action to show type of selected expression or expression under caret

idea/src/META-INF/plugin.xml

@@ -14,7 +14,11 @@
   </project-components>
 
   <actions>
-    <!-- Add your actions here -->
+     <action id="ShowJetExpressionType" class="org.jetbrains.jet.plugin.actions.ShowExpressionTypeAction"
+             text="Show Expression Type">
+         <keyboard-shortcut keymap="$default" first-keystroke="control shift Q"/>
+         <add-to-group group-id="CodeMenu" anchor="last"/>
+     </action>
   </actions>
 
   <extensions defaultExtensionNs="com.intellij">

idea/src/org/jetbrains/jet/plugin/actions/ShowExpressionTypeAction.java

+package org.jetbrains.jet.plugin.actions;
+
+import com.intellij.codeInsight.CodeInsightUtilBase;
+import com.intellij.codeInsight.hint.HintManager;
+import com.intellij.openapi.actionSystem.AnAction;
+import com.intellij.openapi.actionSystem.AnActionEvent;
+import com.intellij.openapi.actionSystem.LangDataKeys;
+import com.intellij.openapi.actionSystem.PlatformDataKeys;
+import com.intellij.openapi.editor.Editor;
+import com.intellij.psi.PsiFile;
+import com.intellij.psi.util.PsiTreeUtil;
+import org.jetbrains.jet.lang.psi.JetExpression;
+import org.jetbrains.jet.lang.psi.JetFile;
+import org.jetbrains.jet.lang.resolve.AnalyzingUtils;
+import org.jetbrains.jet.lang.resolve.BindingContext;
+import org.jetbrains.jet.lang.types.JetType;
+import org.jetbrains.jet.plugin.JetLanguage;
+
+/**
+ * @author yole
+ */
+public class ShowExpressionTypeAction extends AnAction {
+    @Override
+    public void actionPerformed(AnActionEvent e) {
+        Editor editor = e.getData(PlatformDataKeys.EDITOR);
+        PsiFile psiFile = e.getData(LangDataKeys.PSI_FILE);
+        assert editor != null && psiFile != null;
+        JetExpression expression;
+        BindingContext bindingContext = AnalyzingUtils.analyzeFileWithCache((JetFile) psiFile);
+        if (editor.getSelectionModel().hasSelection()) {
+            int startOffset = editor.getSelectionModel().getSelectionStart();
+            int endOffset = editor.getSelectionModel().getSelectionEnd();
+            expression = CodeInsightUtilBase.findElementInRange(psiFile, startOffset, endOffset,
+                    JetExpression.class, JetLanguage.INSTANCE);
+        }
+        else {
+            int offset = editor.getCaretModel().getOffset();
+            expression = PsiTreeUtil.getParentOfType(psiFile.findElementAt(offset), JetExpression.class);
+            while (expression != null && bindingContext.getExpressionType(expression) == null) {
+                expression = PsiTreeUtil.getParentOfType(expression, JetExpression.class);
+            }
+            if (expression != null) {
+                editor.getSelectionModel().setSelection(expression.getTextRange().getStartOffset(),
+                        expression.getTextRange().getEndOffset());
+            }
+        }
+        if (expression != null) {
+            JetType type = bindingContext.getExpressionType(expression);
+            if (type != null) {
+                HintManager.getInstance().showInformationHint(editor, type.toString());
+            }
+        }
+    }
+
+    @Override
+    public void update(AnActionEvent e) {
+        Editor editor = e.getData(PlatformDataKeys.EDITOR);
+        PsiFile psiFile = e.getData(LangDataKeys.PSI_FILE);
+        e.getPresentation().setEnabled(editor != null && psiFile instanceof JetFile);
+    }
+}