Git: Add custom merge driver for Rails db/schema.rb

The Rails schema file is notorious for causing merge conflicts, as the order
of some of the lines seems to change randomly. This custom merge driver will
be applied to only Rails schema files, and should prevent merge conflicts.

As suggested by https://nuclearsquid.com/writings/git-tricks-tips-workflows/.

gitattributes

@@ -0,0 +1 @@
+db/schema.rb merge=railsschema

gitconfig

@@ -18,6 +18,16 @@
 [merge]
 	tool = opendiff
 	summary = true
+[merge "railsschema"]
+	name = newer Rails schema version
+	driver = "ruby -e '\n\
+		system %(git), %(merge-file), %(--marker-size=%L), %(%A), %(%O), %(%B)\n\
+		b = File.read(%(%A))\n\
+		b.sub!(/^<+ .*\\nActiveRecord::Schema\\.define.:version => (\\d+). do\\n=+\\nActiveRecord::Schema\\.define.:version => (\\d+). do\\n>+ .*/) do\n\
+		%(ActiveRecord::Schema.define(:version => #{[$1, $2].max}) do)\n\
+		end\n\
+		File.open(%(%A), %(w)) {|f| f.write(b)}\n\
+		exit 1 if b.include?(%(<)*%L)'"
 [help]
 	autocorrect = 50  # Automatically correct misspelled git subcommands after 5 seconds.
 [branch]

install.sh

@@ -50,6 +50,7 @@ ln -sf config_files/jshintrc          ~/.jshintrc
 
 ln -sf config_files/gitconfig         ~/.gitconfig
 ln -sf config_files/gitignore         ~/.gitignore
+ln -sf config_files/gitattributes     ~/.gitattributes
 
 ln -sf config_files/inputrc           ~/.inputrc