Allow clearing one cached source file

lib/method_source.rb

@@ -55,9 +55,15 @@ def self.lines_for(file_name, name=nil)
     raise SourceNotFoundError, "Could not load source for #{name}: #{e.message}"
   end
 
-  # Clear cache.
-  def self.clear_cache
-    @lines_for_file = {}
+  # Clear cached source lines.
+  #
+  # @param [String, nil] file_name  The file to evict, or nil to clear all files.
+  def self.clear_cache(file_name=nil)
+    if file_name
+      @lines_for_file.delete(file_name) if @lines_for_file
+    else
+      @lines_for_file = {}
+    end
   end
 
   # @deprecated — use MethodSource::CodeHelpers#complete_expression?
@@ -174,4 +180,3 @@ class Proc
   include MethodSource::SourceLocation::ProcExtensions
   include MethodSource::MethodExtensions
 end
-

spec/method_source_spec.rb

@@ -1,7 +1,37 @@
 require 'spec_helper'
+require 'tempfile'
 
 describe MethodSource do
 
+  describe ".clear_cache" do
+    it "can evict one file without clearing other cached files" do
+      first = Tempfile.new("method-source-first")
+      second = Tempfile.new("method-source-second")
+
+      first.write("first old\n")
+      second.write("second old\n")
+      first.flush
+      second.flush
+
+      expect(MethodSource.lines_for(first.path)).to eq(["first old\n"])
+      expect(MethodSource.lines_for(second.path)).to eq(["second old\n"])
+
+      File.write(first.path, "first new\n")
+      File.write(second.path, "second new\n")
+      MethodSource.clear_cache(first.path)
+
+      expect(MethodSource.lines_for(first.path)).to eq(["first new\n"])
+      expect(MethodSource.lines_for(second.path)).to eq(["second old\n"])
+
+      MethodSource.clear_cache
+      expect(MethodSource.lines_for(second.path)).to eq(["second new\n"])
+    ensure
+      MethodSource.clear_cache
+      first.close!
+      second.close!
+    end
+  end
+
   describe "source_location (testing 1.8 implementation)" do
     it 'should return correct source_location for a method' do
       expect(method(:hello).source_location.first).to match(/spec_helper/)