Provide config option for shared context metadata behavior.

Previously, it always triggered auto-inclusion based on
matching metadata. The option allows you to opt-in to having
it add the metadata to included groups and examples instead.

- Closes #1790 (this is the last thing necessary for it).
- Addresses #1762.
- Addresses user confusion reported in:
  - rspec/rspec-rails#1241
  - rspec/rspec-rails#1579

Author: myronmarston

Changelog.md

@@ -16,6 +16,10 @@ Enhancements:
 * Add new `config.include_context` API for configuring global or
   filtered inclusion of shared contexts in example groups.
   (Myron Marston, #2256)
+* Add new `config.shared_context_metadata_behavior = :apply_to_host_group`
+  option, which causes shared context metadata to be inherited by the
+  metadata hash of all host groups and examples instead of configuring
+  implicit auto-inclusion based on the passed metadata. (Myron Marston, #2256)
 
 Bug Fixes:
 

features/example_groups/shared_context.feature

@@ -7,7 +7,17 @@ Feature: shared context
   Background:
     Given a file named "shared_stuff.rb" with:
       """ruby
-      RSpec.shared_context "shared stuff" do
+      RSpec.configure do |rspec|
+        # This config option will be enabled by default on RSpec 4,
+        # but for reasons of backwards compatibility, you have to
+        # set it on RSpec 3.
+        #
+        # It causes the host group and examples to inherit metadata
+        # from the shared context.
+        rspec.shared_context_metadata_behavior = :apply_to_host_group
+      end
+
+      RSpec.shared_context "shared stuff", :shared_context => :metadata do
         before { @some_var = :some_value }
         def shared_method
           "it works"
@@ -46,6 +56,13 @@ Feature: shared context
         it "accesses the subject defined in the shared context" do
           expect(subject).to eq('this is the subject')
         end
+
+        group = self
+
+        it "inherits metadata from the included context" do |ex|
+          expect(group.metadata).to include(:shared_context => :metadata)
+          expect(ex.metadata).to include(:shared_context => :metadata)
+        end
       end
       """
     When I run `rspec shared_context_example.rb`
@@ -90,6 +107,13 @@ Feature: shared context
         it "accesses the subject defined in the shared context" do
           expect(subject).to eq('this is the subject')
         end
+
+        group = self
+
+        it "inherits metadata from the included context" do |ex|
+          expect(group.metadata).to include(:shared_context => :metadata)
+          expect(ex.metadata).to include(:shared_context => :metadata)
+        end
       end
       """
     When I run `rspec shared_context_example.rb`
@@ -108,6 +132,10 @@ Feature: shared context
         it "has access to shared methods from examples with matching metadata", :include_shared => true do
           expect(shared_method).to eq("it works")
         end
+
+        it "inherits metadata form the included context due to the matching metadata", :include_shared => true do |ex|
+          expect(ex.metadata).to include(:shared_context => :metadata)
+        end
       end
       """
     When I run `rspec shared_context_example.rb`

lib/rspec/core/configuration.rb

@@ -327,6 +327,59 @@ def treat_symbols_as_metadata_keys_with_true_values=(_value)
         )
       end
 
+      # @macro define_reader
+      # Configures how RSpec treats metadata passed as part of a shared example
+      # group definition. For example, given this shared example group definition:
+      #
+      #     RSpec.shared_context "uses DB", :db => true do
+      #       around(:example) do |ex|
+      #         MyORM.transaction(:rollback => true, &ex)
+      #       end
+      #     end
+      #
+      # ...there are two ways RSpec can treat the `:db => true` metadata, each
+      # of which has a corresponding config option:
+      #
+      # 1. `:trigger_inclusion`: this shared context will be implicitly included
+      #    in any groups (or examples) that have `:db => true` metadata.
+      # 2. `:apply_to_host_group`: the metadata will be inherited by the metadata
+      #    hash of all host groups and examples.
+      #
+      # `:trigger_inclusion` is the legacy behavior from before RSpec 3.5 but should
+      # be considered deprecated. Instead, you can explicitly include a group with
+      # `include_context`:
+      #
+      #     RSpec.describe "My model" do
+      #       include_context "uses DB"
+      #     end
+      #
+      # ...or you can configure RSpec to include the context based on matching metadata
+      # using an API that mirrors configured module inclusion:
+      #
+      #     RSpec.configure do |rspec|
+      #       rspec.include_context "uses DB", :db => true
+      #     end
+      #
+      # `:apply_to_host_group` is a new feature of RSpec 3.5 and will be the only
+      # supported behavior in RSpec 4.
+      #
+      # @overload shared_context_metadata_behavior
+      #   @return [:trigger_inclusion, :apply_to_host_group] the configured behavior
+      # @overload shared_context_metadata_behavior=(value)
+      #   @param value [:trigger_inclusion, :apply_to_host_group] sets the configured behavior
+      define_reader :shared_context_metadata_behavior
+      # @see shared_context_metadata_behavior
+      def shared_context_metadata_behavior=(value)
+        case value
+        when :trigger_inclusion, :apply_to_host_group
+          @shared_context_metadata_behavior = value
+        else
+          raise ArgumentError, "Cannot set `RSpec.configuration." \
+            "shared_context_metadata_behavior` to `#{value.inspect}`. Only " \
+            "`:trigger_inclusion` and `:apply_to_host_group` are valid values."
+        end
+      end
+
       # Record the start time of the spec suite to measure load time.
       add_setting :start_time
 
@@ -398,6 +451,7 @@ def initialize
         @threadsafe = true
         @max_displayed_failure_line_count = 10
         @world = World::Null
+        @shared_context_metadata_behavior = :trigger_inclusion
 
         define_built_in_hooks
       end

lib/rspec/core/shared_example_group.rb

@@ -8,9 +8,10 @@ class SharedExampleGroupModule < Module
       # @private
       attr_reader :definition
 
-      def initialize(description, definition)
+      def initialize(description, definition, metadata)
         @description = description
         @definition  = definition
+        @metadata    = metadata
       end
 
       # Provides a human-readable representation of this module.
@@ -29,6 +30,10 @@ def included(klass)
 
       # @private
       def include_in(klass, inclusion_line, args, customization_block)
+        unless @metadata.empty?
+          klass.update_inherited_metadata(@metadata)
+        end
+
         SharedExampleGroupInclusionStackFrame.with_frame(@description, inclusion_line) do
           klass.class_exec(*args, &@definition)
           klass.class_exec(&customization_block) if customization_block
@@ -150,18 +155,21 @@ def self.remove_globally!
       # @private
       class Registry
         def add(context, name, *metadata_args, &block)
-          ensure_block_has_source_location(block) { CallerFilter.first_non_rspec_line }
-          shared_module = SharedExampleGroupModule.new(name, block)
+          if RSpec.configuration.shared_context_metadata_behavior == :trigger_inclusion
+            return legacy_add(context, name, *metadata_args, &block)
+          end
 
-          if valid_name?(name)
-            warn_if_key_taken context, name, block
-            shared_example_groups[context][name] = shared_module
-          else
-            metadata_args.unshift name
+          unless valid_name?(name)
+            raise ArgumentError, "Shared example group names can only be a string, " \
+                                 "symbol or module but got: #{name.inspect}"
           end
 
-          return if metadata_args.empty?
-          RSpec.configuration.include shared_module, *metadata_args
+          ensure_block_has_source_location(block) { CallerFilter.first_non_rspec_line }
+          warn_if_key_taken context, name, block
+
+          metadata = Metadata.build_hash_from(metadata_args)
+          shared_module = SharedExampleGroupModule.new(name, block, metadata)
+          shared_example_groups[context][name] = shared_module
         end
 
         def find(lookup_contexts, name)
@@ -175,6 +183,25 @@ def find(lookup_contexts, name)
 
       private
 
+        # TODO: remove this in RSpec 4. This exists only to support
+        # `config.shared_context_metadata_behavior == :trigger_inclusion`,
+        # the legacy behavior of shared context metadata, which we do
+        # not want to support in RSpec 4.
+        def legacy_add(context, name, *metadata_args, &block)
+          ensure_block_has_source_location(block) { CallerFilter.first_non_rspec_line }
+          shared_module = SharedExampleGroupModule.new(name, block, {})
+
+          if valid_name?(name)
+            warn_if_key_taken context, name, block
+            shared_example_groups[context][name] = shared_module
+          else
+            metadata_args.unshift name
+          end
+
+          return if metadata_args.empty?
+          RSpec.configuration.include shared_module, *metadata_args
+        end
+
         def shared_example_groups
           @shared_example_groups ||= Hash.new { |hash, context| hash[context] = {} }
         end

spec/rspec/core/configuration_spec.rb

@@ -2414,6 +2414,31 @@ def emulate_not_configured_expectation_framework
       end
     end
 
+    describe "#shared_context_metadata_behavior" do
+      it "defaults to :trigger_inclusion for backwards compatibility" do
+        expect(config.shared_context_metadata_behavior).to eq :trigger_inclusion
+      end
+
+      it "can be set to :apply_to_host_group" do
+        config.shared_context_metadata_behavior = :apply_to_host_group
+        expect(config.shared_context_metadata_behavior).to eq :apply_to_host_group
+      end
+
+      it "can be set to :trigger_inclusion explicitly" do
+        config.shared_context_metadata_behavior = :trigger_inclusion
+        expect(config.shared_context_metadata_behavior).to eq :trigger_inclusion
+      end
+
+      it "cannot be set to any other values" do
+        expect {
+          config.shared_context_metadata_behavior = :another_value
+        }.to raise_error(ArgumentError, a_string_including(
+          "shared_context_metadata_behavior",
+          ":another_value", ":trigger_inclusion", ":apply_to_host_group"
+        ))
+      end
+    end
+
     # assigns files_or_directories_to_run and triggers post-processing
     # via `files_to_run`.
     def assign_files_or_directories_to_run(*value)