From 353e25c740f5c31d202a67444b3973108e787554 Mon Sep 17 00:00:00 2001
From: Markus Schirp <mbj@schirp-dso.com>
Date: Sun, 12 May 2024 00:16:44 +0000
Subject: [PATCH] Add ordering mutations

[fix #1442]
---
 Changelog.md                     | 12 ++++++++
 lib/mutant/mutation/operators.rb | 10 +++++++
 meta/send.rb                     | 51 ++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+)

diff --git a/Changelog.md b/Changelog.md
index e59c9a057..eb6e4da36 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,5 +1,17 @@
 # v0.12.1 2024-05-11
 
+* [#1444](https://github.com/mbj/mutant/pull/1444)
+
+  Add ordering mutations to full and light operator set,
+  `#find/#detect/#min/#max/#min_by/#max_by -> #first/#last`. These mutations force
+  to provide test cases with more than one element to observe the extra
+  semantics by these methods over just `#first` and `#last`.
+
+  Add `#first -> #last` and `#last -> #first` to full operator set. These where
+  highly controversial in the past and thus where removed. People who do not care
+  about ordering of their collections can now choose the light operator set, so people who care
+  (and should care) can now care (again).
+
 * [#1443](https://github.com/mbj/mutant/pull/1443)
 
   Change mutants test runner to always report in test definition order deterministically.
diff --git a/lib/mutant/mutation/operators.rb b/lib/mutant/mutation/operators.rb
index 770c5e201..49e7c8498 100644
--- a/lib/mutant/mutation/operators.rb
+++ b/lib/mutant/mutation/operators.rb
@@ -21,14 +21,22 @@ class Full < self
           all?:          %i[any?],
           any?:          %i[all?],
           at:            %i[fetch key?],
+          detect:        %i[first last],
           fetch:         %i[key?],
+          find:          %i[first last],
+          first:         %i[last],
           flat_map:      %i[map],
           gsub:          %i[sub],
           is_a?:         %i[instance_of?],
           kind_of?:      %i[instance_of?],
+          last:          %i[first],
           map:           %i[each],
           match:         %i[match?],
+          max:           %i[first last],
+          max_by:        %i[first last],
           method:        %i[public_method],
+          min:           %i[first last],
+          min_by:        %i[first last],
           reverse_each:  %i[each],
           reverse_map:   %i[map each],
           reverse_merge: %i[merge],
@@ -49,6 +57,8 @@ class Light < self
           .tap do |replacements|
             replacements.delete(:==)
             replacements.delete(:eql?)
+            replacements.delete(:first)
+            replacements.delete(:last)
           end
           .freeze
       end
diff --git a/meta/send.rb b/meta/send.rb
index 022e2d526..c6a0ec6c7 100644
--- a/meta/send.rb
+++ b/meta/send.rb
@@ -884,3 +884,54 @@
   mutation 'foo(nil)'
   mutation 'foo(:"+__mutant__")'
 end
+
+Mutant::Meta::Example.add :send, operators: :light do
+  source 'first'
+
+  singleton_mutations
+end
+
+Mutant::Meta::Example.add :send, operators: :light do
+  source 'last'
+
+  singleton_mutations
+end
+
+Mutant::Meta::Example.add :send, operators: :full do
+  source 'first'
+
+  singleton_mutations
+
+  mutation 'last'
+end
+
+Mutant::Meta::Example.add :send, operators: :full do
+  source 'last'
+
+  singleton_mutations
+
+  mutation 'first'
+end
+
+%w[detect find max max_by min min_by].each do |selector|
+  Mutant::Meta::Example.add :send do
+    source selector
+
+    singleton_mutations
+
+    mutation 'first'
+    mutation 'last'
+  end
+
+  Mutant::Meta::Example.add :send do
+    source "#{selector}(&:block)"
+
+    singleton_mutations
+
+    mutation "#{selector}(&:block__mutant__)"
+    mutation "#{selector}(&nil)"
+    mutation 'first(&:block)'
+    mutation 'last(&:block)'
+    mutation selector
+  end
+end