feat: auto rel=noopener on target=_blank links (configurable)

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project are documented here.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.2.0] - 2026-07-01
+
+### Added
+
+- `config.blank_link_rel` (default `"noopener"`): a `rel` is now emitted automatically on
+  `target="_blank"` anchors. Set `nil` to disable; an explicit `rel="…"` still wins.
+
 ## [1.1.1] - 2026-06-16
 
 ### Added

lib/activemail/components/base.rb

@@ -29,7 +29,7 @@ class Base
       abstract!
 
       IGNORED_ON_PASSTHROUGH = T.let(
-        %w[class id href size large no-expander small target up size-sm size-lg style].freeze,
+        %w[class id href size large no-expander small target rel up size-sm size-lg style].freeze,
         T::Array[String]
       )
 
@@ -103,8 +103,20 @@ def combine_attributes(node, extra_classes = nil)
       end
 
       sig { params(node: Nokogiri::XML::Node).returns(String) }
-      def target_attribute(node)
-        node.attributes['target'] ? %( target="#{escape_attr(node.attributes['target'])}") : ''
+      def link_attributes(node)
+        target = node.attributes['target']&.value
+        rel = resolve_rel(node, target)
+        [
+          target ? %( target="#{escape_attr(target)}") : '',
+          rel ? %( rel="#{escape_attr(rel)}") : ''
+        ].join
+      end
+
+      sig { params(node: Nokogiri::XML::Node, target: T.nilable(String)).returns(T.nilable(String)) }
+      def resolve_rel(node, target)
+        rel = node.attributes['rel']&.value
+        rel = nil if rel&.strip&.empty?
+        rel || (ActiveMail.configuration.blank_link_rel if target == '_blank')
       end
 
       # Outlook-safe nested-table structure kept in one place for <button> and <cta>.

lib/activemail/components/button.rb

@@ -28,11 +28,11 @@ def transform(node, inner)
 
       sig { params(node: Nokogiri::XML::Node, inner: String, expand: T::Boolean).returns(String) }
       def anchor(node, inner, expand)
-        target = target_attribute(node)
+        links = link_attributes(node)
         extra = expand ? ' align="center" class="float-center"' : ''
         # Padding on the <a> makes the whole button a clickable target.
         link_style = "display:inline-block;text-decoration:none;#{BUTTON_PADDING}"
-        attrs = %(#{pass_through_attributes(node)}href="#{escape_attr(node.attr('href'))}"#{target}#{extra})
+        attrs = %(#{pass_through_attributes(node)}href="#{escape_attr(node.attr('href'))}"#{links}#{extra})
         %(<a #{attrs}#{style_attribute(node, link_style)}>#{inner}</a>)
       end
     end

lib/activemail/components/cta.rb

@@ -16,7 +16,7 @@ def transform(node, inner)
         raise ArgumentError, '<cta> requires an href attribute' if node.attr('href').to_s.strip.empty?
 
         style = ActiveMail.tokens.button_style(class?(node, 'secondary') ? :secondary : :primary)
-        anchor = %(<a href="#{escape_attr(node.attr('href'))}"#{target_attribute(node)} ) +
+        anchor = %(<a href="#{escape_attr(node.attr('href'))}"#{link_attributes(node)} ) +
                  %(style="#{link_style(style)}">#{inner}</a>)
         bulletproof_button_table(
           outer_classes: combine_classes(node, 'cta'),

lib/activemail/components/menu_item.rb

@@ -12,7 +12,7 @@ class MenuItem < Base
       def transform(node, inner)
         attributes = combine_attributes(node, 'menu-item')
         # No href → a non-link item, not a broken <a href="">; mirrors <button>.
-        content = node.attr('href') ? %(<a href="#{escape_attr(node.attr('href'))}"#{target_attribute(node)}>#{inner}</a>) : inner
+        content = node.attr('href') ? %(<a href="#{escape_attr(node.attr('href'))}"#{link_attributes(node)}>#{inner}</a>) : inner
         th = ::ActiveMail::Core::INTERIM_TH_TAG
         %(<#{th} #{attributes}#{style_attribute(node)}>#{content}</#{th}>)
       end

lib/activemail/configuration.rb

@@ -86,6 +86,13 @@ def self.assert_positive_dimension!(name, value)
     value
   end
 
+  sig { params(name: Symbol, value: T.untyped).returns(Integer) }
+  def self.positive_integer!(name, value)
+    raise TypeError, "#{name} must be an Integer, got #{value.inspect} (#{value.class})" unless value.is_a?(Integer)
+
+    assert_positive_dimension!(name, value)
+  end
+
   class Configuration
     extend T::Sig
 
@@ -113,16 +120,13 @@ def register_inline_interceptor=(value)
     end
 
     sig { returns(Symbol) }
-    attr_reader :template_engine
-
-    sig { returns(Symbol) }
-    attr_reader :on_parse_error
+    attr_reader :template_engine, :on_parse_error
 
     sig { returns(Integer) }
-    attr_reader :column_count
+    attr_reader :column_count, :container_width
 
-    sig { returns(Integer) }
-    attr_reader :container_width
+    sig { returns(T.nilable(String)) }
+    attr_reader :blank_link_rel
 
     # Mutating the returned hash would bypass validate_component!.
     sig { returns(ActiveMail::ComponentMap) }
@@ -146,6 +150,7 @@ def initialize
       @inliner = T.let(:premailer, InlinerSetting)
       @resolved_inliner = T.let(nil, T.nilable(ActiveMail::Inliner::Base))
       @register_inline_interceptor = T.let(true, T::Boolean)
+      @blank_link_rel = T.let('noopener', T.nilable(String))
     end
 
     # Validates eagerly (like sibling setters): a typo fails at boot, not silently mid-delivery.
@@ -180,12 +185,20 @@ def template_engine=(value)
 
     sig { params(value: T.untyped).returns(Integer) }
     def column_count=(value)
-      @column_count = positive_integer!(:column_count, value)
+      @column_count = ActiveMail.positive_integer!(:column_count, value)
     end
 
     sig { params(value: T.untyped).returns(Integer) }
     def container_width=(value)
-      @container_width = positive_integer!(:container_width, value)
+      @container_width = ActiveMail.positive_integer!(:container_width, value)
+    end
+
+    sig { params(value: T.untyped).returns(T.nilable(String)) }
+    def blank_link_rel=(value)
+      raise TypeError, "blank_link_rel must be a String or nil, got #{value.inspect} (#{value.class})" unless value.nil? || value.is_a?(String)
+
+      normalized = value&.strip
+      @blank_link_rel = normalized&.empty? ? nil : normalized
     end
 
     sig { params(value: T.untyped).returns(ActiveMail::ComponentMap) }
@@ -216,14 +229,5 @@ def resolve_inliner(value)
 
       raise ArgumentError, "unknown inliner #{value.inspect}, expected one of #{INLINERS.keys.inspect}, an Inliner::Base subclass, or an instance"
     end
-
-    # Integer-only (no to_int): a Float would otherwise be silently truncated
-    # (12.9 -> 12), contradicting assert_positive_dimension!'s invariant.
-    sig { params(name: Symbol, value: T.untyped).returns(Integer) }
-    def positive_integer!(name, value)
-      raise TypeError, "#{name} must be an Integer, got #{value.inspect} (#{value.class})" unless value.is_a?(Integer)
-
-      ActiveMail.assert_positive_dimension!(name, value)
-    end
   end
 end

lib/activemail/version.rb

@@ -2,5 +2,5 @@
 # frozen_string_literal: true
 
 module ActiveMail
-  VERSION = '1.1.1'
+  VERSION = '1.2.0'
 end

test/components/button_test.rb

@@ -28,6 +28,45 @@ def test_target_blank_is_preserved
     assert_includes output, 'target="_blank"'
   end
 
+  def test_target_blank_injects_default_rel
+    output = render('<button href="#" target="_blank">B</button>')
+
+    assert_includes output, 'rel="noopener"'
+  end
+
+  def test_non_blank_target_gets_no_rel
+    output = render('<button href="#" target="_self">B</button>')
+
+    refute_includes output, 'rel='
+  end
+
+  def test_no_target_gets_no_rel
+    output = render('<button href="#">B</button>')
+
+    refute_includes output, 'rel='
+  end
+
+  def test_explicit_rel_wins_without_duplication
+    output = render('<button href="#" target="_blank" rel="noopener noreferrer">B</button>')
+
+    assert_includes output, 'rel="noopener noreferrer"'
+    assert_equal 1, output.scan('rel="').size
+  end
+
+  def test_empty_rel_falls_back_to_default
+    output = render('<button href="#" target="_blank" rel="">B</button>')
+
+    assert_includes output, 'rel="noopener"'
+    assert_equal 1, output.scan('rel="').size
+  end
+
+  def test_rel_is_escaped
+    output = render('<button href="#" target="_blank" rel="a&quot;b">B</button>')
+    anchor = Nokogiri::HTML.fragment(output).at_css('a')
+
+    assert_equal 'a"b', anchor['rel']
+  end
+
   def test_classes_are_merged_with_button
     output = render('<button class="small alert" href="#">B</button>')
 

test/components/cta_test.rb

@@ -80,6 +80,26 @@ def test_cta_is_bulletproof_presentation_tables
     assert_equal tables, output.scan('role="presentation"').size
   end
 
+  def test_cta_blank_injects_default_rel
+    output = render('<cta href="#" target="_blank">Go</cta>')
+
+    assert_includes output, 'target="_blank"'
+    assert_includes output, 'rel="noopener"'
+  end
+
+  def test_cta_non_blank_gets_no_rel
+    output = render('<cta href="#">Go</cta>')
+
+    refute_includes output, 'rel='
+  end
+
+  def test_cta_explicit_rel_wins_without_duplication
+    output = render('<cta href="#" target="_blank" rel="noopener noreferrer">Go</cta>')
+
+    assert_includes output, 'rel="noopener noreferrer"'
+    assert_equal 1, output.scan('rel="').size
+  end
+
   def test_info_box_reads_border_token
     ActiveMail.tokens.color(:border, '#445566')
     output = render('<info-box>note</info-box>')

test/components/menu_test.rb

@@ -22,6 +22,19 @@ def test_item_preserves_target
     assert_includes output, 'target="_blank"'
   end
 
+  def test_item_blank_injects_default_rel
+    output = render('<menu><item href="#" target="_blank">I</item></menu>')
+
+    assert_includes output, 'rel="noopener"'
+  end
+
+  def test_item_explicit_rel_wins_without_duplication
+    output = render('<menu><item href="#" target="_blank" rel="noopener noreferrer">I</item></menu>')
+
+    assert_includes output, 'rel="noopener noreferrer"'
+    assert_equal 1, output.scan('rel="').size
+  end
+
   def test_item_without_href_emits_no_broken_anchor
     output = render('<menu><item>Label</item></menu>')
 

test/configuration_test.rb

@@ -9,9 +9,35 @@ def test_defaults
     assert_equal :erb, config.template_engine
     assert_equal 12, config.column_count
     assert_equal 600, config.container_width
+    assert_equal 'noopener', config.blank_link_rel
     assert_empty config.components
   end
 
+  def test_blank_link_rel_override_reflected_in_output
+    ActiveMail.configuration.blank_link_rel = 'noopener noreferrer'
+
+    assert_includes render('<button href="#" target="_blank">B</button>'), 'rel="noopener noreferrer"'
+  end
+
+  def test_blank_link_rel_nil_disables_injection
+    ActiveMail.configuration.blank_link_rel = nil
+
+    refute_includes render('<button href="#" target="_blank">B</button>'), 'rel='
+  end
+
+  def test_blank_link_rel_rejects_invalid
+    config = ActiveMail::Configuration.new
+
+    assert_raises(TypeError) { config.blank_link_rel = 123 }
+  end
+
+  def test_blank_link_rel_empty_string_disables_injection
+    ActiveMail.configuration.blank_link_rel = '  '
+
+    assert_nil ActiveMail.configuration.blank_link_rel
+    refute_includes render('<button href="#" target="_blank">B</button>'), 'rel='
+  end
+
   def test_template_engine_setter_coerces_to_symbol
     config = ActiveMail::Configuration.new
     config.template_engine = 'slim'
@@ -58,7 +84,9 @@ def test_dimension_setters_reject_floats_instead_of_truncating
     config = ActiveMail::Configuration.new
 
     assert_raises(TypeError) { config.column_count = 12.9 }
+    assert_raises(TypeError) { config.container_width = 4.2 }
     assert_equal 12, config.column_count
+    assert_equal 600, config.container_width
   end
 
   def test_constructor_rejects_non_positive_dimensions