[Fix rubocop#365] Fix false positives for `Performance/ArraySemiInfin…

…iteRangeSlice`

Fixes rubocop#365.

This PR fixes false positives for `Performance/ArraySemiInfiniteRangeSlice`
when using `[]` with string literals.
What this can do is accept string literals, as they are already marked as unsafe.

changelog/fix_false_positives_for_performance_array_semi_infinite_range_slice.md

@@ -0,0 +1 @@
+* [#365](https://github.com/rubocop/rubocop-performance/issues/365): Fix false positives for `Performance/ArraySemiInfiniteRangeSlice` when using `[]` with string literals. ([@koic][])

lib/rubocop/cop/performance/array_semi_infinite_range_slice.rb

@@ -39,7 +39,7 @@ class ArraySemiInfiniteRangeSlice < Base
         RESTRICT_ON_SEND = SLICE_METHODS
 
         def_node_matcher :endless_range_slice?, <<~PATTERN
-          (call $_ $%SLICE_METHODS $#endless_range?)
+          (call $!{str dstr xstr} $%SLICE_METHODS $#endless_range?)
         PATTERN
 
         def_node_matcher :endless_range?, <<~PATTERN

spec/rubocop/cop/performance/array_semi_infinite_range_slice_spec.rb

@@ -77,5 +77,23 @@
         array[-2..]
       RUBY
     end
+
+    it 'does not registers an offense when using `[]` with endless range for string literal' do
+      expect_no_offenses(<<~RUBY)
+        'str'[3..]
+      RUBY
+    end
+
+    it 'does not registers an offense when using `[]` with endless range for interpolated string literal' do
+      expect_no_offenses(<<~'RUBY')
+        "string#{interpolation}"[3..]
+      RUBY
+    end
+
+    it 'does not registers an offense when using `[]` with endless range for backquote string literal' do
+      expect_no_offenses(<<~RUBY)
+        `str`[3..]
+      RUBY
+    end
   end
 end