From ee2b84f3cbd97d8116467ea0d44b8182824c83ab Mon Sep 17 00:00:00 2001
From: Daniel Lopez Prat <daniel@6temes.cat>
Date: Wed, 21 Nov 2018 08:54:22 +0900
Subject: [PATCH] Add slice! method to ActiveModel::Errors

---
 activemodel/CHANGELOG.md               |  4 ++++
 activemodel/lib/active_model/errors.rb | 11 +++++++++++
 activemodel/test/cases/errors_test.rb  | 24 ++++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 6048911217..0bc8728e36 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `#slice!` method to `ActiveModel::Errors`.
+
+    *Daniel López Prat*
+
 *   Fix numericality validator to still use value before type cast except Active Record.
 
     Fixes #33651, #33686.
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 9de6b609a3..969effdc20 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -112,6 +112,17 @@ def merge!(other)
       @details.merge!(other.details) { |_, ary1, ary2| ary1 + ary2 }
     end
 
+    # Removes all errors except the given keys. Returns a hash containing the removed errors.
+    #
+    #   person.errors.keys                  # => [:name, :age, :gender, :city]
+    #   person.errors.slice!(:age, :gender) # => { :name=>["cannot be nil"], :city=>["cannot be nil"] }
+    #   person.errors.keys                  # => [:age, :gender]
+    def slice!(*keys)
+      keys = keys.map(&:to_sym)
+      @details.slice!(*keys)
+      @messages.slice!(*keys)
+    end
+
     # Clear the error messages.
     #
     #   person.errors.full_messages # => ["name cannot be nil"]
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index 185b5a24ae..f9015b869d 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -411,6 +411,30 @@ def test_no_key
     assert_equal({ name: [{ error: :blank }, { error: :invalid }] }, person.errors.details)
   end
 
+  test "slice! removes all errors except the given keys" do
+    person = Person.new
+    person.errors.add(:name, "cannot be nil")
+    person.errors.add(:age, "cannot be nil")
+    person.errors.add(:gender, "cannot be nil")
+    person.errors.add(:city, "cannot be nil")
+
+    person.errors.slice!(:age, "gender")
+
+    assert_equal [:age, :gender], person.errors.keys
+  end
+
+  test "slice! returns the deleted errors" do
+    person = Person.new
+    person.errors.add(:name, "cannot be nil")
+    person.errors.add(:age, "cannot be nil")
+    person.errors.add(:gender, "cannot be nil")
+    person.errors.add(:city, "cannot be nil")
+
+    removed_errors = person.errors.slice!(:age, "gender")
+
+    assert_equal({ name: ["cannot be nil"], city: ["cannot be nil"] }, removed_errors)
+  end
+
   test "errors are marshalable" do
     errors = ActiveModel::Errors.new(Person.new)
     errors.add(:name, :invalid)
-- 
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