Commits on Oct 16, 2020

1. Remove unused method

   

   marcandre committed Oct 16, 2020
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2. Avoid calling extend in initialize

   

   marcandre committed Oct 16, 2020
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3. Optimize Cop#restrict_on_send …

   We only use the result to iterate, so an array is better here

   

   marcandre committed Oct 16, 2020
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4. Callback building was the single most time consuming method in all Ru… …

   …boCop, at around 8% of overall processing.
   
   This is because we currently build a new `Commissionner` for every file (could be optimized but not easy as config can change) and a commissioner must know which cops need responding to which node types.
   
   Previous method was thus `O(files * cops * types)` where `types` is the number of node types encountered in a typical file.
   Testing on `files == 200` typical RuboCop files, I calculated `types ~22.5`. Currently `cops == 422`.
   
   This new algorithm is the same `O` but `types` is instead the number of types that a cop responds to (on average). For the cops that we run that is ~1.8.
   
   The optimized cache building is almost 6x faster, for an *overall gain of ~6.6%*
   
   It also has the advantage that adding new callbacks has zero impact on the cache building. Note: I'd like to add `on_after_send` etc (see #8844).
   
   The only downside is that the list of callbacks is (by default) cached per Cop class.
   This means that any Cop that somehow relies on *adding* callbacks it responds to *at runtime* is incompatible.
   
   There's a single cop that does this (see #8881). Solutions include: not doing that (as in the PR), or only modifying the callbacks (in this case it could have been done by adding empty methods `on_send`, etc., even though they would be overriden by the extending modules), or overriding `Cop::Base#callbacks_needed` (although I marked the api as private for now).
   
   How I tested performance:
   ```
   $ stackprof tmp/stackprof.dump --text --method 'RuboCop::Cop::Commissioner#cops_callbacks_for'
     samples:  1039 self (7.5%)  /   1104 total (8.0%)
   
   $ stackprof tmp/stackprof.dump --text --method 'RuboCop::Cop::Commissioner#initialize_callbacks'
     samples:    25 self (0.2%)  /    180 total (1.4%)
   
   ```

   

   marcandre committed Oct 16, 2020
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