Add script to merge clang-format changes into branches.

Still needs the hash for the commit that introduces clang-format in master
to actually work.

utils/blender_merge_format_changes.py

+#!/usr/bin/env python3
+
+import os
+import subprocess
+import sys
+
+format_commit = '<clang-format-commit>' # TODO: update with actual commit that applies formatting
+pre_format_commit = format_commit + '~1'
+
+def get_string(cmd):
+    return subprocess.run(cmd, stdout=subprocess.PIPE).stdout.decode('utf8').strip()
+
+# Parse arguments.
+mode = None
+if len(sys.argv) == 2:
+    if sys.argv[1] == '--rebase':
+        mode = 'rebase'
+    elif sys.argv[1] == '--merge':
+        mode = 'merge'
+
+if mode == None:
+    print("Merge or rebase Blender master into a branch in 3 steps,")
+    print("to automatically merge clang-format changes.")
+    print("")
+    print("  --rebase     Perform equivalent of 'git rebase master'")
+    print("  --merge      Perform equivalent of 'git merge master'")
+    sys.exit(0)
+
+# Verify we are in the right directory.
+root_path = get_string(['git', 'rev-parse', '--show-superproject-working-tree'])
+if os.path.realpath(root_path) != os.path.realpath(os.getcwd()):
+    print("BLENDER MERGE: must run from blender repository root directory")
+    sys.exit(1)
+
+# Abort if a rebase is still progress.
+rebase_merge = get_string(['git', 'rev-parse', '--git-path', 'rebase-merge'])
+rebase_apply = get_string(['git', 'rev-parse', '--git-path', 'rebase-apply'])
+merge_head = get_string(['git', 'rev-parse', '--git-path', 'MERGE_HEAD'])
+if os.path.exists(rebase_merge) or \
+   os.path.exists(rebase_apply) or \
+   os.path.exists(merge_head):
+    print("BLENDER MERGE: rebase or merge in progress, complete it first")
+    sys.exit(1)
+
+# Abort if uncommitted changes.
+changes = get_string(['git', 'status', '--porcelain', '--untracked-files=no'])
+if len(changes) != 0:
+    print("BLENDER MERGE: detected uncommitted changes, can't run")
+    sys.exit(1)
+
+# Setup command, with commit message for merge commits.
+if mode == 'rebase':
+    mode_cmd = 'rebase'
+else:
+    branch = get_string(['git', 'rev-parse', '--abbrev-ref', 'HEAD'])
+    mode_cmd = 'merge --no-edit -m "Merge \'master\' into \'' + branch + '\'"';
+
+# Rebase up to the clang-format commit.
+code = os.system('git merge-base --is-ancestor ' + pre_format_commit + ' HEAD')
+if code != 0:
+    code = os.system('git ' + mode_cmd + ' ' + pre_format_commit)
+    if code != 0:
+        print("BLENDER MERGE: resolve conflicts, complete " + mode + " and run again")
+        sys.exit(code)
+
+# Rebase clang-format commit.
+code = os.system('git merge-base --is-ancestor ' + format_commit + ' HEAD')
+if code != 0:
+    os.system('git ' + mode_cmd + ' -Xignore-all-space -Xours ' + format_commit )
+    os.system('make format')
+    os.system('git add -u')
+    count = int(get_string(['git', 'rev-list', '--count', '' + format_commit + '..HEAD']))
+    if count == 1 or mode == 'merge':
+        # Amend if we just have a single commit or are merging.
+        os.system('git commit --amend --no-edit')
+    else:
+        # Otherwise create a commit for formatting.
+        os.system('git commit -m "Cleanup: apply clang format"')
+
+# Rebase remaning commits
+code = os.system('git ' + mode_cmd + ' master')
+if code != 0:
+    print("BLENDER MERGE: resolve conflicts, complete " + mode + " and you're done")
+else:
+    print("BLENDER MERGE: done")
+sys.exit(code)