Allow context to be set via call (#821)

This PR is doing more than one thing 🙈

If you want me to split this up, let me know. But in addition to
allowing `context` to be passed via `call`, I've also moved where
`view_context` is stored. It's now inside of the `Phlex::Context`
instead of in an ivar of SGML.

I think that ultimately, `view_context` as a concept can be fully
removed from Phlex, and only defined in phlex-rails which is the only
place it gets used. But as I went down that path the changes got more
and more complicated. `phlex-rails` then needs to redefine `call`, which
means it needs to be tightly coupled to `phlex`'s definition of
`call`... it got messy.

Let me know what you think, and if you want me to leave `@_view_context`
alone, that's fine too. I'll open a sibling PR over on phlex-rails to
coincide with this change.

lib/phlex/context.rb

@@ -2,18 +2,19 @@
 
 # @api private
 class Phlex::Context
-	def initialize(user_context = {})
+	def initialize(user_context: {}, view_context: nil)
 		@buffer = +""
 		@capturing = false
 		@user_context = user_context
 		@fragments = nil
 		@in_target_fragment = false
 		@halt_signal = nil
+		@view_context = view_context
 	end
 
 	attr_accessor :buffer, :capturing, :user_context, :in_target_fragment
 
-	attr_reader :fragments
+	attr_reader :fragments, :view_context
 
 	def target_fragments(fragments)
 		@fragments = fragments.to_h { |it| [it, true] }

lib/phlex/sgml.rb

@@ -67,17 +67,16 @@ def to_proc
 		proc { |c| c.render(self) }
 	end
 
-	def call(buffer = +"", context: Phlex::Context.new, view_context: nil, parent: nil, fragments: nil, &block)
+	def call(buffer = +"", context: {}, view_context: nil, parent: nil, fragments: nil, &block)
 		@_buffer = buffer
-		@_context = context
-		@_view_context = view_context
+		@_context = phlex_context = parent&.__context__ || Phlex::Context.new(user_context: context, view_context:)
 		@_parent = parent
 
 		raise Phlex::DoubleRenderError.new("You can't render a #{self.class.name} more than once.") if @_rendered
 		@_rendered = true
 
 		if fragments
-			@_context.target_fragments(fragments)
+			phlex_context.target_fragments(fragments)
 		end
 
 		block ||= @_content_block
@@ -89,7 +88,7 @@ def call(buffer = +"", context: Phlex::Context.new, view_context: nil, parent: n
 			Fiber[:__phlex_component__] = self
 		end
 
-		@_context.around_render do
+		phlex_context.around_render do
 			before_template(&block)
 
 			around_template do
@@ -113,10 +112,12 @@ def call(buffer = +"", context: Phlex::Context.new, view_context: nil, parent: n
 			if Phlex::SUPPORTS_FIBER_STORAGE
 				Fiber[:__phlex_component__] = original_fiber_storage
 			end
-			buffer << context.buffer
+			buffer << phlex_context.buffer
 		end
 	end
 
+	protected def __context__ = @_context
+
 	def context
 		@_context.user_context
 	end
@@ -205,10 +206,10 @@ def flush
 	def render(renderable = nil, &)
 		case renderable
 		when Phlex::SGML
-			renderable.call(@_buffer, context: @_context, view_context: @_view_context, parent: self, &)
+			renderable.call(@_buffer, parent: self, &)
 		when Class
 			if renderable < Phlex::SGML
-				renderable.new.call(@_buffer, context: @_context, view_context: @_view_context, parent: self, &)
+				renderable.new.call(@_buffer, parent: self, &)
 			end
 		when Enumerable
 			renderable.each { |r| render(r, &) }