Performance/Sum not autocorrecting injects or reduces with blocks

[jmkoni]

Expected behavior

After enabling Performance/Sum, I expect that the following lines will all be autocorrected to use sum:

[1, 2, 3].inject(:+)
[1, 2, 3].reduce(10, :+)
[1, 2, 3].reduce { |acc, elem| acc + elem }

Actual behavior

It only autocorrects the second line:

[1, 2, 3].inject(:+)
[1, 2, 3].sum(10)
[1, 2, 3].reduce { |acc, elem| acc + elem }

Steps to reproduce the problem

1. Create a test file with those lines.
2. Run rubocop -A
   OR
   You can replicate this bug by pulling down this project, doing a bundle install, and running rubocop -A

RuboCop version

rubocop -V
0.91.0 (using Parser 2.7.1.4, rubocop-ast 0.4.2, running on ruby 2.7.0 x86_64-darwin19)

[jmkoni]

[1,2,3].reduce(:+) also doesn't autocorrect

[fatkodima]

This is an expected behavior, example - https://github.com/rubocop-hq/rubocop-performance/blob/368b748d1c6df62002f2a1b58e4258100e693841/spec/rubocop/cop/performance/sum_spec.rb#L73-L80

We cannot autocorrect when initial value is not given, because we do not know array item types.
For example, if we try to autocorrect arr.inject(:+) to arr.sum, where arr = ['foo', 'bar'], then this will produce an error, because it should be autocorrected to arr.sum('').

[fatkodima]

Or we can autocorrect, but mark this cop as unsafe.

[jmkoni]

Somehow I was not notified on these updates. Thank you for the clarification.