feat: HTML link element resources do not require fallbacks

EPUB 3.3 clarifies the situation of fallbacks for HTML `link` elements.

This commit:
- fully suppresses error CSS-010 that was reported for foreign linked
  stylesheet resources (e.g. XPGT) with no manifest fallbacks
- add a test to verify that other foreign linked resources do not
  require manifest fallbacks

Fix #1247

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

@@ -76,7 +76,7 @@ private void initialize()
     severities.put(MessageId.CSS_007, Severity.INFO);
     severities.put(MessageId.CSS_008, Severity.ERROR);
     severities.put(MessageId.CSS_009, Severity.USAGE);
-    severities.put(MessageId.CSS_010, Severity.ERROR);
+    severities.put(MessageId.CSS_010, Severity.SUPPRESSED);
     severities.put(MessageId.CSS_011, Severity.SUPPRESSED);
     severities.put(MessageId.CSS_012, Severity.USAGE);
     severities.put(MessageId.CSS_013, Severity.USAGE);

src/main/java/com/adobe/epubcheck/ops/OPSHandler.java

@@ -86,8 +86,6 @@ int getColumnNumber()
   protected boolean hasTh = false;
   protected boolean hasThead = false;
   protected boolean hasCaption = false;
-  protected Optional<EPUBLocation> nonStandardStylesheetLink = Optional.absent();
-  protected boolean hasCss = false;
   protected boolean epubTypeInUse = false;
   protected boolean checkedUnsupportedXMLVersion = false;
   protected StringBuilder textNode;
@@ -147,36 +145,6 @@ protected void checkLink(XMLElement e, String attrNS, String attr)
       href = PathUtil.resolveRelativeReference(base, href);
       xrefChecker.get().registerReference(path, parser.getLineNumber(), parser.getColumnNumber(),
           href, XRefChecker.Type.STYLESHEET);
-
-      // Check the mimetype to record possible non-standard stylesheets
-      // with no fallback
-      String mimetype = xrefChecker.get().getMimeType(href);
-      if (mimetype != null)
-      {
-        if (OPFChecker.isBlessedStyleType(mimetype)
-            || OPFChecker.isDeprecatedBlessedStyleType(mimetype))
-        {
-          hasCss = true;
-        }
-        else
-        {
-          nonStandardStylesheetLink = Optional.of(
-              EPUBLocation.create(path, parser.getLineNumber(), parser.getColumnNumber(), href));
-        }
-      }
-    }
-  }
-
-  protected void checkStylesheetFallback()
-  {
-    // stylesheet is considered as having "built-in" fallback if
-    // at least one is found with a blessed CMT (i.e. text/css).
-    // Implem note: xrefChecker is necessarily present if
-    // nonStandardStylesheetLink is present.
-    if (nonStandardStylesheetLink.isPresent() && !hasCss && !xrefChecker.get()
-        .hasValidFallback(nonStandardStylesheetLink.get().getContext().get()).or(false))
-    {
-      report.message(MessageId.CSS_010, nonStandardStylesheetLink.get());
     }
   }
 
@@ -522,10 +490,6 @@ public void endElement()
         }
         textNode = null;
       }
-      else if ("head".equals(name))
-      {
-        checkStylesheetFallback();
-      }
       else if ("table".equals(name))
       {
         if (tableDepth > 0)

src/test/resources/epub3/content-publication.feature

@@ -125,7 +125,10 @@ Feature: EPUB 3 ▸ Content Documents ▸ Full Publication Checks
     Then error RSC-014 is reported
     Then no other errors or warnings are reported
 
-
+  Scenario: Verify a linked resource without a fallback
+    When checking EPUB 'content-xhtml-link-no-fallback-valid'
+    And no errors or warnings are reported
+
   #####  iframes
 
   Scenario: Verify that an `iframe` can reference another XHTML document
@@ -243,8 +246,7 @@ Feature: EPUB 3 ▸ Content Documents ▸ Full Publication Checks
 
   Scenario: Report an xpgt style sheet without a fallback
     See issues #271, #241
-    When checking EPUB 'content-xhtml-xpgt-no-fallback-error'
-    Then error CSS-010 is reported
+    When checking EPUB 'content-xhtml-link-no-fallback-valid'
     And no other errors or warnings are reported
 
 

src/test/resources/epub3/files/epub/package-manifest-css-wrong-media-type-error/EPUB/content_001.xhtml → src/test/resources/epub3/files/epub/content-xhtml-link-no-fallback-valid/EPUB/content_001.xhtml

@@ -3,7 +3,7 @@
 	<head>
 		<meta charset="utf-8"/>
 		<title>Minimal EPUB</title>
-		<link type="text/css" rel="stylesheet" href="style.css" />
+		<link rel="alternate" href="test.txt"/>
 	</head>
 	<body>
 		<h1>Loomings</h1>

src/test/resources/epub3/files/epub/package-manifest-css-wrong-media-type-error/EPUB/package.opf → src/test/resources/epub3/files/epub/content-xhtml-link-no-fallback-valid/EPUB/package.opf

@@ -9,7 +9,7 @@
 <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="css" href="style.css" media-type="xhtml/css" />
+  <item id="text" href="test.txt" media-type="text/plain" />
 </manifest>
 <spine>
   <itemref idref="content_001" />

src/test/resources/epub3/files/epub/content-xhtml-link-no-fallback-valid/EPUB/test.txt

@@ -0,0 +1 @@
+test

src/test/resources/epub3/files/epub/package-manifest-css-wrong-media-type-error/META-INF/container.xml → src/test/resources/epub3/files/epub/content-xhtml-link-no-fallback-valid/META-INF/container.xml

@@ -1,5 +1,5 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<container xmlns="urn:oasis:names:tc:opendocument:xmlns:container" version="1.0">
+<?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>

src/test/resources/epub3/package-publication.feature

@@ -78,11 +78,6 @@ Feature: EPUB 3 ▸ Packages ▸ Full Publication Checks
     Then error RSC-001 is reported 3 times
     And no other errors or warnings are reported
 
-  Scenario: Report a CSS file declared with an invalid media type and no fallback
-    When checking EPUB 'package-manifest-css-wrong-media-type-error'
-    Then error CSS-010 is reported
-    And no errors or warnings are reported
-
 
   ####  3.4.4.3 Manifest Fallbacks