Stick clang-format version to 11 and add back docker-format.sh (apache#45)

* Stick clang-format version to 11 and add back docker-format.sh

### Motivation

Currently the code is formatted by `clang-format` 11. If it's formatted
by other versions of `clang-format`, the style might be a little
different.

### Modifications

- Add back `docker-format.sh` and the associated `Dockerfile.format`.
  This script build the image with `python3` and `clang-format-11`
  installed and the entrypoint is formatting the code.
- Explain the `clang-format` version in README.

* Move Dockerfile and docker-format.sh to build-support

Author: BewareMyPower

README.md

@@ -222,6 +222,8 @@ cd tests
 
 ## Requirements for Contributors
 
-It's required to install [LLVM](https://llvm.org/builds/) for `clang-tidy` and `clang-format`. Pulsar C++ client use `clang-format` 6.0+ to format files.  `make format` automatically formats the files.
+It's required to install [LLVM](https://llvm.org/builds/) for `clang-tidy` and `clang-format`. Pulsar C++ client use `clang-format` **11** to format files.  `make format` automatically formats the files.
+
+For Ubuntu users, you can install `clang-format-11` via `apt install clang-format-11`. For other users, run `./build-support/docker-format.sh` if you have Docker installed.
 
 We welcome contributions from the open source community, kindly make sure your changes are backward compatible with GCC 4.8 and Boost 1.53.

build-support/Dockerfile.format

@@ -0,0 +1,35 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+
+FROM ubuntu:20.04
+
+WORKDIR /app
+
+RUN apt update -y && apt install -y python3 clang-format-11
+ENTRYPOINT ["python3", "./build-support/run_clang_format.py", \
+    "clang-format-11", \
+    "0", \
+    "./build-support/clang_format_exclusions.txt", \
+    "./lib", \
+    "./perf", \
+    "./examples", \
+    "./tests", \
+    "./include", \
+    "./wireshark"]

build-support/docker-format.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+ROOT_DIR=$(git rev-parse --show-toplevel)
+cd $ROOT_DIR/build-support
+
+IMAGE_NAME=apachepulsar/cpp-client-format
+docker image inspect apachepulsar/cpp-client-format 1>/dev/null 2>&1
+OK=$?
+set -e
+if [[ $OK -ne 0 ]]; then
+    echo "The image $IMAGE_NAME doesn't exist, build it"
+    docker build -t $IMAGE_NAME -f ./Dockerfile.format .
+fi
+docker run -v $ROOT_DIR:/app --rm $IMAGE_NAME

cmake_modules/FindClangTools.cmake

@@ -82,8 +82,8 @@ if (CLANG_FORMAT_VERSION)
     endif()
 else()
     find_program(CLANG_FORMAT_BIN
-            NAMES clang-format-5
-            clang-format-5.0
+            NAMES clang-format-11
+            clang-format-11.0
             clang-format
             PATHS ${CLANG_SEARCH_PATHS}
             NO_DEFAULT_PATH