Lazy-load profiles + autodiscover plugin gems

Previously every bundled profile (rails, test_frameworks, root_filter,
bundler_filter, hidden_filter) was eagerly required from defaults.rb,
even when the user only needed one of them. Move to lazy loading via
Profiles#fetch_proc, which on a miss tries:

  1. require "simplecov/profiles/<name>"   — bundled profiles
  2. require "simplecov-profile-<name>"    — third-party plugin gems

This both shrinks the default load (rails / test_frameworks no longer
get required unless used) and gives third-party profiles a published
gem-naming convention so users can `SimpleCov.start "myprofile"`
without a manual require beforehand.

Update defaults_spec to use the new public Profiles#fetch_proc rather
than poking the underlying hash directly.

Author: sferik

lib/simplecov/defaults.rb

@@ -2,13 +2,10 @@
 
 require "pathname"
 require_relative "formatter/html_formatter"
-require_relative "profiles/root_filter"
-require_relative "profiles/test_frameworks"
-require_relative "profiles/bundler_filter"
-require_relative "profiles/hidden_filter"
-require_relative "profiles/rails"
 
-# Default configuration
+# Default configuration. Profiles autoload on first reference via
+# `SimpleCov.profiles.fetch_proc`; the unused ones (e.g. "rails",
+# "test_frameworks") never get required unless a user opts in.
 SimpleCov.configure do
   formatter SimpleCov::Formatter::HTMLFormatter
 

lib/simplecov/profiles.rb

@@ -26,10 +26,37 @@ def define(name, &blk)
     # Applies the profile of given name on SimpleCov.configure
     #
     def load(name)
+      SimpleCov.configure(&fetch_proc(name))
+    end
+
+    #
+    # Returns the proc registered for the given profile name, autoloading
+    # bundled or plugin-gem profiles on first lookup. Raises if the profile
+    # cannot be located.
+    #
+    # Lookup order:
+    #   1. already registered via #define
+    #   2. require "simplecov/profiles/<name>"   (bundled profiles)
+    #   3. require "simplecov-profile-<name>"    (third-party plugin gems)
+    #
+    def fetch_proc(name)
       name = name.to_sym
+      autoload_profile(name) unless key?(name)
       raise "Could not find SimpleCov Profile called '#{name}'" unless key?(name)
 
-      SimpleCov.configure(&self[name])
+      self[name]
+    end
+
+  private
+
+    def autoload_profile(name)
+      require "simplecov/profiles/#{name}"
+    rescue LoadError
+      begin
+        require "simplecov-profile-#{name}"
+      rescue LoadError
+        # fall through; #fetch_proc raises the user-facing error
+      end
     end
   end
 end

spec/defaults_spec.rb

@@ -11,7 +11,7 @@
         include SimpleCov::Configuration
 
         def load_profile(name)
-          configure(&SimpleCov.profiles[name.to_sym])
+          configure(&SimpleCov.profiles.fetch_proc(name))
         end
       end
     end