add Scanner.Contains (#75)

parser/scanner.go

@@ -73,6 +73,15 @@ var (
 	DefaultLimit = 1
 )
 
+func (s Scanner) Contains(sn Scanner) bool {
+	if s.Filename() != sn.Filename() || s.src != sn.src {
+		return false
+	}
+
+	return s.sliceStart <= sn.sliceStart &&
+		s.sliceStart+s.sliceLength >= sn.sliceStart+sn.sliceLength
+}
+
 func (s Scanner) Context(limitLines int) string {
 	end := s.sliceStart + s.sliceLength
 	lineno, colno := s.Position()

parser/scanner_test.go

@@ -53,6 +53,52 @@ func TestScannerMerge(t *testing.T) {
 	assertMergedScannerErr(t, errors.New("scanners' sources are not the same: {one\ntwo\nthree\nfour } vs {another src }"), []Scanner{*NewScanner(str), *NewScanner("another src")})
 }
 
+func TestContains(t *testing.T) {
+	t.Parallel()
+
+	// in the middle
+	s1 := NewScannerAt("this is a random sentence", 5, 3)
+	s2 := NewScannerAt("this is a random sentence", 6, 1)
+	assert.True(t, s1.Contains(*s2))
+
+	// same range
+	s2.sliceStart = 5
+	s2.sliceLength = 3
+	assert.True(t, s1.Contains(*s2))
+
+	// start same, smaller length
+	s2.sliceLength = 2
+	assert.True(t, s1.Contains(*s2))
+
+	// start in the middle, end at the same part
+	s2.sliceStart = 6
+	assert.True(t, s1.Contains(*s2))
+
+	// start earlier
+	s2.sliceStart = 4
+	assert.False(t, s1.Contains(*s2))
+
+	// start in the middle, end outside
+	s2.sliceStart = 6
+	s2.sliceLength = 5
+	assert.False(t, s1.Contains(*s2))
+
+	// start and end outside range
+	s2.sliceStart = 4
+	s2.sliceLength = 5
+	assert.False(t, s1.Contains(*s2))
+
+	// different filename
+	s1 = NewScannerWithFilename("file1", "file1.wbnf")
+	s2 = NewScannerWithFilename("file2", "file2.wbnf")
+	assert.False(t, s1.Contains(*s2))
+
+	// different source
+	s1 = NewScanner("source1")
+	s2 = NewScanner("source2")
+	assert.False(t, s1.Contains(*s2))
+}
+
 func assertMergedScanner(t *testing.T, src source, offset, length int, items []Scanner) {
 	s, err := MergeScanners(items...)
 	assert.NoError(t, err)