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Fix keyword arguments in dynamic method dispatch #2509

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Fix keyword arguments in dynamic method dispatch #2509

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ec244b0
Fix keyword arguments in dynamic matchers
JoshCheek Jul 15, 2021
e4b3953
Update controller_example_group_spec.rb
pirj Jul 15, 2021
e2541f0
Update spec/rspec/rails/example/controller_example_group_spec.rb
pirj Jul 27, 2021
cb7e2d4
Update spec/rspec/rails/example/controller_example_group_spec.rb
pirj Jul 27, 2021
0b74226
Revert the previous spec change
pirj Jul 27, 2021
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1 change: 1 addition & 0 deletions lib/rspec/rails/example/controller_example_group.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,7 @@ def method_missing(method, *args, &block)
super
end
end
ruby2_keywords :method_missing if respond_to?(:ruby2_keywords, true)

included do
subject { controller }
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7 changes: 7 additions & 0 deletions spec/rspec/rails/example/controller_example_group_spec.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,13 @@ def group_for(klass)
expect(group.included_modules).to include(RSpec::Rails::Matchers::RoutingMatchers)
end

it "handles methods invoked via `method_missing` that use keywords" do
example = group.new
example.define_singleton_method(:has_val?) { |val:| val == 1 }
expect(example).to example.have_val(val: 1)
expect(example).to_not example.have_val(val: 2)
Comment on lines +24 to +26
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Suggested change
example.define_singleton_method(:has_val?) { |val:| val == 1 }
expect(example).to example.have_val(val: 1)
expect(example).to_not example.have_val(val: 2)
example.define_singleton_method(:keyword_value) { |value:| value }
expect(example.keyword_value(value: 42)).to eq 42

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I'd prefer a clear example method here not something imitating a matcher as thats not what is the issue.

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This test is not hitting the method_missing. We defined keyword_value and call it.

The current expect(example).to example.have_val(val: 1) works, but it's incredibly confusing.

expect { example.have_val(val: 1) }.not_to raise_error

failed to catch the regression, it doesn't fail if ruby2_keywords is removed.

I'll figure out a self-explanatory spec to cover this. I intend to rely on dynamic matchers, but will try to avoid the expect(example).to part.

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I just don't want a have_ anything style example, its confusing, its the method dispatch thats the bug here, not matchers.

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It's a bit of both.

To reproduce the issue:

  • it is not sufficient for us to just call the same method that we define, as method_missing won't be called
  • there should be some code that handles method_missing below ControllerExampleGroup and below Rails
  • this code should accept arguments and pass it to a method that accepts keyword arguments

We could write a spec with something like prepend Module.new { def method_missing ... }, but this might be excessively complicated.

There are dynamic matchers. They do exactly what we want - they have a method_missing, and they can delegate to the method we define.

It's still a brain-teaser how to express the case in a spec. The best I could think of so far:

expect {
  example.have_val(val: 1).matches?(example)
}.not_to raise_error

example.have_val goes through ControllerExampleGroup's method_missing, then through Rails' one, and lands in dynamic matchers. They save the kwarg to @args, and the flag that it's a kwarg is already set on the object.
matches? calls has_val? on the example, and passes *@args to it.

It's not necessary to call have_val on example, and we could:

expect(example).to have_val(val: 1)

but in this case ControllerExampleGroup's method_missing is never called, and it's dynamic matchers' method_missing who sets the flag. I.e. this fix would not be covered by such a test.

Frankly speaking, it seems like it doesn't matter much what exactly the spec will be, we'll have to add a chunk of code comments along. And I have strong doubts that in a month from now it will take me less than half an hour to recall all the details about this tangled case.

I'm out of good ideas.

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If my change doesn't trigger method missing neither does the original, they both call the method directly I just skip the expect to. So my original point stands here, please construct an example that doesn't look like a matcher.

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@JonRowe There is a significant difference. You call a method that we've just defined, keyword_value, while the original example calls a non-existent method, have_val, while we define has_val?.

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Ah tired eyes etc, ok fine, implement a method missing and remove the has / have names. This is a lot of conversation for a simple fix, but it needs to not be confused with matchers. Its method_missing and the method names that are causing this.

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Right. Dynamic matchers are a victim here.
And they are the only known victim. And they apparently are the only way to test the fix without involving in_sub_process { ControllerExampleGroup.prepend Module.new { def method_missing ... end } }.

end

context "with implicit subject" do
it "uses the controller as the subject" do
controller = double('controller')
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