fix(status): underlying slice corruption issue

I believe this should fix issues #26 #34 and #35.

commands/status/process.go

@@ -153,9 +153,17 @@ func ProcessChanges(s *bufio.Scanner, root string) ([]*StatusItem, error) {
 		// ...if chunk represents a rename or copy op, need to append another chunk
 		// to get the full change item, with NUL manually reinserted because scanner
 		// will extract past it.
-		if (chunk[0] == 'R' || chunk[0] == 'C') && s.Scan() {
-			chunk = append(chunk, '\x00')
-			chunk = append(chunk, s.Bytes()...)
+		//
+		// Note that the underlying slice from previous scanner.Bytes() MAY be
+		// overridden by subsequent scans, so need to copy it to a new slice
+		// first before scanning to get the next token.
+		if chunk[0] == 'R' || chunk[0] == 'C' {
+			composite := make([]byte, len(chunk))
+			copy(composite, chunk)
+			s.Scan()
+			composite = append(composite, '\x00')
+			composite = append(composite, s.Bytes()...)
+			chunk = composite
 		}
 		statuses, err := processChange(chunk, wd, root)
 		if err != nil {

commands/status/process_test.go

@@ -277,3 +277,28 @@ func TestExtractBranch(t *testing.T) {
 		})
 	}
 }
+
+/*
+// Test to verify https://github.com/mroth/scmpuff/issues/26.
+//
+// Leaving commented out since unlikely to encounter this exact issue again in
+// future, and I'm not sure about importing the user's datafile into this repo.
+//
+// If needed again, the data file is attached to the issue as `output.txt`.
+
+func TestBrokenProcessChanges(t *testing.T) {
+	dat, err := ioutil.ReadFile("testdata/cjfuller_sample.dat")
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := bufio.NewScanner(bytes.NewReader(dat))
+	s.Split(nulSplitFunc)
+	actual, err := ProcessChanges(s, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(actual) != 270 { // `git status -s | wc -l` in replicated repo
+		t.Errorf("expected %v changes, got %v", 270, len(actual))
+	}
+}
+*/