git-merge-structure-sql - git merge driver for db/structure.sql of Rails projects

git-merge-structure-sql

#!/usr/bin/env ruby
#
# git-merge-structure-sql - git merge driver for db/structure.sql of Rails projects
#
# How to use:
#     $ git config merge.merge-structure-sql.name 'Rails structure.sql merge driver'
#     $ git config merge.merge-structure-sql.driver 'git-merge-structure-sql %A %O %B'
#
#     # To enable it locally:
#     $ echo 'structure.sql merge=merge-structure-sql' >> .git/info/attributes
#
#     # To enable it globally:
#     $ git config --global core.attributesfile '~/.config/git/attributes'
#     $ echo 'structure.sql merge=merge-structure-sql' >> ~/.config/git/attributes
#
# Copyright (c) 2018 Akinori MUSHA
#
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
#

class StructureSqlMergeDriver
  VARIANTS = []

  module PostgreSQL
    RE_VERSION = /^\('(\d+)'\)[,;]\n/
    RE_VERSIONS = /^INSERT INTO "schema_migrations" \(version\) VALUES\n\K#{RE_VERSION}+/

    class << self
      def match?(content)
        RE_VERSIONS === content
      end

      def merge!(*contents)
        merge_versions!(*contents)
      end

      private

      def merge_versions!(*contents)
        replacement = format_versions(
          contents.inject([]) { |versions, content|
            versions | content[RE_VERSIONS].scan(RE_VERSION).flatten
          }.sort
        )

        contents.each { |content|
          content.sub!(RE_VERSIONS, replacement)
        }
      end

      def format_versions(versions)
        versions.map { |version| "('%s')" % version }.join(",\n") << ";\n"
      end
    end

    VARIANTS << self
  end

  module MySQL
    class << self
      RE_DUMP_TIMESTAMP = /^-- Dump completed on \K.+$/
      RE_AUTO_INCREMENT_VALUE = /^\)(?= ).*\K AUTO_INCREMENT=\d+(?=.*;$)/
      RE_VERSION = /^INSERT INTO schema_migrations \(version\) VALUES \('(\d+)'\);\s+/
      RE_VERSIONS = /#{RE_VERSION}+/

      def match?(content)
        /^-- MySQL dump / === content
      end

      def merge!(*contents)
        merge_dump_timestamps!(*contents)
        scrub_auto_increment_values!(*contents)
        merge_versions!(*contents)
      end

      private

      def merge_dump_timestamps!(*contents)
        replacement = contents.inject('') { |timestamp, content|
          [timestamp, *content.scan(RE_DUMP_TIMESTAMP)].max rescue ''
        }

        unless replacement.empty?
          contents.each { |content|
            content.gsub!(RE_DUMP_TIMESTAMP, replacement)
          }
        end
      end

      def scrub_auto_increment_values!(*contents)
        contents.each { |content|
          content.gsub!(RE_AUTO_INCREMENT_VALUE, '')
        }
      end

      def merge_versions!(*contents)
        replacement = format_versions(
          contents.inject([]) { |versions, content|
            versions | content.scan(RE_VERSION).flatten
          }.sort
        )

        contents.each { |content|
          content.sub!(RE_VERSIONS, replacement)
        }
      end

      def format_versions(versions)
        versions.map { |version| "INSERT INTO schema_migrations (version) VALUES ('%s');\n\n" % version }.join
      end
    end

    VARIANTS << self
  end

  def main(*files)
    contents = files.map { |file| File.read(file) }

    sample = contents[0]
    variant = VARIANTS.find { |v| v.match?(sample) } or
      raise 'unsupported dump file format'

    variant.merge!(*contents)

    files.zip(contents) do |file, content|
      File.write(file, content)
    end

    exec(*%W[git merge-file -q], *files)
  rescue => e
    STDERR.puts "#{$0}: #{e.message}"
    exit 1
  end
end

if $0 == __FILE__
  StructureSqlMergeDriver.new.main(*ARGV)
end

This has been released as a gem: https://github.com/knu/git-merge-structure-sql