Add concept of Liquid::Environment (#1815)

* Add concept of `Liquid::World`

* Rename `World` to `Environment`

README.md

@@ -52,6 +52,47 @@ For standard use you can just pass it the content of a file and call render with
 @template.render('name' => 'tobi')                # => "hi tobi"
 ```
 
+### Concept of Environments
+
+In Liquid, a "Environment" is a scoped environment that encapsulates custom tags, filters, and other configurations. This allows you to define and isolate different sets of functionality for different contexts, avoiding global overrides that can lead to conflicts and unexpected behavior.
+
+By using environments, you can:
+
+1. **Encapsulate Logic**: Keep the logic for different parts of your application separate.
+2. **Avoid Conflicts**: Prevent custom tags and filters from clashing with each other.
+3. **Improve Maintainability**: Make it easier to manage and understand the scope of customizations.
+4. **Enhance Security**: Limit the availability of certain tags and filters to specific contexts.
+
+We encourage the use of Environments over globally overriding things because it promotes better software design principles such as modularity, encapsulation, and separation of concerns.
+
+Here's an example of how you can define and use Environments in Liquid:
+
+```ruby
+user_environment = Liquid::Environment.build do |environment|
+  environment.register_tag("renderobj", RenderObjTag)
+end
+
+Liquid::Template.parse(<<~LIQUID, environment: user_environment)
+  {% renderobj src: "path/to/model.obj" %}
+LIQUID
+```
+
+In this example, `RenderObjTag` is a custom tag that is only available within the `user_environment`.
+
+Similarly, you can define another environment for a different context, such as email templates:
+
+```ruby
+email_environment = Liquid::Environment.build do |environment|
+  environment.register_tag("unsubscribe_footer", UnsubscribeFooter)
+end
+
+Liquid::Template.parse(<<~LIQUID, environment: email_environment)
+  {% unsubscribe_footer %}
+LIQUID
+```
+
+By using Environments, you ensure that custom tags and filters are only available in the contexts where they are needed, making your Liquid templates more robust and easier to manage.
+
 ### Error Modes
 
 Setting the error mode of Liquid lets you specify how strictly you want your templates to be interpreted.
@@ -62,9 +103,10 @@ Liquid also comes with a stricter parser that can be used when editing templates
 when templates are invalid. You can enable this new parser like this:
 
 ```ruby
-Liquid::Template.error_mode = :strict # Raises a SyntaxError when invalid syntax is used
-Liquid::Template.error_mode = :warn # Adds strict errors to template.errors but continues as normal
-Liquid::Template.error_mode = :lax # The default mode, accepts almost anything.
+Liquid::Environment.default.error_mode = :strict
+Liquid::Environment.default.error_mode = :strict # Raises a SyntaxError when invalid syntax is used
+Liquid::Environment.default.error_mode = :warn # Adds strict errors to template.errors but continues as normal
+Liquid::Environment.default.error_mode = :lax # The default mode, accepts almost anything.
 ```
 
 If you want to set the error mode only on specific templates you can pass `:error_mode` as an option to `parse`:

lib/liquid.rb

@@ -50,7 +50,18 @@ module Liquid
 end
 
 require "liquid/version"
+require "liquid/deprecations"
+require "liquid/const"
+require "liquid/template/tag_registry"
+require 'liquid/standardfilters'
+require 'liquid/file_system'
+require 'liquid/parser_switching'
+require 'liquid/tag'
+require 'liquid/block'
 require 'liquid/parse_tree_visitor'
+require 'liquid/interrupts'
+require 'liquid/tags'
+require "liquid/environment"
 require 'liquid/lexer'
 require 'liquid/parser'
 require 'liquid/i18n'
@@ -64,20 +75,14 @@ require 'liquid/strainer_template'
 require 'liquid/strainer_factory'
 require 'liquid/expression'
 require 'liquid/context'
-require 'liquid/parser_switching'
 require 'liquid/tag'
-require 'liquid/tag/disabler'
-require 'liquid/tag/disableable'
-require 'liquid/block'
 require 'liquid/block_body'
 require 'liquid/document'
 require 'liquid/variable'
 require 'liquid/variable_lookup'
 require 'liquid/range_lookup'
-require 'liquid/file_system'
 require 'liquid/resource_limits'
 require 'liquid/template'
-require 'liquid/standardfilters'
 require 'liquid/condition'
 require 'liquid/utils'
 require 'liquid/tokenizer'
@@ -86,7 +91,3 @@ require 'liquid/partial_cache'
 require 'liquid/usage'
 require 'liquid/registers'
 require 'liquid/template_factory'
-
-# Load all the tags of the standard library
-#
-Dir["#{__dir__}/liquid/tags/*.rb"].each { |f| require f }

lib/liquid/block_body.rb

@@ -52,7 +52,7 @@ module Liquid
             next parse_liquid_tag(markup, parse_context)
           end
 
-          unless (tag = registered_tags[tag_name])
+          unless (tag = parse_context.environment.tag_for_name(tag_name))
             # end parsing if we reach an unknown tag and let the caller decide
             # determine how to proceed
             return yield tag_name, markup
@@ -147,7 +147,7 @@ module Liquid
             next
           end
 
-          unless (tag = registered_tags[tag_name])
+          unless (tag = parse_context.environment.tag_for_name(tag_name))
             # end parsing if we reach an unknown tag and let the caller decide
             # determine how to proceed
             return yield tag_name, markup
@@ -262,9 +262,5 @@ module Liquid
     def raise_missing_variable_terminator(token, parse_context)
       BlockBody.raise_missing_variable_terminator(token, parse_context)
     end
-
-    def registered_tags
-      Template.tags
-    end
   end
 end

lib/liquid/const.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Liquid
+  module Const
+    EMPTY_HASH = {}.freeze
+    EMPTY_ARRAY = [].freeze
+  end
+end

lib/liquid/context.rb

@@ -15,14 +15,15 @@ module Liquid
   #   context['bob']  #=> nil  class Context
   class Context
     attr_reader :scopes, :errors, :registers, :environments, :resource_limits, :static_registers, :static_environments
-    attr_accessor :exception_renderer, :template_name, :partial, :global_filter, :strict_variables, :strict_filters
+    attr_accessor :exception_renderer, :template_name, :partial, :global_filter, :strict_variables, :strict_filters, :environment
 
     # rubocop:disable Metrics/ParameterLists
-    def self.build(environments: {}, outer_scope: {}, registers: {}, rethrow_errors: false, resource_limits: nil, static_environments: {}, &block)
+    def self.build(environment: Environment.default, environments: {}, outer_scope: {}, registers: {}, rethrow_errors: false, resource_limits: nil, static_environments: {}, &block)
       new(environments, outer_scope, registers, rethrow_errors, resource_limits, static_environments, &block)
     end
 
-    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, static_environments = {})
+    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, static_environments = {}, environment = Environment.default)
+      @environment = environment
       @environments = [environments]
       @environments.flatten!
 
@@ -32,7 +33,7 @@ module Liquid
       @errors              = []
       @partial             = false
       @strict_variables    = false
-      @resource_limits     = resource_limits || ResourceLimits.new(Template.default_resource_limits)
+      @resource_limits     = resource_limits || ResourceLimits.new(environment.default_resource_limits)
       @base_scope_depth    = 0
       @interrupts          = []
       @filters             = []
@@ -40,10 +41,10 @@ module Liquid
       @disabled_tags       = {}
 
       @registers.static[:cached_partials] ||= {}
-      @registers.static[:file_system] ||= Liquid::Template.file_system
+      @registers.static[:file_system] ||= environment.file_system
       @registers.static[:template_factory] ||= Liquid::TemplateFactory.new
 
-      self.exception_renderer = Template.default_exception_renderer
+      self.exception_renderer = environment.exception_renderer
       if rethrow_errors
         self.exception_renderer = Liquid::RAISE_EXCEPTION_LAMBDA
       end
@@ -60,7 +61,7 @@ module Liquid
     end
 
     def strainer
-      @strainer ||= StrainerFactory.create(self, @filters)
+      @strainer ||= @environment.create_strainer(self, @filters)
     end
 
     # Adds filters to this context.

lib/liquid/deprecations.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "set"
+
+module Liquid
+  class Deprecations
+    class << self
+      attr_accessor :warned
+
+      Deprecations.warned = Set.new
+
+      def warn(name, alternative)
+        return if warned.include?(name)
+
+        warned << name
+
+        caller_location = caller_locations(2, 1).first
+        Warning.warn("[DEPRECATION] #{name} is deprecated. Use #{alternative} instead. Called from #{caller_location}\n")
+      end
+    end
+  end
+end

lib/liquid/environment.rb

@@ -0,0 +1,159 @@
+# frozen_string_literal: true
+
+module Liquid
+  # The Environment is the container for all configuration options of Liquid, such as
+  # the registered tags, filters, and the default error mode.
+  class Environment
+    # The default error mode for all templates. This can be overridden on a
+    # per-template basis.
+    attr_accessor :error_mode
+
+    # The tags that are available to use in the template.
+    attr_accessor :tags
+
+    # The strainer template which is used to store filters that are available to
+    # use in templates.
+    attr_accessor :strainer_template
+
+    # The exception renderer that is used to render exceptions that are raised
+    # when rendering a template
+    attr_accessor :exception_renderer
+
+    # The default file system that is used to load templates from.
+    attr_accessor :file_system
+
+    # The default resource limits that are used to limit the resources that a
+    # template can consume.
+    attr_accessor :default_resource_limits
+
+    class << self
+      # Creates a new environment instance.
+      #
+      # @param tags [Hash] The tags that are available to use in
+      #  the template.
+      # @param file_system The default file system that is used
+      #  to load templates from.
+      # @param error_mode [Symbol] The default error mode for all templates
+      #  (either :strict, :warn, or :lax).
+      # @param exception_renderer [Proc] The exception renderer that is used to
+      #   render exceptions.
+      # @yieldparam environment [Environment] The environment instance that is being built.
+      # @return [Environment] The new environment instance.
+      def build(tags: nil, file_system: nil, error_mode: nil, exception_renderer: nil)
+        ret = new
+        ret.tags = Template::TagRegistry.new(tags) if tags
+        ret.file_system = file_system if file_system
+        ret.error_mode = error_mode if error_mode
+        ret.exception_renderer = exception_renderer if exception_renderer
+        yield ret if block_given?
+        ret.freeze
+      end
+
+      # Returns the default environment instance.
+      #
+      # @return [Environment] The default environment instance.
+      def default
+        @default ||= new
+      end
+
+      # Sets the default environment instance for the duration of the block
+      #
+      # @param environment [Environment] The environment instance to use as the default for the
+      #   duration of the block.
+      # @yield
+      # @return [Object] The return value of the block.
+      def dangerously_override(environment)
+        original_default = @default
+        @default = environment
+        yield
+      ensure
+        @default = original_default
+      end
+    end
+
+    # Initializes a new environment instance.
+    # @api private
+    def initialize
+      @tags = Template::TagRegistry.new(Tags::STANDARD_TAGS)
+      @error_mode = :lax
+      @strainer_template = Class.new(StrainerTemplate).tap do |klass|
+        klass.add_filter(StandardFilters)
+      end
+      @exception_renderer = ->(exception) { exception }
+      @file_system = BlankFileSystem.new
+      @default_resource_limits = Const::EMPTY_HASH
+      @strainer_template_class_cache = {}
+    end
+
+    # Registers a new tag with the environment.
+    #
+    # @param name [String] The name of the tag.
+    # @param klass [Liquid::Tag] The class that implements the tag.
+    # @return [void]
+    def register_tag(name, klass)
+      @tags[name] = klass
+    end
+
+    # Registers a new filter with the environment.
+    #
+    # @param filter [Module] The module that contains the filter methods.
+    # @return [void]
+    def register_filter(filter)
+      @strainer_template_class_cache.clear
+      @strainer_template.add_filter(filter)
+    end
+
+    # Registers multiple filters with this environment.
+    #
+    # @param filters [Array<Module>] The modules that contain the filter methods.
+    # @return [self]
+    def register_filters(filters)
+      @strainer_template_class_cache.clear
+      filters.each { |f| @strainer_template.add_filter(f) }
+      self
+    end
+
+    # Creates a new strainer instance with the given filters, caching the result
+    # for faster lookup.
+    #
+    # @param context [Liquid::Context] The context that the strainer will be
+    #   used in.
+    # @param filters [Array<Module>] The filters that the strainer will have
+    #   access to.
+    # @return [Liquid::Strainer] The new strainer instance.
+    def create_strainer(context, filters = Const::EMPTY_ARRAY)
+      return @strainer_template.new(context) if filters.empty?
+
+      strainer_template = @strainer_template_class_cache[filters] ||= begin
+        klass = Class.new(@strainer_template)
+        filters.each { |f| klass.add_filter(f) }
+        klass
+      end
+
+      strainer_template.new(context)
+    end
+
+    # Returns the names of all the filter methods that are available to use in
+    # the strainer template.
+    #
+    # @return [Array<String>] The names of all the filter methods.
+    def filter_method_names
+      @strainer_template.filter_method_names
+    end
+
+    # Returns the tag class for the given tag name.
+    #
+    # @param name [String] The name of the tag.
+    # @return [Liquid::Tag] The tag class.
+    def tag_for_name(name)
+      @tags[name]
+    end
+
+    def freeze
+      @tags.freeze
+      # TODO: freeze the tags, currently this is not possible because of liquid-c
+      # @strainer_template.freeze
+      super
+    end
+  end
+end

lib/liquid/parse_context.rb

@@ -3,9 +3,10 @@
 module Liquid
   class ParseContext
     attr_accessor :locale, :line_number, :trim_whitespace, :depth
-    attr_reader :partial, :warnings, :error_mode
+    attr_reader :partial, :warnings, :error_mode, :environment
 
-    def initialize(options = {})
+    def initialize(options = Const::EMPTY_HASH)
+      @environment = options.fetch(:environment, Environment.default)
       @template_options = options ? options.dup : {}
 
       @locale   = @template_options[:locale] ||= I18n.new
@@ -35,7 +36,7 @@ module Liquid
       @partial = value
       @options = value ? partial_options : @template_options
 
-      @error_mode = @options[:error_mode] || Template.error_mode
+      @error_mode = @options[:error_mode] || @environment.error_mode
     end
 
     def partial_options

lib/liquid/standardfilters.rb

@@ -1001,6 +1001,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_filter(StandardFilters)
 end

lib/liquid/strainer_factory.rb

@@ -5,37 +5,19 @@ module Liquid
   module StrainerFactory
     extend self
 
-    def add_global_filter(filter)
-      strainer_class_cache.clear
-      GlobalCache.add_filter(filter)
+    def add_global_filter(filter, environment = Environment.default)
+      Deprecations.warn("StrainerFactory.add_global_filter", "Environment#register_filter")
+      environment.register_filter(filter)
     end
 
-    def create(context, filters = [])
-      strainer_from_cache(filters).new(context)
+    def create(context, filters = Const::EMPTY_ARRAY, environment = Environment.default)
+      Deprecations.warn("StrainerFactory.create", "StrainerFactory.create_strainer")
+      environment.create_strainer(context, filters)
     end
 
-    def global_filter_names
-      GlobalCache.filter_method_names
-    end
-
-    GlobalCache = Class.new(StrainerTemplate)
-
-    private
-
-    def strainer_from_cache(filters)
-      if filters.empty?
-        GlobalCache
-      else
-        strainer_class_cache[filters] ||= begin
-          klass = Class.new(GlobalCache)
-          filters.each { |f| klass.add_filter(f) }
-          klass
-        end
-      end
-    end
-
-    def strainer_class_cache
-      @strainer_class_cache ||= {}
+    def global_filter_names(environment = Environment.default)
+      Deprecations.warn("StrainerFactory.global_filter_names", "Environment#filter_method_names")
+      Environment.strainer_template.filter_method_names
     end
   end
 end

lib/liquid/tag.rb

@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+require 'liquid/tag/disabler'
+require 'liquid/tag/disableable'
+
 module Liquid
   class Tag
     attr_reader :nodelist, :tag_name, :line_number, :parse_context

lib/liquid/tags.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require_relative "tags/table_row"
+require_relative "tags/echo"
+require_relative "tags/if"
+require_relative "tags/break"
+require_relative "tags/inline_comment"
+require_relative "tags/for"
+require_relative "tags/assign"
+require_relative "tags/ifchanged"
+require_relative "tags/case"
+require_relative "tags/include"
+require_relative "tags/continue"
+require_relative "tags/capture"
+require_relative "tags/decrement"
+require_relative "tags/unless"
+require_relative "tags/increment"
+require_relative "tags/comment"
+require_relative "tags/raw"
+require_relative "tags/render"
+require_relative "tags/cycle"
+
+module Liquid
+  module Tags
+    STANDARD_TAGS = {
+      'cycle' => Cycle,
+      'render' => Render,
+      'raw' => Raw,
+      'comment' => Comment,
+      'increment' => Increment,
+      'unless' => Unless,
+      'decrement' => Decrement,
+      'capture' => Capture,
+      'continue' => Continue,
+      'include' => Include,
+      'case' => Case,
+      'ifchanged' => Ifchanged,
+      'assign' => Assign,
+      'for' => For,
+      '#' => InlineComment,
+      'break' => Break,
+      'if' => If,
+      'echo' => Echo,
+      'tablerow' => TableRow,
+    }.freeze
+  end
+end

lib/liquid/tags/assign.rb

@@ -72,6 +72,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('assign', Assign)
 end

lib/liquid/tags/break.rb

@@ -26,6 +26,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('break', Break)
 end

lib/liquid/tags/capture.rb

@@ -39,6 +39,4 @@ module Liquid
       true
     end
   end
-
-  Template.register_tag('capture', Capture)
 end

lib/liquid/tags/case.rb

@@ -123,6 +123,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('case', Case)
 end

lib/liquid/tags/comment.rb

@@ -85,6 +85,4 @@ module Liquid
       raise_tag_never_closed("raw")
     end
   end
-
-  Template.register_tag('comment', Comment)
 end

lib/liquid/tags/continue.rb

@@ -17,6 +17,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('continue', Continue)
 end

lib/liquid/tags/cycle.rb

@@ -78,6 +78,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('cycle', Cycle)
 end

lib/liquid/tags/decrement.rb

@@ -35,6 +35,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('decrement', Decrement)
 end

lib/liquid/tags/echo.rb

@@ -36,6 +36,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('echo', Echo)
 end

lib/liquid/tags/for.rb

@@ -201,6 +201,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('for', For)
 end

lib/liquid/tags/if.rb

@@ -135,6 +135,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('if', If)
 end

lib/liquid/tags/ifchanged.rb

@@ -14,6 +14,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('ifchanged', Ifchanged)
 end

lib/liquid/tags/include.rb

@@ -110,6 +110,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('include', Include)
 end

lib/liquid/tags/increment.rb

@@ -35,6 +35,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('increment', Increment)
 end

lib/liquid/tags/inline_comment.rb

@@ -25,6 +25,4 @@ module Liquid
       true
     end
   end
-
-  Template.register_tag('#', InlineComment)
 end

lib/liquid/tags/raw.rb

@@ -56,6 +56,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('raw', Raw)
 end

lib/liquid/tags/render.rb

@@ -108,6 +108,4 @@ module Liquid
       end
     end
   end
-
-  Template.register_tag('render', Render)
 end

lib/liquid/tags/table_row.rb

@@ -91,6 +91,4 @@ module Liquid
       raise Liquid::ArgumentError, "invalid integer"
     end
   end
-
-  Template.register_tag('tablerow', TableRow)
 end

lib/liquid/tags/unless.rb

@@ -44,6 +44,4 @@ module Liquid
       output
     end
   end
-
-  Template.register_tag('unless', Unless)
 end

lib/liquid/template.rb

@@ -18,42 +18,6 @@ module Liquid
     attr_accessor :root, :name
     attr_reader :resource_limits, :warnings
 
-    class TagRegistry
-      include Enumerable
-
-      def initialize
-        @tags  = {}
-        @cache = {}
-      end
-
-      def [](tag_name)
-        return nil unless @tags.key?(tag_name)
-        return @cache[tag_name] if Liquid.cache_classes
-
-        lookup_class(@tags[tag_name]).tap { |o| @cache[tag_name] = o }
-      end
-
-      def []=(tag_name, klass)
-        @tags[tag_name]  = klass.name
-        @cache[tag_name] = klass
-      end
-
-      def delete(tag_name)
-        @tags.delete(tag_name)
-        @cache.delete(tag_name)
-      end
-
-      def each(&block)
-        @tags.each(&block)
-      end
-
-      private
-
-      def lookup_class(name)
-        Object.const_get(name)
-      end
-    end
-
     attr_reader :profiler
 
     class << self
@@ -61,46 +25,71 @@ module Liquid
       # :lax acts like liquid 2.5 and silently ignores malformed tags in most cases.
       # :warn is the default and will give deprecation warnings when invalid syntax is used.
       # :strict will enforce correct syntax.
-      attr_accessor :error_mode
-      Template.error_mode = :lax
-
-      attr_accessor :default_exception_renderer
-      Template.default_exception_renderer = lambda do |exception|
-        exception
+      def error_mode=(mode)
+        Deprecations.warn("Template.error_mode=", "Environment#error_mode=")
+        Environment.default.error_mode = mode
       end
 
-      attr_accessor :file_system
-      Template.file_system = BlankFileSystem.new
+      def error_mode
+        Environment.default.error_mode
+      end
 
-      attr_accessor :tags
-      Template.tags = TagRegistry.new
-      private :tags=
+      def default_exception_renderer=(renderer)
+        Deprecations.warn("Template.default_exception_renderer=", "Environment#exception_renderer=")
+        Environment.default.exception_renderer = renderer
+      end
+
+      def default_exception_renderer
+        Environment.default.exception_renderer
+      end
+
+      def file_system=(file_system)
+        Deprecations.warn("Template.file_system=", "Environment#file_system=")
+        Environment.default.file_system = file_system
+      end
+
+      def file_system
+        Environment.default.file_system
+      end
+
+      def tags
+        Environment.default.tags
+      end
 
       def register_tag(name, klass)
-        tags[name.to_s] = klass
+        Deprecations.warn("Template.register_tag", "Environment#register_tag")
+        Environment.default.register_tag(name, klass)
       end
 
       # Pass a module with filter methods which should be available
       # to all liquid views. Good for registering the standard library
       def register_filter(mod)
-        StrainerFactory.add_global_filter(mod)
+        Deprecations.warn("Template.register_filter", "Environment#register_filter")
+        Environment.default.register_filter(mod)
       end
 
-      attr_accessor :default_resource_limits
-      Template.default_resource_limits = {}
-      private :default_resource_limits=
+      private def default_resource_limits=(limits)
+        Deprecations.warn("Template.default_resource_limits=", "Environment#default_resource_limits=")
+        Environment.default.default_resource_limits = limits
+      end
+
+      def default_resource_limits
+        Environment.default.default_resource_limits
+      end
 
       # creates a new <tt>Template</tt> object from liquid source code
       # To enable profiling, pass in <tt>profile: true</tt> as an option.
       # See Liquid::Profiler for more information
       def parse(source, options = {})
-        new.parse(source, options)
+        environment = options[:environment] || Environment.default
+        new(environment: environment).parse(source, options)
       end
     end
 
-    def initialize
+    def initialize(environment: Environment.default)
+      @environment = environment
       @rethrow_errors  = false
-      @resource_limits = ResourceLimits.new(Template.default_resource_limits)
+      @resource_limits = ResourceLimits.new(environment.default_resource_limits)
     end
 
     # Parse source code.
@@ -162,11 +151,11 @@ module Liquid
         c
       when Liquid::Drop
         drop         = args.shift
-        drop.context = Context.new([drop, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits)
+        drop.context = Context.new([drop, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
       when Hash
-        Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
       when nil
-        Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
       else
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end
@@ -226,8 +215,14 @@ module Liquid
       @options      = options
       @profiling    = profiling
       @line_numbers = options[:line_numbers] || @profiling
-      parse_context = options.is_a?(ParseContext) ? options : ParseContext.new(options)
-      @warnings     = parse_context.warnings
+      parse_context = if options.is_a?(ParseContext)
+        options
+      else
+        opts = options.key?(:environment) ? options : options.merge(environment: @environment)
+        ParseContext.new(opts)
+      end
+
+      @warnings = parse_context.warnings
       parse_context
     end
 

lib/liquid/template/tag_registry.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Template
+    class TagRegistry
+      include Enumerable
+
+      def initialize(tags = nil)
+        @tags  = {}
+        @cache = {}
+        tags.each { |tag_name, klass| self[tag_name] = klass }
+        Deprecations.warn("Template::TagRegistry", "Use a Environment instance with zeitwerk")
+      end
+
+      def [](tag_name)
+        return nil unless @tags.key?(tag_name)
+        return @cache[tag_name] if Liquid.cache_classes
+
+        lookup_class(@tags[tag_name]).tap { |o| @cache[tag_name] = o }
+      end
+
+      def delete(tag_name)
+        Deprecations.warn("Template::TagRegistry#delete", "Use a Environment instance with immutable tags")
+        @tags.delete(tag_name)
+        @cache.delete(tag_name)
+      end
+
+      def []=(tag_name, klass)
+        @tags[tag_name]  = klass.name
+        @cache[tag_name] = klass
+      end
+
+      def each(&block)
+        @tags.each(&block)
+      end
+
+      private
+
+      def lookup_class(name)
+        Object.const_get(name)
+      end
+    end
+  end
+end

test/integration/error_handling_test.rb

@@ -219,6 +219,21 @@ class ErrorHandlingTest < Minitest::Test
     Liquid::Template.default_exception_renderer = old_exception_renderer if old_exception_renderer
   end
 
+  def test_setting_exception_renderer_on_environment
+    exceptions = []
+    exception_renderer = ->(e) do
+      exceptions << e
+      ''
+    end
+
+    environment = Liquid::Environment.build(exception_renderer: exception_renderer)
+    template = Liquid::Template.parse('This is a runtime error: {{ errors.argument_error }}', environment: environment)
+    output = template.render('errors' => ErrorDrop.new)
+
+    assert_equal('This is a runtime error: ', output)
+    assert_equal([Liquid::ArgumentError], template.errors.map(&:class))
+  end
+
   def test_exception_renderer_exposing_non_liquid_error
     template   = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)
     exceptions = []
@@ -242,16 +257,10 @@ class ErrorHandlingTest < Minitest::Test
   end
 
   def test_included_template_name_with_line_numbers
-    old_file_system = Liquid::Template.file_system
+    environment = Liquid::Environment.build(file_system: TestFileSystem.new)
+    template = Liquid::Template.parse("Argument error:\n{% include 'product' %}", line_numbers: true, environment: environment)
+    page     = template.render('errors' => ErrorDrop.new)
 
-    begin
-      Liquid::Template.file_system = TestFileSystem.new
-
-      template = Liquid::Template.parse("Argument error:\n{% include 'product' %}", line_numbers: true)
-      page     = template.render('errors' => ErrorDrop.new)
-    ensure
-      Liquid::Template.file_system = old_file_system
-    end
     assert_equal("Argument error:\nLiquid error (product line 1): argument error", page)
     assert_equal("product", template.errors.first.template_name)
   end

test/integration/tags/include_tag_test.rb

@@ -49,14 +49,6 @@ end
 class IncludeTagTest < Minitest::Test
   include Liquid
 
-  def setup
-    @default_file_system = Liquid::Template.file_system
-  end
-
-  def teardown
-    Liquid::Template.file_system = @default_file_system
-  end
-
   def test_include_tag_looks_for_file_system_in_registers_first
     assert_equal(
       'from OtherFileSystem',
@@ -214,9 +206,10 @@ class IncludeTagTest < Minitest::Test
 
   def test_include_tag_caches_second_read_of_same_partial
     file_system = CountingFileSystem.new
+    environment = Liquid::Environment.build(file_system: file_system)
     assert_equal(
       'from CountingFileSystemfrom CountingFileSystem',
-      Template.parse("{% include 'pick_a_source' %}{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system }),
+      Template.parse("{% include 'pick_a_source' %}{% include 'pick_a_source' %}", environment: environment).render!({}, registers: { file_system: file_system }),
     )
     assert_equal(1, file_system.count)
   end

test/test_helper.rb

@@ -42,10 +42,11 @@ module Minitest
       message: nil, partials: nil, error_mode: nil, render_errors: false,
       template_factory: nil
     )
-      template = Liquid::Template.parse(template, line_numbers: true, error_mode: error_mode&.to_sym)
       file_system = StubFileSystem.new(partials || {})
+      environment = Liquid::Environment.build(file_system: file_system)
+      template = Liquid::Template.parse(template, line_numbers: true, error_mode: error_mode&.to_sym, environment: environment)
       registers = Liquid::Registers.new(file_system: file_system, template_factory: template_factory)
-      context = Liquid::Context.build(static_environments: assigns, rethrow_errors: !render_errors, registers: registers)
+      context = Liquid::Context.build(static_environments: assigns, rethrow_errors: !render_errors, registers: registers, environment: environment)
       output = template.render(context)
       assert_equal(expected, output, message)
     end
@@ -78,22 +79,12 @@ module Minitest
       assert_equal(times, calls, "Number of calls to Usage.increment with #{name.inspect}")
     end
 
-    def with_global_filter(*globals)
-      original_global_cache = Liquid::StrainerFactory::GlobalCache
-      Liquid::StrainerFactory.send(:remove_const, :GlobalCache)
-      Liquid::StrainerFactory.const_set(:GlobalCache, Class.new(Liquid::StrainerTemplate))
+    def with_global_filter(*globals, &blk)
+      environment = Liquid::Environment.build do |w|
+        w.register_filters(globals)
+      end
 
-      globals.each do |global|
-        Liquid::Template.register_filter(global)
-      end
-      Liquid::StrainerFactory.send(:strainer_class_cache).clear
-      begin
-        yield
-      ensure
-        Liquid::StrainerFactory.send(:remove_const, :GlobalCache)
-        Liquid::StrainerFactory.const_set(:GlobalCache, original_global_cache)
-        Liquid::StrainerFactory.send(:strainer_class_cache).clear
-      end
+      Environment.dangerously_override(environment, &blk)
     end
 
     def with_error_mode(mode)
@@ -104,18 +95,11 @@ module Minitest
       Liquid::Template.error_mode = old_mode
     end
 
-    def with_custom_tag(tag_name, tag_class)
-      old_tag = Liquid::Template.tags[tag_name]
-      begin
-        Liquid::Template.register_tag(tag_name, tag_class)
-        yield
-      ensure
-        if old_tag
-          Liquid::Template.tags[tag_name] = old_tag
-        else
-          Liquid::Template.tags.delete(tag_name)
-        end
-      end
+    def with_custom_tag(tag_name, tag_class, &block)
+      environment = Liquid::Environment.default.dup
+      environment.register_tag(tag_name, tag_class)
+
+      Environment.dangerously_override(environment, &block)
     end
   end
 end

test/unit/strainer_template_unit_test.rb

@@ -58,8 +58,9 @@ class StrainerTemplateUnitTest < Minitest::Test
 
   def test_add_filter_does_not_raise_when_module_overrides_previously_registered_method
     with_global_filter do
-      strainer = Context.new.strainer
-      strainer.class.add_filter(PublicMethodOverrideFilter)
+      context = Context.new
+      context.add_filters([PublicMethodOverrideFilter])
+      strainer = context.strainer
       assert(strainer.class.send(:filter_methods).include?('public_filter'))
     end
   end

test/unit/template_unit_test.rb

@@ -36,7 +36,6 @@ class TemplateUnitTest < Minitest::Test
     assert(Template.tags['custom'].equal?(original_klass))
   ensure
     Object.send(:remove_const, :CustomTag)
-    Template.tags.delete('custom')
     Liquid.cache_classes = original_cache_setting
   end
 
@@ -46,36 +45,26 @@ class TemplateUnitTest < Minitest::Test
 
     original_klass = Class.new
     Object.send(:const_set, :CustomTag, original_klass)
-    Template.register_tag('custom', CustomTag)
+    with_custom_tag('custom', CustomTag) do
+      Object.send(:remove_const, :CustomTag)
 
-    Object.send(:remove_const, :CustomTag)
+      new_klass = Class.new
+      Object.send(:const_set, :CustomTag, new_klass)
 
-    new_klass = Class.new
-    Object.send(:const_set, :CustomTag, new_klass)
-
-    assert(Template.tags['custom'].equal?(new_klass))
+      assert(Template.tags['custom'].equal?(new_klass))
+    end
   ensure
     Object.send(:remove_const, :CustomTag)
-    Template.tags.delete('custom')
     Liquid.cache_classes = original_cache_setting
   end
 
   class FakeTag; end
 
-  def test_tags_delete
-    Template.register_tag('fake', FakeTag)
-    assert_equal(FakeTag, Template.tags['fake'])
-
-    Template.tags.delete('fake')
-    assert_nil(Template.tags['fake'])
-  end
-
   def test_tags_can_be_looped_over
-    Template.register_tag('fake', FakeTag)
-    result = Template.tags.map { |name, klass| [name, klass] }
-    assert(result.include?(["fake", "TemplateUnitTest::FakeTag"]))
-  ensure
-    Template.tags.delete('fake')
+    with_custom_tag('fake', FakeTag) do
+      result = Template.tags.map { |name, klass| [name, klass] }
+      assert(result.include?(["fake", "TemplateUnitTest::FakeTag"]))
+    end
   end
 
   class TemplateSubclass < Liquid::Template