[EXPERIMENTAL] Add support for ERB snippets and sidecar templates (#867)

This PR adds experimental support for ERB snippets in Phlex components.

Author: joeldrapper

Gemfile

@@ -12,6 +12,8 @@ group :test do
 	gem "selenium-webdriver"
 end
 
+gem "nokogiri"
+
 group :development do
 	gem "rubocop"
 	gem "ruby-lsp"

config/quickdraw.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "nokogiri"
+
 if ENV["COVERAGE"] == "true"
 	require "simplecov"
 

lib/phlex/sgml.rb

@@ -5,6 +5,17 @@ class Phlex::SGML
 	UNSAFE_ATTRIBUTES = Set.new(%w[srcdoc sandbox http-equiv]).freeze
 	REF_ATTRIBUTES = Set.new(%w[href src action formaction lowsrc dynsrc background ping]).freeze
 
+	ERBCompiler = ERB::Compiler.new("<>").tap do |compiler|
+		compiler.pre_cmd    = [""]
+		compiler.put_cmd    = "@_state.buffer.<<"
+		compiler.insert_cmd = "__implicit_output__"
+		compiler.post_cmd   = ["nil"]
+
+		def compiler.add_insert_cmd(out, content)
+			out.push("#{@insert_cmd}((#{content}))")
+		end
+	end
+
 	autoload :Elements, "phlex/sgml/elements"
 	autoload :SafeObject, "phlex/sgml/safe_object"
 	autoload :SafeValue, "phlex/sgml/safe_value"
@@ -29,6 +40,40 @@ def new(*a, **k, &block)
 				super
 			end
 		end
+
+		def erb(method_name, erb = nil, locals: nil, &block)
+			loc = caller_locations(1, 1)[0]
+			path = loc.path.delete_suffix(".rb")
+			file = loc.path
+			line = loc.lineno - 1
+
+			unless erb
+				method_path = "#{path}/#{method_name}.html.erb"
+				sidecar_path = "#{path}.html.erb"
+
+				if File.exist?(method_path)
+					erb = File.read(method_path)
+					file = method_path
+					line = 1
+				elsif method_name == :view_template && File.exist?(sidecar_path)
+					erb = File.read(sidecar_path)
+					file = sidecar_path
+					line = 1
+				else
+					raise Phlex::RuntimeError.new(<<~MESSAGE)
+						No ERB template found for #{method_name}
+					MESSAGE
+				end
+			end
+
+			code, _enc = ERBCompiler.compile(erb)
+
+			class_eval(<<~RUBY, file, line)
+				def #{method_name} #{locals}
+					#{code}
+				end
+			RUBY
+		end
 	end
 
 	def view_template

quickdraw/erb.test.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class Example < Phlex::HTML
+	def initialize
+		@name = "Joel"
+	end
+
+	erb :view_template, <<~ERB
+		<% card do %>
+			<h1>Hello <%= @name %></h1>
+			<%= greeting %>
+		<% end %>
+	ERB
+
+	erb :say_bye, <<~ERB, locals: %(name:)
+		<h2>Goodbye <%= name %></h2>
+	ERB
+
+	def greeting
+		p { "How do you do?" }
+	end
+
+	def card
+		article do
+			yield
+		end
+		say_bye(name: "Joel")
+	end
+end
+
+test do
+	output = Example.call
+
+	assert_equivalent_html output, <<~HTML
+		<article>
+			<h1>Hello Joel</h1>
+			<p>How do you do?</p>
+		</article>
+		<h2>Goodbye Joel</h2>
+	HTML
+end