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Fix a false negative for Performance/ChainArrayAllocation #294

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Jun 16, 2022
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Fix a false negative for Performance/ChainArrayAllocation #294

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1 change: 1 addition & 0 deletions changelog/fix_false_negative_for_performance_chain_array_allocation.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
* [#294](https://github.com/rubocop/rubocop-performance/pull/294): Fix a false negative for `Performance/ChainArrayAllocation` when using `array.first(do_something).uniq`. ([@koic][])
2 changes: 1 addition & 1 deletion lib/rubocop/cop/performance/chain_array_allocation.rb
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Expand Up @@ -53,7 +53,7 @@ class ChainArrayAllocation < Base

def_node_matcher :chain_array_allocation?, <<~PATTERN
(send {
(send _ $%RETURN_NEW_ARRAY_WHEN_ARGS {int lvar ivar cvar gvar})
(send _ $%RETURN_NEW_ARRAY_WHEN_ARGS {int lvar ivar cvar gvar send})
(block (send _ $%ALWAYS_RETURNS_NEW_ARRAY) ...)
(send _ $%RETURNS_NEW_ARRAY ...)
} $%HAS_MUTATION_ALTERNATIVE ...)
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7 changes: 7 additions & 0 deletions spec/rubocop/cop/performance/chain_array_allocation_spec.rb
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Expand Up @@ -23,6 +23,13 @@
^^^^^ Use unchained `first` and `uniq!` (followed by `return array` if required) instead of chaining `first...uniq`.
RUBY
end

it 'registers an offense for `first(do_something).uniq`' do
expect_offense(<<~RUBY)
[1, 2, 3, 4].first(do_something).uniq
^^^^^ Use unchained `first` and `uniq!` (followed by `return array` if required) instead of chaining `first...uniq`.
RUBY
end
end

describe 'methods that only return an array with no block' do
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