feat: check that non-linear content is reachable

EPUB 3.3 says:
> EPUB creators MUST provide a means of accessing all non-linear content
> (e.g., hyperlinks in the content or from the EPUB navigation document).

This commit adds a check for the above statement.
- new error `OPF-096` is reported when no hyperlink was found to
  non-linear content in an EPUB with no script
- new usage `OPF-096b` is reported when no hyperlink was found to
  non-linear content in a scripted EPUB (a link may be added via
  scripting, so we cannot report this as an error)

Fix #1451

src/main/java/com/adobe/epubcheck/messages/DefaultSeverities.java

@@ -289,6 +289,8 @@ private void initialize()
     severities.put(MessageId.OPF_093, Severity.ERROR);
     severities.put(MessageId.OPF_094, Severity.ERROR);
     severities.put(MessageId.OPF_095, Severity.ERROR);
+    severities.put(MessageId.OPF_096, Severity.ERROR);
+    severities.put(MessageId.OPF_096b, Severity.USAGE);
 
     // PKG
     severities.put(MessageId.PKG_001, Severity.WARNING);

src/main/java/com/adobe/epubcheck/messages/MessageId.java

@@ -283,6 +283,8 @@ public enum MessageId implements Comparable<MessageId>
   OPF_093("OPF-093"),
   OPF_094("OPF-094"),
   OPF_095("OPF-095"),
+  OPF_096("OPF-096"),
+  OPF_096b("OPF-096b"),
 
   // Messages relating to the entire package
   PKG_001("PKG-001"),

src/main/java/com/adobe/epubcheck/opf/OPFChecker30.java

@@ -24,6 +24,7 @@
 
 import java.util.Set;
 
+import org.w3c.epubcheck.core.references.Reference;
 import org.w3c.epubcheck.util.url.URLFragment;
 
 import com.adobe.epubcheck.api.EPUBLocation;
@@ -183,6 +184,26 @@ else if (!overlayTextChecker.isCorrectOverlay(docURL, mo))
         }
       }
     }
+
+    // check that non-linear content documents are reachable
+    if (item.isInSpine() && !item.isLinear() && context.referenceRegistry.isPresent()
+    // search the reference registry for any hyperlink pointing to this item
+        && !context.referenceRegistry.get().asList().stream()
+            .anyMatch(ref -> ref.type == Reference.Type.HYPERLINK
+                && ref.targetResource.equals(item.getURL())))
+    {
+      // if content is scripted, references can be added by scripting
+      // se we only report a usage
+      if (context.featureReport.hasFeature(FeatureEnum.HAS_SCRIPTS))
+      {
+        report.message(MessageId.OPF_096b, item.getLocation(), item.getPath());
+      }
+      // else, report an error if no hyperlink were found
+      else
+      {
+        report.message(MessageId.OPF_096, item.getLocation(), item.getPath());
+      }
+    }
   }
 
   @Override
@@ -194,14 +215,15 @@ protected void checkSpineItem(OPFItem item, OPFHandler opfHandler)
       return;
     }
 
-    String mimeType = item.getMimeType();
-
+    // check properties
     if (item.getProperties()
         .contains(PackageVocabs.ITEM_VOCAB.get(PackageVocabs.ITEM_PROPERTIES.DATA_NAV)))
     {
       report.message(MessageId.OPF_077, item.getLocation());
     }
 
+    // check that spine items have content document fallback
+    String mimeType = item.getMimeType();
     if (!isBlessedItemType(mimeType, version))
     {
       if (!item.hasFallback())
@@ -213,7 +235,6 @@ else if (!item.hasContentDocumentFallback())
         report.message(MessageId.OPF_044, item.getLocation(), mimeType);
       }
     }
-
   }
 
   private void checkCollections()

src/main/resources/com/adobe/epubcheck/messages/MessageBundle.properties

@@ -210,7 +210,9 @@ OPF_091=The item href URL must not have a fragment identifier.
 OPF_092=Language tag "%1$s" is not well-formed: %2$s
 OPF_093=The "media-type" attribute is required for linked resources located in the EPUB container
 OPF_094=The "media-type" attribute is required for "%1$s" links.
-OPF_095=The "media-type" attribute of "voicing" links must be an audio MIME type, but found "%1$s". 
+OPF_095=The "media-type" attribute of "voicing" links must be an audio MIME type, but found "%1$s".
+OPF_096=Non-linear content must be reachable, but found no hyperlink to "%1$s".
+OPF_096b=No hyperlink was found to non-linear document "%1$s", please check that it can be reached from scripted content.  
 
 #Package
 PKG_001=Validating the EPUB against version %1$s but detected version %2$s.

src/test/resources/epub-edupub/edupub-publication.feature

@@ -51,7 +51,7 @@ Feature: EPUB for Education ▸ Full Publication Checks
 
   ##  4.2 Sectioning
 
-  Scenario: Verify an non-linear content does not have to follow the sectioning rules
+  Scenario: Verify that non-linear content does not have to follow the sectioning rules
     When checking EPUB 'edupub-non-linear-valid'
     Then no errors or warnings are reported
 

src/test/resources/epub-edupub/files/epub/edupub-non-linear-valid/EPUB/nav.xhtml

@@ -8,6 +8,7 @@
 		<nav epub:type="toc">
 			<ol>
 				<li><a href="content_001.xhtml">content 001</a></li>
+				<li><a href="nonlinear.xhtml">non-linear</a></li>
 			</ol>
 		</nav>
 	</body>

src/test/resources/epub-edupub/files/epub/edupub-non-linear-valid/EPUB/package.opf

@@ -11,10 +11,10 @@
 <manifest>
   <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
   <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
-  <item id="non" href="nonlinear.xhtml" media-type="application/xhtml+xml" />
+  <item id="nonlinear" href="nonlinear.xhtml" media-type="application/xhtml+xml" />
 </manifest>
 <spine>
   <itemref idref="content_001" />
-  <itemref idref="non" linear="no" />
+  <itemref idref="nonlinear" linear="no" />
 </spine>
 </package>

src/test/resources/epub-region-nav/files/epub/data-nav-in-spine-warning/EPUB/nav.xhtml

@@ -8,6 +8,7 @@
 		<nav epub:type="toc">
 			<ol>
 				<li><a href="content_001.xhtml">content 001</a></li>
+				<li><a href="data-nav.xhtml">data nav</a></li>
 			</ol>
 		</nav>
 	</body>

src/test/resources/epub3/05-package-document/files/spine-empty-error.opf

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+<!--  <itemref idref="content_001" />-->
+</spine>
+</package>

src/test/resources/epub3/05-package-document/files/spine-no-linear-itemref-error.opf

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" linear=" no "/>
+</spine>
+</package>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-not-reachable-error/EPUB/content_001.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-not-reachable-error/EPUB/content_002.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-not-reachable-error/EPUB/package.opf

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="content_002"  href="content_002.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+  <itemref idref="content_002" linear="no"/>
+</spine>
+</package>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-hyperlink-valid/EPUB/content_001.xhtml

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+		<a href="content_002.xhtml">link</a>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-hyperlink-valid/EPUB/content_002.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-hyperlink-valid/EPUB/package.opf

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="content_002"  href="content_002.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+  <itemref idref="content_002" linear="no"/>
+</spine>
+</package>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-hyperlink-valid/META-INF/container.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
+	<rootfiles>
+		<rootfile full-path="EPUB/package.opf" media-type="application/oebps-package+xml"/>
+	</rootfiles>
+</container>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/EPUB/content_001.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/EPUB/content_002.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/EPUB/nav.xhtml

@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal Nav</title>
+	</head>
+	<body>
+		<nav epub:type="toc">
+			<ol>
+				<li><a href="content_001.xhtml">content 001</a></li>
+				<li><a href="content_002.xhtml">content 002</a></li>
+			</ol>
+		</nav>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/EPUB/package.opf

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="content_002"  href="content_002.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+  <itemref idref="content_002" linear="no"/>
+</spine>
+</package>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/META-INF/container.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
+	<rootfiles>
+		<rootfile full-path="EPUB/package.opf" media-type="application/oebps-package+xml"/>
+	</rootfiles>
+</container>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-nav-valid/mimetype

@@ -0,0 +1 @@
+application/epub+zip

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-script-valid/EPUB/content_001.xhtml

@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<title>Minimal EPUB</title>
+		<script>
+			window.addEventListener("load", function(){
+				var link = document.createElement('a');
+				link.setAttribute('href', 'content_002.xhtml');
+				link.innerHTML = "link";
+				document.body.appendChild(link);
+			});
+		</script>
+	</head>
+	<body id="body">
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-script-valid/EPUB/content_002.xhtml

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-script-valid/EPUB/nav.xhtml

@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal Nav</title>
+	</head>
+	<body>
+		<nav epub:type="toc">
+			<ol>
+				<li><a href="content_001.xhtml">content 001</a></li>
+			</ol>
+		</nav>
+	</body>
+</html>

src/test/resources/epub3/05-package-document/files/spine-nonlinear-reachable-via-script-valid/EPUB/package.opf

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
+  <item id="content_002"  href="content_002.xhtml" media-type="application/xhtml+xml"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+  <itemref idref="content_002" linear="no"/>
+</spine>
+</package>