rails-merge-db-schema

#!/usr/bin/env ruby
#
# usage: rails-merge-db-schema <current-file> <base-file> <other-file> <marker-size>
#
# install:
#
#    $ git config --global merge.railsschema.name "newer Rails schema version"
#    $ git config --global merge.railsschema.driver "rails-merge-db-schema %A %O %B %L"

exit 1 if ARGV.size != 4
current_file, base_file, other_file, marker_size, _ = ARGV

# perform a standard git merge
system('git', 'merge-file', "--marker-size=#{marker_size}", current_file, base_file, other_file)

# build a regular expression which matches a schema defintion merge
# conflict. Example:
#
#     <<<<<<< .merge_file_p2F2ih
#     ActiveRecord::Schema.define(version: 20161011162735) do
#     =======
#     ActiveRecord::Schema.define(version: 20161006133305) do
#     >>>>>>> .merge_file_nfurhQ
#
MERGE_CONFLICT_START     = /<{#{marker_size}} #{current_file}/
MERGE_CONFLICT_SEPERATOR = /={#{marker_size}}/
MERGE_CONFLICT_END       = />{#{marker_size}} #{other_file}/
SCHEMA_DEFINITION        = /ActiveRecord::Schema\.define\(version: (\d+)\) do/

SCHEMA_DEFINITION_CONFLICT_MATCHER = /
#{MERGE_CONFLICT_START}
#{SCHEMA_DEFINITION}
#{MERGE_CONFLICT_SEPERATOR}
#{SCHEMA_DEFINITION}
#{MERGE_CONFLICT_END}
/

# resolve a schema definition merge conflict by choosing the latest
# version number
merge = File.read(current_file).sub!(SCHEMA_DEFINITION_CONFLICT_MATCHER) do
  a, b = Integer($1), Integer($2)
  latest_version = [a, b].max
  "\nActiveRecord::Schema.define(version: #{latest_version}) do\n"
end

# write the resulting merge back to the current file
File.open(current_file, 'w') do |f|
  f.write(merge)
end

# if there are other merge conflicts remaining, exit with code 1
if merge =~ MERGE_CONFLICT_START
  exit 1
end