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@@ -149,8 +149,24 @@ module Grit
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       commits
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     end
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-    def self.diff(repo, a, b = nil)
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-      text = repo.git.diff({:full_index => true}, a, b)
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+    # Show diffs between two trees:
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+    #   +repo+ is the Repo
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+    #   +a+ is a named commit
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+    #   +b+ is an optional named commit.  Passing an array assumes you 
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+    #     wish to omit the second named commit and limit the diff to the 
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+    #     given paths.
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+    #   +paths* is an array of paths to limit the diff.
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+    #
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+    # Returns Grit::Diff[] (baked)
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+    def self.diff(repo, a, b = nil, paths = [])
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+      if b.is_a?(Array)
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+        paths = b
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+        b     = nil
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+      end
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+      paths.unshift("--") unless paths.empty?
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+      paths.unshift(b)    unless b.nil?
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+      paths.unshift(a)
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+      text = repo.git.diff({:full_index => true}, *paths)
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       Diff.list_from_string(repo, text)
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     end
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@@ -28,7 +28,7 @@ class TestCommit < Test::Unit::TestCase
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   def test_diff
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     # git diff --full-index 91169e1f5fa4de2eaea3f176461f5dc784796769 > test/fixtures/diff_p
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-    Git.any_instance.expects(:diff).returns(fixture('diff_p'))
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+    Git.any_instance.expects(:diff).with({:full_index => true}, 'master').returns(fixture('diff_p'))
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     diffs = Commit.diff(@r, 'master')
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     assert_equal 15, diffs.size
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@@ -47,6 +47,30 @@ class TestCommit < Test::Unit::TestCase
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     assert_equal 'f733bce6b57c0e5e353206e692b0e3105c2527f4', diffs[5].b_commit.id
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     assert_equal true, diffs[5].new_file
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   end
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+  
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+  def test_diff_with_two_commits
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+    # git diff --full-index 59ddc32 13d27d5 > test/fixtures/diff_2
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+    Git.any_instance.expects(:diff).with({:full_index => true}, '59ddc32', '13d27d5').returns(fixture('diff_2'))
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+    diffs = Commit.diff(@r, '59ddc32', '13d27d5')
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+    
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+    assert_equal 3, diffs.size
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+  end
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+  
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+  def test_diff_with_files
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+    # git diff --full-index 59ddc32 -- lib > test/fixtures/diff_f
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+    Git.any_instance.expects(:diff).with({:full_index => true}, '59ddc32', '--', 'lib').returns(fixture('diff_f'))
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+    diffs = Commit.diff(@r, '59ddc32', %w(lib))
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+    
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+    assert_equal 1, diffs.size
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+  end
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+  
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+  def test_diff_with_two_commits_and_files
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+    # git diff --full-index 59ddc32 13d27d5 -- lib > test/fixtures/diff_2f
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+    Git.any_instance.expects(:diff).with({:full_index => true}, '59ddc32', '13d27d5', '--', 'lib').returns(fixture('diff_2f'))
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+    diffs = Commit.diff(@r, '59ddc32', '13d27d5', %w(lib))
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+    
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+    assert_equal 1, diffs.size
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+  end
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   # diffs
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   def test_diffs