clang-format: add a script to reformat topics

Utilities/Scripts/clang-format.bash

+#!/usr/bin/env bash
+#=============================================================================
+# Copyright 2015-2016 Kitware, Inc.
+#
+# Licensed 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.
+#=============================================================================
+
+usage='usage: clang-format.bash [<options>] [--]
+
+    --help                     Print usage plus more detailed help.
+
+    --clang-format <tool>      Use given clang-format tool.
+
+    --amend                    Filter files changed by HEAD.
+    --cached                   Filter files locally staged for commit.
+    --modified                 Filter files locally modified from HEAD.
+    --tracked                  Filter files tracked by Git.
+'
+
+help="$usage"'
+Example to format locally modified files:
+
+    Utilities/Scripts/clang-format.bash --modified
+
+Example to format locally modified files staged for commit:
+
+    Utilities/Scripts/clang-format.bash --cached
+
+Example to format files modified by the most recent commit:
+
+    Utilities/Scripts/clang-format.bash --amend
+
+Example to format all files tracked by Git:
+
+    Utilities/Scripts/clang-format.bash --tracked
+
+Example to format the current topic:
+
+    git filter-branch \
+      --tree-filter "Utilities/Scripts/clang-format.bash --tracked" \
+      master..
+'
+
+die() {
+    echo "$@" 1>&2; exit 1
+}
+
+#-----------------------------------------------------------------------------
+
+# Parse command-line arguments.
+clang_format=''
+mode=''
+while test "$#" != 0; do
+    case "$1" in
+    --amend) mode="amend" ;;
+    --cached) mode="cached" ;;
+    --clang-format) shift; clang_format="$1" ;;
+    --help) echo "$help"; exit 0 ;;
+    --modified) mode="modified" ;;
+    --tracked) mode="tracked" ;;
+    --) shift ; break ;;
+    -*) die "$usage" ;;
+    *) break ;;
+    esac
+    shift
+done
+test "$#" = 0 || die "$usage"
+
+# Find a default tool.
+tools='
+  clang-format-8
+  clang-format
+'
+if test "x$clang_format" = "x"; then
+    for tool in $tools; do
+        if type -p "$tool" >/dev/null; then
+            clang_format="$tool"
+            break
+        fi
+    done
+fi
+
+# Verify that we have a tool.
+if ! type -p "$clang_format" >/dev/null; then
+    echo "Unable to locate '$clang_format'"
+    exit 1
+fi
+
+# Select listing mode.
+case "$mode" in
+    '')       echo "$usage"; exit 0 ;;
+    amend)    git_ls='git diff-tree  --diff-filter=AM --name-only HEAD -r --no-commit-id' ;;
+    cached)   git_ls='git diff-index --diff-filter=AM --name-only HEAD --cached' ;;
+    modified) git_ls='git diff-index --diff-filter=AM --name-only HEAD' ;;
+    tracked)  git_ls='git ls-files' ;;
+    *) die "invalid mode: $mode" ;;
+esac
+
+# List files as selected above.
+$git_ls |
+
+  # Select sources with our attribute.
+  git check-attr --stdin format.clang-format |
+    sed -n '/: format\.clang-format: \(set\|8\)$/ {s/:[^:]*:[^:]*$//p}'  |
+
+  # Update sources in-place.
+  xargs -d '\n' "$clang_format" -i