clang-format: Add a fallback style to Emacs mode

Summary:
This allows one to enable `clang-format-buffer` on file save and avoid
reformatting files that are outside of any project with .clang-format style.

Reviewers: djasper, klimek, sammccall, owenpan, mitchell-stellar, MyDeveloperDay

Reviewed By: MyDeveloperDay

Subscribers: cfe-commits

Patch By: dottedmag

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D69752

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/tools/clang-format/clang-format.el b/clang/tools/clang-format/clang-format.el
index 3096ec12f55..768acb3a5d0 100644
--- a/clang/tools/clang-format/clang-format.el
+++ b/clang/tools/clang-format/clang-format.el
@@ -57,6 +57,18 @@ of the buffer."
   :safe #'stringp)
 (make-variable-buffer-local 'clang-format-style)
 
+(defcustom clang-format-fallback-style "none"
+  "Fallback style to pass to clang-format.
+
+This style will be used if clang-format-style is set to \"file\"
+and no .clang-format is found in the directory of the buffer or
+one of parent directories. Set to \"none\" to disable formatting
+in such buffers."
+  :group 'clang-format
+  :type 'string
+  :safe #'stringp)
+(make-variable-buffer-local 'clang-format-fallback-style)
+
 (defun clang-format--extract (xml-node)
   "Extract replacements and cursor information from XML-NODE."
   (unless (and (listp xml-node) (eq (xml-node-name xml-node) 'replacements))
@@ -162,6 +174,7 @@ uses the function `buffer-file-name'."
                                ,@(and assume-file-name
                                       (list "-assume-filename" assume-file-name))
                                ,@(and style (list "-style" style))
+                               "-fallback-style" ,clang-format-fallback-style
                                "-offset" ,(number-to-string file-start)
                                "-length" ,(number-to-string (- file-end file-start))
                                "-cursor" ,(number-to-string cursor))))