Hi all! Recently I’ve noticed an issues with autoloading of a specific classes in my app. I’ve created a small project which reproduces the issue: https://github.com/knovoselic/autoload_repro/
All changes required for this repro are part of this commit: https://github.com/knovoselic/autoload_repro/commit/a8cecda742d6d41876abd94f6e0aef4c9758c588
You can just pull the code and run it. The following URL: http://localhost:3000/api/graph/results/crash should crash with uninitialized constant Api::Graph::ResultsController::Graph error.
Calling http://localhost:3000/api/graph/results/success will work fine, and any calls to crash URL after calling success will work fine, until results_controller.rb is modified. Then again crash URL fails.
I’ve been looking into this and I understand that Rails doesn’t know nesting at the point where unknown constant is referenced. This is because Ruby doesn’t provide that info in const_missing method. I’ve been looking at Rails code (specifically lib/active_support/dependencies.rb#load_missing_constant):
def load_missing_constant(from_mod, const_name)
unless qualified_const_defined?(from_mod.name) && Inflector.constantize(from_mod.name).equal?(from_mod)
raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
end
qualified_name = qualified_name_for from_mod, const_name
path_suffix = qualified_name.underscore
file_path = search_for_file(path_suffix)
if file_path
expanded = File.expand_path(file_path)
expanded.sub!(/\.rb\z/, "".freeze)
if loading.include?(expanded)
raise "Circular dependency detected while autoloading constant #{qualified_name}"
else
require_or_load(expanded, qualified_name)
raise LoadError, "Unable to autoload constant #{qualified_name}, expected #{file_path} to define it" unless from_mod.const_defined?(const_name, false)
return from_mod.const_get(const_name)
end
elsif mod = autoload_module!(from_mod, const_name, qualified_name, path_suffix)
return mod
elsif (parent = from_mod.parent) && parent != from_mod &&
! from_mod.parents.any? { |p| p.const_defined?(const_name, false) }
# If our parents do not have a constant named +const_name+ then we are free
# to attempt to load upwards. If they do have such a constant, then this
# const_missing must be due to from_mod::const_name, which should not
# return constants from from_mod's parents.
begin
# Since Ruby does not pass the nesting at the point the unknown
# constant triggered the callback we cannot fully emulate constant
# name lookup and need to make a trade-off: we are going to assume
# that the nesting in the body of Foo::Bar is [Foo::Bar, Foo] even
# though it might not be. Counterexamples are
