Add caller_filter from rspec-core.

lib/rspec/caller_filter.rb

@@ -0,0 +1,55 @@
+module RSpec
+  # Consistent implementation for "cleaning" the caller method to strip out
+  # non-rspec lines. This enables errors to be reported at the call site in
+  # the code using the library, which is far more useful than the particular
+  # internal method that raised an error.
+  class CallerFilter
+
+    # This list is an unfortunate dependency on other RSpec core libraries.
+    # It would be nice if this was not needed.
+    RSPEC_LIBS = %w[
+      core
+      mocks
+      expectations
+      matchers
+      rails
+    ]
+
+    LIB_REGEX = %r{/lib/rspec/(#{RSPEC_LIBS.join('|')})(\.rb|/)}
+
+    if RUBY_VERSION >= '2.0.0'
+      def self.first_non_rspec_line
+        # `caller` is an expensive method that scales linearly with the size of
+        # the stack. The performance hit for fetching it in chunks is small,
+        # and since the target line is probably near the top of the stack, the
+        # overall improvement of a chunked search like this is significant.
+        #
+        # See benchmarks/caller.rb for measurements.
+
+        # Initial value here is mostly arbitrary, but is chosen to give good
+        # performance on the common case of creating a double.
+        increment = 5
+        i         = 1
+        line      = nil
+
+        while !line
+          stack = caller(i, increment)
+          raise "No non-lib lines in stack" unless stack
+
+          line = stack.find { |l| l !~ LIB_REGEX }
+
+          i         += increment
+          increment *= 2 # The choice of two here is arbitrary.
+        end
+
+        line
+      end
+    else
+      # Earlier rubies do not support the two argument form of `caller`. This
+      # fallback is logically the same, but slower.
+      def self.first_non_rspec_line
+        caller.find { |line| line !~ LIB_REGEX }
+      end
+    end
+  end
+end

lib/rspec/expectations/deprecation.rb

@@ -1,3 +1,5 @@
+require 'rspec/caller_filter'
+
 module RSpec
   module Expectations
     module Deprecation
@@ -7,7 +9,7 @@ module Deprecation
       def deprecate(deprecated, options={})
         message = "DEPRECATION: #{deprecated} is deprecated."
         message << " Use #{options[:replacement]} instead." if options[:replacement]
-        message << " Called from #{caller(0)[2]}."
+        message << " Called from #{CallerFilter.first_non_rspec_line}."
         warn message
       end
     end

spec/rspec/expectations_spec.rb

@@ -0,0 +1,18 @@
+module RSpec
+  describe Expectations do
+    def file_contents_for(lib, filename)
+      # http://rubular.com/r/HYpUMftlG2
+      path = $LOAD_PATH.find { |p| p.match(/\/rspec-#{lib}(-[a-f0-9]+)?\/lib/) }
+      file = File.join(path, filename)
+      File.read(file)
+    end
+
+    it 'has an up-to-date rspec/caller_filter file' do
+      expectations = file_contents_for("expectations", "rspec/caller_filter.rb")
+      core         = file_contents_for("core",         "rspec/caller_filter.rb")
+
+      expect(expectations).to eq(core)
+    end
+  end
+end
+