Use in-tree clang-format-diff.py as Arcanist linter

[scott.linder]

Summary

The only guarantee there seems to be in the clang-format packaging is
that an executable called clang-format is in the PATH. Use the
in-tree clang-format-diff.py to avoid assuming anything else.

Also remove dead code for SVN repo.

[scott.linder]

Switch to git diff-index plumbing command

[mehdi_amini]

Thanks, it seems to work for me

[scott.linder]

I'm going to commit this, as I think it is not a regression from what we already have, but I think the suggestion in another review that Python would be the more portable approach is a reasonable one. If I have some time I may attempt it myself.

utils/arcanist/clang-format.sh

 #!/bin/bash
 
 set -euo pipefail
 
 # "script-and-regex.regex": "/^(?P<severity>.*?)\n(?P<message>.*?)\n(?P<line>\\d),(?P<char>\\d)(\n(?P<original>.*?)>>>>\n(?P<replacement>.*?)<<<<?)$/s",
 
-# Arcanist linter that invokes clang-format.
+# Arcanist linter that invokes clang-format via clang/tools/clang-format/clang-format-diff.py
 # stdout from this script is parsed into a regex and used by Arcanist.
 # https://secure.phabricator.com/book/phabricator/article/arcanist_lint_script_and_regex/
 
 # To skip running all linters when creating/updating a diff, use `arc diff --nolint`.
 
-if ! hash clang-format-diff >/dev/null; then
-  # advice severity level is completely non-disruptive.
-  # switch to warning or error if you want to prompt the user.
+if ! hash clang-format >/dev/null; then
   echo "advice"
-  echo "clang-format-diff not found in user's PATH; not linting file."
+  echo "clang-format not found in user's PATH; not linting file."
+  echo "===="
+  exit 0
+fi
+if ! git rev-parse --git-dir >/dev/null; then
+  echo "advice"
+  echo "not in git repostitory; not linting file."
   echo "===="
   exit 0
 fi
 
 src_file="${1}"
 original_file="$(mktemp)"
 formatted_file="$(mktemp)"
 readonly src_file
 readonly original_file
 readonly formatted_file
 cp -p "${src_file}" "${original_file}"
 cp -p "${src_file}" "${formatted_file}"
 
 cleanup() {
   rc=$?
   rm "${formatted_file}" "${original_file}"
   exit ${rc}
 }
 trap 'cleanup' INT HUP QUIT TERM EXIT
 
 # Arcanist can filter out lint messages for unchanged lines, but for that, we
 # need to generate line by line lint messages. Instead, we generate one lint
-# message on line 1, char 1 with file content edited using clang-format-diff.
-if git rev-parse --git-dir >/dev/null; then
-  arc_base_commit=$(arc which --show-base)
-  # An alternative is to use git-clang-format.
-  git diff -U0 --no-color "${arc_base_commit}"| clang-format-diff -style file -i -p1
-else
-  svn diff --diff-cmd=diff -x -U0 "${src_file}" | clang-format-diff -style LLVM -i
-fi
+# message on line 1, char 1 with file content edited using clang-format-diff.py
+#
+# We do not use git-clang-format because it wants to modify the index,
+# and arc is already holding the lock.
+#
+# We do not look for clang-format-diff or clang-format-diff.py in the PATH
+# because whether/how these are installed differs between distributions,
+# and we have an executable copy in the tree anyway.
+git diff -U0 --no-color "${arc_base_commit}" \
+  | clang/tools/clang-format/clang-format-diff.py -style file -i -p1
 
 cp -p "${src_file}" "${formatted_file}"
 cp -p "${original_file}" "${src_file}"
 if ! diff -q "${src_file}" "${formatted_file}" > /dev/null ; then
   echo "autofix"
   echo "clang-format suggested style edits found:"
   echo "1,1"  # line,char of start of replacement.
   cat "${src_file}"
   echo ">>>>"
   cat "${formatted_file}"
   echo "<<<<"
 fi