erbでincompatible character encodingsが出たときの対処（encoding UTF-8を入れる）

環境

• erbを素で使っている（Ruby on Railsは使っていない）

Before

AUTHOR = '結城浩'
AUTHOR_YOMI = 'ゆうき・ひろし'
...

<%
load 'common/author.rb'
COLOR_PRIMARY = '#559fbf'
URL = 'http://girl1.hyuki.net/'
...
%>
...

Error

$ erb index.erb > index.html
... in `concat': incompatible character encodings: ASCII-8BIT and UTF-8 (Encoding::CompatibilityError)

After

# encoding: UTF-8
AUTHOR = '結城浩'
AUTHOR_YOMI = 'ゆうき・ひろし'
...

<%# encoding: UTF-8 %>
<%
load 'common/author.rb'
COLOR_PRIMARY = '#559fbf'
URL = 'http://girl1.hyuki.net/'
...
%>
...

関連

• https://snap.textfile.org/20160214142505/