What causes "cannot pass both a module_name and a block" in instructure/canvas-lms?

Remove the block and keep module_name if the extension lives in an existing module

instructure/canvas-lms · error · ArgumentError

cannot pass both a module_name and a block

Error message

cannot pass both a module_name and a block

What it means

Autoextend.hook is strictly either/or: you may supply a module_name (existing module to mix in) OR a &block (inline module), never both. Supplying both is ambiguous — the gem would not know which extension source to use — so hook raises ArgumentError up front.

Solutions

Remove the block and keep module_name if the extension lives in an existing module
Remove the module_name argument and keep the block for an inline extension
Split into two separate hook calls if both extensions are genuinely needed

Example fix

// before
Autoextend.hook('User', 'UserExtensions', :create) { def extra; end }
// after
Autoextend.hook('User', 'UserExtensions', :create)

Defensive patterns

Strategy: validation

Validate before calling

raise 'pass module_name XOR block' if mod_name && block_given?

Try / catch

begin
  Autoextend.hook(const_name, mod_name, method, &blk)
rescue ArgumentError => e
  Rails.logger.error("ambiguous autoextend hook: #{e.message}")
end

Prevention

Pick one extension style per hook and stick to it
Lint initializer files for hook calls containing both forms
Split mixed registrations into separate hook calls

When it happens

Trigger: Calling Autoextend.hook('Model', 'SomeModule', :method) { ... } — a module_name string plus an attached block in the same call.

Common situations: Merging two hook registrations into one call during a refactor; copy-pasting a block-based hook and leaving the old module_name argument in place; IDE snippets that prefill module_name while the developer also writes a block.

Related errors

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/f75a5aa167a36cb9. Report an issue: GitHub.

Appendix: source

Thrown at gems/autoextend/lib/autoextend.rb:66

    # If User is already defined, it will immediately include
    # the MyUserExtension module into it. It then sets up a hook
    # to automatically include in User if it becomes defined again
    # (like from ActiveSupport reloading).
    #
    # You can make an extension optional, which is for information only,
    # so that if you have a spec that checks if all extensions were used
    # it can ignore optional extensions.
    def hook(const_name,
             module_name = nil,
             method: :include,
             singleton: false,
             after_load: false,
             optional: false,
             before: [],
             after: [],
             &block)
      raise ArgumentError, "block is required if module_name is not passed" if !module_name && !block
      raise ArgumentError, "cannot pass both a module_name and a block" if module_name && block

      extension = Extension.new(const_name,
                                module_name,
                                method,
                                block,
                                singleton,
                                optional,
                                Array(before),
                                Array(after))

      const_extensions = extensions_hash[const_name.to_sym] ||= []
      const_extensions << extension

      if module_name.is_a?(Module)
        module_name = module_name.name
      end

      # immediately extend the class if it's already defined

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