Make format-diff.sh branch name agnostic (#8731)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/8731

Reviewed By: jay-zhuang

Differential Revision: D30678124

Pulled By: ltamasi

fbshipit-source-id: 0131b6707f0c5d1d887bcd45781623143b5ccae0

build_tools/format-diff.sh

@@ -120,7 +120,7 @@ uncommitted_code=`git diff HEAD`
 
 # If there's no uncommitted changes, we assume user are doing post-commit
 # format check, in which case we'll try to check the modified lines vs. the
-# facebook/rocksdb.git master branch. Otherwise, we'll check format of the
+# facebook/rocksdb.git main branch. Otherwise, we'll check format of the
 # uncommitted code only.
 if [ -z "$uncommitted_code" ]
 then
@@ -128,8 +128,8 @@ then
   [ "$FORMAT_REMOTE" ] || FORMAT_REMOTE="$(git remote -v | grep 'facebook/rocksdb.git' | head -n 1 | cut -f 1)"
   # Fall back on 'origin' if that fails
   [ "$FORMAT_REMOTE" ] || FORMAT_REMOTE=origin
-  # Use master branch from that remote
-  [ "$FORMAT_UPSTREAM" ] || FORMAT_UPSTREAM="$FORMAT_REMOTE/master"
+  # Use main branch from that remote
+  [ "$FORMAT_UPSTREAM" ] || FORMAT_UPSTREAM="$FORMAT_REMOTE/$(git remote show $FORMAT_REMOTE | sed -n '/HEAD branch/s/.*: //p')"
   # Get the common ancestor with that remote branch. Everything after that
   # common ancestor would be considered the contents of a pull request, so
   # should be relevant for formatting fixes.