some folding

idea/src/META-INF/plugin.xml

@@ -23,6 +23,7 @@
       <lang.parserDefinition language="jet" implementationClass="org.jetbrains.jet.lang.parsing.JetParserDefinition"/>
       <lang.commenter language="jet" implementationClass="org.jetbrains.jet.plugin.JetCommenter"/>
       <lang.psiStructureViewFactory language="jet" implementationClass="org.jetbrains.jet.plugin.structureView.JetStructureViewFactory"/>
+      <lang.foldingBuilder language="jet" implementationClass="org.jetbrains.jet.plugin.JetFoldingBuilder"/>
       <annotator language="jet" implementationClass="org.jetbrains.jet.plugin.annotations.SoftKeywordsAnnotator"/>
       <annotator language="jet" implementationClass="org.jetbrains.jet.plugin.annotations.LabelsAnnotator"/>
       <annotator language="jet" implementationClass="org.jetbrains.jet.plugin.annotations.JetPsiChecker"/>

idea/src/org/jetbrains/jet/plugin/JetFoldingBuilder.java

@@ -0,0 +1,53 @@
+package org.jetbrains.jet.plugin;
+
+import com.intellij.lang.ASTNode;
+import com.intellij.lang.folding.FoldingBuilder;
+import com.intellij.lang.folding.FoldingDescriptor;
+import com.intellij.openapi.editor.Document;
+import com.intellij.openapi.project.DumbAware;
+import com.intellij.openapi.util.TextRange;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.jet.JetNodeTypes;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author yole
+ */
+public class JetFoldingBuilder implements FoldingBuilder, DumbAware {
+    @NotNull
+    @Override
+    public FoldingDescriptor[] buildFoldRegions(@NotNull ASTNode node, @NotNull Document document) {
+        List<FoldingDescriptor> descriptors = new ArrayList<FoldingDescriptor>();
+        appendDescriptors(node, document, descriptors);
+        return descriptors.toArray(new FoldingDescriptor[descriptors.size()]);
+    }
+
+    private void appendDescriptors(ASTNode node, Document document, List<FoldingDescriptor> descriptors) {
+        TextRange textRange = node.getTextRange();
+        if ((node.getElementType() == JetNodeTypes.BLOCK || node.getElementType() == JetNodeTypes.CLASS_BODY) &&
+            !isOneLine(textRange, document)) {
+            descriptors.add(new FoldingDescriptor(node, textRange));
+        }
+        ASTNode child = node.getFirstChildNode();
+        while (child != null) {
+          appendDescriptors(child, document, descriptors);
+          child = child.getTreeNext();
+        }
+    }
+
+    private boolean isOneLine(TextRange textRange, Document document) {
+        return document.getLineNumber(textRange.getStartOffset()) == document.getLineNumber(textRange.getEndOffset());
+    }
+
+    @Override
+    public String getPlaceholderText(@NotNull ASTNode astNode) {
+        return "{...}";
+    }
+
+    @Override
+    public boolean isCollapsedByDefault(@NotNull ASTNode astNode) {
+        return false;
+    }
+}