From 907eb998359943d57fc0dd77f83a84f4bb431573 Mon Sep 17 00:00:00 2001
From: yuin <yuin@inforno.net>
Date: Mon, 8 Nov 2021 16:13:54 +0900
Subject: [PATCH] Fixes #262

---
 _test/extra.txt       | 22 ++++++++++++++++++
 parser/fcode_block.go |  3 +++
 util/util.go          | 53 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+)

diff --git a/_test/extra.txt b/_test/extra.txt
index f202b13..748a4ef 100644
--- a/_test/extra.txt
+++ b/_test/extra.txt
@@ -649,3 +649,25 @@ b
 <p>a <br />
 b</p>
 //= = = = = = = = = = = = = = = = = = = = = = = =//
+
+
+51: Empty line in a fenced code block under list items
+//- - - - - - - - -//
+* This is a list item
+    ```
+    This is a test
+
+    This line will be dropped.
+    This line will be displayed.
+    ```
+//- - - - - - - - -//
+<ul>
+<li>This is a list item
+<pre><code>This is a test
+
+This line will be dropped.
+This line will be displayed.
+</code></pre>
+</li>
+</ul>
+//= = = = = = = = = = = = = = = = = = = = = = = =//
diff --git a/parser/fcode_block.go b/parser/fcode_block.go
index 7e44cec..5914138 100644
--- a/parser/fcode_block.go
+++ b/parser/fcode_block.go
@@ -90,6 +90,9 @@ func (b *fencedCodeBlockParser) Continue(node ast.Node, reader text.Reader, pc C
 	pos, padding := util.IndentPositionPadding(line, reader.LineOffset(), segment.Padding, fdata.indent)
 	if pos < 0 {
 		pos = util.FirstNonSpacePosition(line)
+		if pos < 0 {
+			pos = 0
+		}
 		padding = 0
 	}
 	seg := text.NewSegmentPadding(segment.Start+pos, segment.Stop, padding)
diff --git a/util/util.go b/util/util.go
index 4d432d8..a817ec6 100644
--- a/util/util.go
+++ b/util/util.go
@@ -180,6 +180,59 @@ func IndentPositionPadding(bs []byte, currentPos, paddingv, width int) (pos, pad
 	return -1, -1
 }
 
+// DedentPosition dedents lines by the given width.
+//
+// Deprecated: This function has bugs. Use util.IndentPositionPadding and util.FirstNonSpacePosition.
+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.
+//
+// Deprecated: This function has bugs. Use util.IndentPositionPadding and util.FirstNonSpacePosition.
+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)