271,9 @@ environment variable, defaulting to all formatters."
                         in-temp-file)
                        (`output
                         out-temp-file)
-                       (_ arg)))
+                       ((guard (stringp arg))
+                        arg)
+                       (_ (eval arg))))
                    command))
             (setq command (delq 'npx command))
             (setq stdout-buffer (get-buffer-create