base tag support:

file reference helper for local paths
silence inspections for urls
#WEB-497 fixed

platform/platform-resources/src/META-INF/XmlPlugin.xml

@@ -299,6 +299,7 @@
     <psi.referenceContributor implementation="com.intellij.xml.util.XmlReferenceContributor"/>
     <!--<pom.declarationSearcher implementation="com.intellij.psi.impl.source.resolve.reference.impl.providers.IdDeclarationSearcher"/>-->
     <anchorReferenceProvider implementation="com.intellij.xml.util.AnchorPathReferenceProvider"/>
+    <psi.fileReferenceHelper implementation="com.intellij.codeInsight.daemon.impl.analysis.HtmlFileReferenceHelper"/>
 
     <extendWordSelectionHandler implementation="com.intellij.codeInsight.editorActions.HtmlSelectioner"/>
     <extendWordSelectionHandler implementation="com.intellij.codeInsight.editorActions.XmlTagSelectioner"/>

xml/xml-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/HtmlFileReferenceHelper.java

@@ -0,0 +1,58 @@
+package com.intellij.codeInsight.daemon.impl.analysis;
+
+import com.intellij.ide.highlighter.HtmlFileType;
+import com.intellij.ide.highlighter.XHtmlFileType;
+import com.intellij.openapi.fileTypes.FileType;
+import com.intellij.openapi.module.Module;
+import com.intellij.openapi.module.ModuleUtilCore;
+import com.intellij.openapi.project.Project;
+import com.intellij.openapi.roots.ModuleRootManager;
+import com.intellij.openapi.roots.ProjectRootManager;
+import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.psi.PsiDirectory;
+import com.intellij.psi.PsiFile;
+import com.intellij.psi.PsiFileSystemItem;
+import com.intellij.psi.PsiManager;
+import com.intellij.psi.impl.source.resolve.reference.impl.providers.FileReferenceHelper;
+import com.intellij.psi.xml.XmlFile;
+import com.intellij.xml.util.HtmlUtil;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+
+/**
+ * @author Dennis.Ushakov
+ */
+public class HtmlFileReferenceHelper extends FileReferenceHelper {
+  @NotNull
+  @Override
+  public Collection<PsiFileSystemItem> getContexts(Project project, @NotNull VirtualFile vFile) {
+    final PsiFile file = PsiManager.getInstance(project).findFile(vFile);
+    final Module module = file != null ? ModuleUtilCore.findModuleForPsiElement(file) : null;
+    if (module == null || !(file instanceof XmlFile)) return Collections.emptyList();
+    final String basePath = HtmlUtil.getHrefBase((XmlFile)file);
+    if (basePath != null && !HtmlUtil.hasHtmlPrefix(basePath)) {
+      for (VirtualFile virtualFile : getBaseRoots(module)) {
+        final VirtualFile base = virtualFile.findFileByRelativePath(basePath);
+        final PsiDirectory result = base != null ? PsiManager.getInstance(project).findDirectory(base) : null;
+        if (result != null) {
+          return Collections.<PsiFileSystemItem>singletonList(result);
+        }
+      }
+    }
+    return Collections.emptyList();
+  }
+
+  protected Collection<VirtualFile> getBaseRoots(final Module module) {
+    return Arrays.asList(ModuleRootManager.getInstance(module).getContentRoots());
+  }
+
+  @Override
+  public boolean isMine(Project project, @NotNull VirtualFile file) {
+    final FileType fileType = file.getFileType();
+    return ProjectRootManager.getInstance(project).getFileIndex().isInContent(file) &&
+           fileType == HtmlFileType.INSTANCE || fileType == XHtmlFileType.INSTANCE;
+  }
+}

xml/xml-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/HtmlUnknownAnchorTargetInspection.java

@@ -36,6 +36,6 @@ public class HtmlUnknownAnchorTargetInspection extends XmlPathReferenceInspectio
 
   @Override
   protected boolean needToCheckRef(PsiReference reference) {
-    return reference instanceof AnchorReference;
+    return reference instanceof AnchorReference && HtmlUnknownTargetInspection.notRemoteBase(reference);
   }
 }

xml/xml-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/HtmlUnknownTargetInspection.java

@@ -15,8 +15,11 @@
  */
 package com.intellij.codeInsight.daemon.impl.analysis;
 
+import com.intellij.psi.PsiFile;
 import com.intellij.psi.PsiReference;
+import com.intellij.psi.xml.XmlFile;
 import com.intellij.xml.util.AnchorReference;
+import com.intellij.xml.util.HtmlUtil;
 import org.jetbrains.annotations.NotNull;
 
 /**
@@ -36,6 +39,12 @@ public class HtmlUnknownTargetInspection extends XmlPathReferenceInspection {
 
   @Override
   protected boolean needToCheckRef(PsiReference reference) {
-    return !(reference instanceof AnchorReference);
+    return !(reference instanceof AnchorReference) && notRemoteBase(reference);
+  }
+
+  static boolean notRemoteBase(PsiReference reference) {
+    final PsiFile file = reference.getElement().getContainingFile();
+    final String basePath = file instanceof XmlFile ? HtmlUtil.getHrefBase((XmlFile)file) : null;
+    return basePath == null || !HtmlUtil.hasHtmlPrefix(basePath);
   }
 }

xml/xml-psi-impl/src/com/intellij/xml/util/HtmlUtil.java

@@ -415,6 +415,14 @@ public class HtmlUtil {
     return attributeName.startsWith(HTML5_DATA_ATTR_PREFIX);
   }
 
+  @Nullable
+  public static String getHrefBase(XmlFile file) {
+    final XmlTag root = file.getRootTag();
+    final XmlTag head = root != null ? root.findFirstSubTag("head") : null;
+    final XmlTag base = head != null ? head.findFirstSubTag("base") : null;
+    return base != null ? base.getAttributeValue("href") : null;
+  }
+
   private static class TerminateException extends RuntimeException {
     private static final TerminateException INSTANCE = new TerminateException();
   }