Fix bugs found in fuzzing

parser/fcode_block.go

@@ -78,9 +78,9 @@ func (b *fencedCodeBlockParser) Continue(node ast.Node, reader text.Reader, pc C
 			return Close
 		}
 	}
+	pos, padding := util.DedentPositionPadding(line, reader.LineOffset(), segment.Padding, fdata.indent)
 
-	pos, padding := util.DedentPosition(line, fdata.indent)
-	seg := text.NewSegmentPadding(segment.Start+pos-segment.Padding, segment.Stop, padding)
+	seg := text.NewSegmentPadding(segment.Start+pos, segment.Stop, padding)
 	node.Lines().Append(seg)
 	reader.AdvanceAndSetPadding(segment.Stop-segment.Start-pos-1, padding)
 	return Continue | NoChildren

testutil.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"github.com/yuin/goldmark/util"
 	"os"
+	"runtime/debug"
 	"strconv"
 	"strings"
 	testing "testing"
@@ -78,11 +79,31 @@ func DoTestCaseFile(m Markdown, filename string, t *testing.T) {
 
 func DoTestCases(m Markdown, cases []MarkdownTestCase, t *testing.T) {
 	for _, testCase := range cases {
-		var out bytes.Buffer
-		if err := m.Convert([]byte(testCase.Markdown), &out); err != nil {
-			panic(err)
-		}
-		if !bytes.Equal(bytes.TrimSpace(out.Bytes()), bytes.TrimSpace([]byte(testCase.Expected))) {
+		DoTestCase(m, testCase, t)
+	}
+}
+
+func DoTestCase(m Markdown, testCase MarkdownTestCase, t *testing.T) {
+	var ok bool
+	var out bytes.Buffer
+	defer func() {
+		if err := recover(); err != nil {
+			format := `============= case %d ================
+Markdown:
+-----------
+%s
+
+Expected:
+----------
+%s
+
+Actual
+---------
+%v
+%s
+`
+			t.Errorf(format, testCase.No, testCase.Markdown, testCase.Expected, err, debug.Stack())
+		} else if !ok {
 			format := `============= case %d ================
 Markdown:
 -----------
@@ -98,6 +119,10 @@ Actual
 `
 			t.Errorf(format, testCase.No, testCase.Markdown, testCase.Expected, out.Bytes())
 		}
+	}()
 
+	if err := m.Convert([]byte(testCase.Markdown), &out); err != nil {
+		panic(err)
 	}
+	ok = bytes.Equal(bytes.TrimSpace(out.Bytes()), bytes.TrimSpace([]byte(testCase.Expected)))
 }

util/util.go

@@ -87,31 +87,6 @@ func IsBlank(bs []byte) bool {
 	return true
 }
 
-// DedentPosition dedents lines by the given width.
-func DedentPosition(bs []byte, width int) (pos, padding int) {
-	if width == 0 {
-		return
-	}
-	i := 0
-	l := len(bs)
-	w := 0
-	for ; i < l && w < width; i++ {
-		b := bs[i]
-		if b == ' ' {
-			w++
-		} else if b == '\t' {
-			w += 4
-		} else {
-			break
-		}
-	}
-	padding = w - width
-	if padding < 0 {
-		padding = 0
-	}
-	return i, padding
-}
-
 // VisualizeSpaces visualize invisible space characters.
 func VisualizeSpaces(bs []byte) []byte {
 	bs = bytes.Replace(bs, []byte(" "), []byte("[SPACE]"), -1)
@@ -137,6 +112,9 @@ func TabWidth(currentPos int) int {
 // width=2 is in the tab character. In this case, IndentPosition returns
 // (pos=1, padding=2)
 func IndentPosition(bs []byte, currentPos, width int) (pos, padding int) {
+	if width == 0 {
+		return 0, 0
+	}
 	w := 0
 	l := len(bs)
 	i := 0
@@ -160,6 +138,80 @@ func IndentPosition(bs []byte, currentPos, width int) (pos, padding int) {
 	return -1, -1
 }
 
+// IndentPositionPadding searches an indent position with the given width for the given line.
+// This function is mostly same as IndentPosition except this function
+// takes account into additional paddings.
+func IndentPositionPadding(bs []byte, currentPos, paddingv, width int) (pos, padding int) {
+	if width == 0 {
+		return 0, paddingv
+	}
+	w := 0
+	i := 0
+	l := len(bs)
+	for ; i < l; i++ {
+		if bs[i] == '\t' {
+			w += TabWidth(currentPos + w)
+		} else if bs[i] == ' ' {
+			w++
+		} else {
+			break
+		}
+	}
+	if w >= width {
+		return i - paddingv, w - width
+	}
+	return -1, -1
+}
+
+// DedentPosition dedents lines by the given width.
+func DedentPosition(bs []byte, currentPos, width int) (pos, padding int) {
+	if width == 0 {
+		return 0, 0
+	}
+	w := 0
+	l := len(bs)
+	i := 0
+	for ; i < l; i++ {
+		if bs[i] == '\t' {
+			w += TabWidth(currentPos + w)
+		} else if bs[i] == ' ' {
+			w++
+		} else {
+			break
+		}
+	}
+	if w >= width {
+		return i, w - width
+	}
+	return i, 0
+}
+
+// DedentPositionPadding dedents lines by the given width.
+// This function is mostly same as DedentPosition except this function
+// takes account into additional paddings.
+func DedentPositionPadding(bs []byte, currentPos, paddingv, width int) (pos, padding int) {
+	if width == 0 {
+		return 0, paddingv
+	}
+
+	w := 0
+	i := 0
+	l := len(bs)
+	for ; i < l; i++ {
+		if bs[i] == '\t' {
+			w += TabWidth(currentPos + w)
+		} else if bs[i] == ' ' {
+			w++
+		} else {
+			break
+		}
+	}
+	if w >= width {
+		return i - paddingv, w - width
+	}
+	return i - paddingv, 0
+}
+
 // IndentWidth calculate an indent width for the given line.
 func IndentWidth(bs []byte, currentPos int) (width, pos int) {
 	l := len(bs)