all: support include directive inside block code

Example of block code with include directive,

----
...
include::file[]
...
----

3 files changed, 63 insertions, 2 deletions

diff --git a/document_parser.go b/document_parser.go
index ca167e6..8de91cc 100644
--- a/document_parser.go
+++ b/document_parser.go
@@ -552,7 +552,7 @@ func (docp *documentParser) parseBlock(parent *element, term int) {
 			el.kind = docp.kind
 			el.addRole(classNameListingBlock)
 			line = docp.consumeLinesUntil(el, docp.kind, nil)
-			el.raw = applySubstitutions(docp.doc, el.raw)
+			el.raw = preprocessBlockCode(docp.doc, el.raw)
 			parent.addChild(el)
 			el = &element{}
 			continue
@@ -872,7 +872,7 @@ func (docp *documentParser) parseListBlock() (el *element, line []byte) {
 				kind: docp.kind,
 			}
 			docp.consumeLinesUntil(el, docp.kind, nil)
-			el.raw = applySubstitutions(docp.doc, el.raw)
+			el.raw = preprocessBlockCode(docp.doc, el.raw)
 			line = nil
 			break
 		}
diff --git a/parser.go b/parser.go
index 6912890..bf435f8 100644
--- a/parser.go
+++ b/parser.go
@@ -314,6 +314,30 @@ var _attrRef = map[string]string{
 	`zwsp`:           htmlSymbolZeroWidthSpace,
 }
 
+// preprocessBlockCode preprocess the content of block code, like "include::"
+// directive, and return the new content.
+func preprocessBlockCode(doc *Document, content []byte) (newContent []byte) {
+	var bbuf bytes.Buffer
+	var lines = bytes.Split(content, []byte{'\n'})
+	for _, line := range lines {
+		if bytes.HasPrefix(line, []byte(`include::`)) {
+			var elInclude = parseInclude(doc, line)
+			if elInclude != nil {
+				bbuf.Write(elInclude.content)
+				bbuf.WriteByte('\n')
+				continue
+			}
+		}
+		bbuf.Write(line)
+		bbuf.WriteByte('\n')
+	}
+
+	newContent = applySubstitutions(doc, bbuf.Bytes())
+	return newContent
+}
+
+// applySubstitutions scan the content and replace attribute reference "{}"
+// with its value, and character '<', '>', '&' with HTML symbol.
 func applySubstitutions(doc *Document, content []byte) []byte {
 	var (
 		raw    = bytes.TrimRight(content, " \n")
diff --git a/testdata/include_code_block_test.txt b/testdata/include_code_block_test.txt
new file mode 100644
index 0000000..6215062
--- /dev/null
+++ b/testdata/include_code_block_test.txt
@@ -0,0 +1,37 @@
+Test include directive inside source code block.
+
+>>> case-01
+
+----
+include::testdata/_includes/fragment1.adoc[]
+----
+
+<<< case-01
+
+<div class="listingblock">
+<div class="content">
+<pre>// SPDX-FileCopyrightText: 2020 M. Shulhan &lt;ms@kilabit.info&gt;
+// SPDX-License-Identifier: GPL-3.0-or-later
+This is inside the fragment1.adoc.</pre>
+</div>
+</div>
+
+>>> case-02
+
+----
+before
+include::testdata/_includes/fragment1.adoc[]
+after
+----
+
+<<< case-02
+
+<div class="listingblock">
+<div class="content">
+<pre>before
+// SPDX-FileCopyrightText: 2020 M. Shulhan &lt;ms@kilabit.info&gt;
+// SPDX-License-Identifier: GPL-3.0-or-later
+This is inside the fragment1.adoc.
+after</pre>
+</div>
+</div>