[clang] [emacs][clang-format] Add elisp API for clang-format on git diffs (PR #112792)

[Campbell Barton via cfe-commits]

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@@ -132,18 +132,97 @@ is a zero-based file offset, assuming ‘utf-8-unix’ coding."
     (lambda (byte &optional _quality _coding-system)
       (byte-to-position (1+ byte)))))
 
-;;;###autoload
-(defun clang-format-region (start end &optional style assume-file-name)
-  "Use clang-format to format the code between START and END according to STYLE.
-If called interactively uses the region or the current statement if there is no
-no active region. If no STYLE is given uses `clang-format-style'. Use
-ASSUME-FILE-NAME to locate a style config file, if no ASSUME-FILE-NAME is given
-uses the function `buffer-file-name'."
-  (interactive
-   (if (use-region-p)
-       (list (region-beginning) (region-end))
-     (list (point) (point))))
+(defun clang-format--git-diffs-get-diff-lines (file-orig file-new)
+  "Return all line regions that contain diffs between FILE-ORIG and
+FILE-NEW.  If there is no diff 'nil' is returned. Otherwise the
+return is a 'list' of lines in the format '--lines=<start>:<end>'
+which can be passed directly to 'clang-format'"
+  ;; Temporary buffer for output of diff.
+  (with-temp-buffer
+    (let ((status (call-process
+                   "diff"
+                   nil
+                   (current-buffer)
+                   nil
+                   ;; Binary diff has different behaviors that we
+                   ;; aren't interested in.
+                   "-a"
+                   ;; Printout changes as only the line groups.
+                   "--changed-group-format=--lines=%dF:%dL "
+                   ;; Ignore unchanged content.
+                   "--unchanged-group-format="
+                   file-orig
+                   file-new
+                   )
+                  )
+          (stderr (concat (if (zerop (buffer-size)) "" ": ")
+                          (buffer-substring-no-properties
+                           (point-min) (line-end-position)))))
+      (when (stringp status)
+        (error "(diff killed by signal %s%s)" status stderr))
+      (unless (= status 0)
+        (unless (= status 1)
+          (error "(diff returned unsuccessfully %s%s)" status stderr)))
+
+
+      (if (= status 0)
+          ;; Status == 0 -> no Diff.
+          nil
+        (progn
+          ;; Split "--lines=<S0>:<E0>... --lines=<SN>:<SN>" output to
+          ;; a list for return.
+          (s-split
+           " "
+           (string-trim
+            (buffer-substring-no-properties
+             (point-min) (point-max)))))))))
+
+(defun clang-format--git-diffs-get-git-head-file ()
+  "Returns a temporary file with the content of 'buffer-file-name' at
+git revision HEAD. If the current buffer is either not a file or not
+in a git repo, this results in an error"
+  ;; Needs current buffer to be a file
+  (unless (buffer-file-name)
+    (error "Buffer is not visiting a file"))
+  ;; Need to be able to find version control (git) root
+  (unless (vc-root-dir)
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ideasman42 wrote:

\*picky\* assign this to a variable and reuse it instead of calling twice.

https://github.com/llvm/llvm-project/pull/112792