What causes "Template.default_exception_renderer=" in Shopify/liquid?

Set Liquid::Environment.default.exception_renderer = renderer

Template.default_exception_renderer=

Error message

Template.default_exception_renderer=

What it means

Setting Liquid::Template.default_exception_renderer= is deprecated; global template defaults moved to Liquid::Environment, and this shim forwards to Environment#exception_renderer= while emitting a deprecation warning.

Solutions

Set Liquid::Environment.default.exception_renderer = renderer
Prefer building a dedicated Environment with its own exception_renderer and pass it to Template.parse

Example fix

// before
Liquid::Template.default_exception_renderer = ->(e) { e.message }
// after
Liquid::Environment.default.exception_renderer = ->(e) { e.message }

Defensive patterns

Strategy: validation

Validate before calling

env = Liquid::Environment.default
env.exception_renderer = renderer # configure via Environment, not Template

Prevention

Centralize Liquid configuration in one initializer that only uses Environment
Fail tests when any Liquid deprecation warning appears
Avoid assigning to Template class-level setters in gems/engines

When it happens

Trigger: Calling Liquid::Template.default_exception_renderer = ->(e){ ... } in an initializer or test setup.

Common situations: Apps upgrading from Liquid 4-era global configuration; centralizers that render templates with custom error handling per environment.

Understand the failure class

Background: "is deprecated and will be removed" — deprecation warnings for old API names, keywords, and options, and how to migrate before the removal release — this error's family across 29 libraries.

Related errors

AI-assisted analysis of Shopify/liquid@807d45a6b3 (2026-09-08). Data as JSON: /api/errors/b757f95e6ccfb5c2. Report an issue: GitHub.

Appendix: source

Thrown at lib/liquid/template.rb:39

    attr_reader :profiler

    class << self
      # Sets how strict the parser should be.
      # :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 enforces correct syntax for most tags
      # :strict2 enforces correct syntax for all tags
      def error_mode=(mode)
        Deprecations.warn("Template.error_mode=", "Environment#error_mode=")
        Environment.default.error_mode = mode
      end

      def error_mode
        Environment.default.error_mode
      end

      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

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