1 files changed, 115 insertions, 0 deletions
diff --git a/plumbing/object/commit_walker_file.go b/plumbing/object/commit_walker_file.go
new file mode 100644
index 0000000..84e738a
--- /dev/null
+++ b/plumbing/object/commit_walker_file.go
@@ -0,0 +1,115 @@
+package object
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+	"io"
+)
+
+type commitFileIter struct {
+	fileName      string
+	sourceIter    CommitIter
+	currentCommit *Commit
+}
+
+// NewCommitFileIterFromIter returns a commit iterator which performs diffTree between
+// successive trees returned from the commit iterator from the argument. The purpose of this is
+// to find the commits that explain how the files that match the path came to be.
+func NewCommitFileIterFromIter(fileName string, commitIter CommitIter) CommitIter {
+	iterator := new(commitFileIter)
+	iterator.sourceIter = commitIter
+	iterator.fileName = fileName
+	return iterator
+}
+
+func (c *commitFileIter) Next() (*Commit, error) {
+	if c.currentCommit == nil {
+		var err error
+		c.currentCommit, err = c.sourceIter.Next()
+		if err != nil {
+			return nil, err
+		}
+	}
+	commit, commitErr := c.getNextFileCommit()
+
+	// Setting current-commit to nil to prevent unwanted states when errors are raised
+	if commitErr != nil {
+		c.currentCommit = nil
+	}
+	return commit, commitErr
+}
+
+func (c *commitFileIter) getNextFileCommit() (*Commit, error) {
+	for {
+		// Parent-commit can be nil if the current-commit is the initial commit
+		parentCommit, parentCommitErr := c.sourceIter.Next()
+		if parentCommitErr != nil {
+			// If the parent-commit is beyond the initial commit, keep it nil
+			if parentCommitErr != io.EOF {
+				return nil, parentCommitErr
+			}
+			parentCommit = nil
+		}
+
+		// Fetch the trees of the current and parent commits
+		currentTree, currTreeErr := c.currentCommit.Tree()
+		if currTreeErr != nil {
+			return nil, currTreeErr
+		}
+
+		var parentTree *Tree
+		if parentCommit != nil {
+			var parentTreeErr error
+			parentTree, parentTreeErr = parentCommit.Tree()
+			if parentTreeErr != nil {
+				return nil, parentTreeErr
+			}
+		}
+
+		// Find diff between current and parent trees
+		changes, diffErr := DiffTree(currentTree, parentTree)
+		if diffErr != nil {
+			return nil, diffErr
+		}
+
+		foundChangeForFile := false
+		for _, change := range changes {
+			if change.name() == c.fileName {
+				foundChangeForFile = true
+				break
+			}
+		}
+
+		// Storing the current-commit in-case a change is found, and
+		// Updating the current-commit for the next-iteration
+		prevCommit := c.currentCommit
+		c.currentCommit = parentCommit
+
+		if foundChangeForFile == true {
+			return prevCommit, nil
+		}
+
+		// If not matches found and if parent-commit is beyond the initial commit, then return with EOF
+		if parentCommit == nil {
+			return nil, io.EOF
+		}
+	}
+}
+
+func (c *commitFileIter) ForEach(cb func(*Commit) error) error {
+	for {
+		commit, nextErr := c.Next()
+		if nextErr != nil {
+			return nextErr
+		}
+		err := cb(commit)
+		if err == storer.ErrStop {
+			return nil
+		} else if err != nil {
+			return err
+		}
+	}
+}
+
+func (c *commitFileIter) Close() {
+	c.sourceIter.Close()
+}