fixed PY-6766 Compatibility inspection doesn't detect 'raise from'

python/src/com/jetbrains/python/validation/CompatibilityVisitor.java

@@ -250,6 +250,7 @@ public abstract class CompatibilityVisitor extends PyAnnotator {
   @Override
   public void visitPyRaiseStatement(PyRaiseStatement node) {
     super.visitPyRaiseStatement(node);
+    // empty raise
     int len = 0;
     StringBuilder message = new StringBuilder(myCommonMessage);
     for (int i = 0; i != myVersionsToProcess.size(); ++i) {
@@ -261,7 +262,7 @@ public abstract class CompatibilityVisitor extends PyAnnotator {
     }
     commonRegisterProblem(message, " not support this syntax. Raise with no arguments can only be used in an except block",
                           len, node, null);
-
+    // raise 1, 2, 3
     len = 0;
     message = new StringBuilder(myCommonMessage);
     for (int i = 0; i != myVersionsToProcess.size(); ++i) {
@@ -273,6 +274,19 @@ public abstract class CompatibilityVisitor extends PyAnnotator {
     }
     commonRegisterProblem(message, " not support this syntax.",
                           len, node, new ReplaceRaiseStatementQuickFix());
+
+    // raise exception from cause
+    len = 0;
+    message = new StringBuilder(myCommonMessage);
+    for (int i = 0; i != myVersionsToProcess.size(); ++i) {
+      final LanguageLevel languageLevel = myVersionsToProcess.get(i);
+      final boolean hasFrom = UnsupportedFeaturesUtil.raiseHasFromKeyword(node, languageLevel);
+      if (hasFrom) {
+        len = appendLanguageLevel(message, len, languageLevel);
+      }
+    }
+    commonRegisterProblem(message, " not support this syntax.",
+                          len, node, new ReplaceRaiseStatementQuickFix());
   }
 
   @Override

python/src/com/jetbrains/python/validation/UnsupportedFeaturesUtil.java

@@ -4,6 +4,7 @@ import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiWhiteSpace;
 import com.intellij.psi.util.PsiTreeUtil;
+import com.jetbrains.python.PyTokenTypes;
 import com.jetbrains.python.PythonHelpersLocator;
 import com.jetbrains.python.psi.*;
 import org.xml.sax.InputSource;
@@ -91,6 +92,25 @@ public class UnsupportedFeaturesUtil {
     return false;
   }
 
+  public static boolean raiseHasFromKeyword(PyRaiseStatement node, LanguageLevel versionToProcess) {
+    final PyExpression[] expressions = node.getExpressions();
+    if (expressions.length > 0) {
+      if (expressions.length < 2) {
+        return false;
+      }
+      if (!versionToProcess.isPy3K()) {
+        PsiElement element = expressions[0].getNextSibling();
+        while (element instanceof PsiWhiteSpace) {
+          element = element.getNextSibling();
+        }
+        if (element != null && element.getNode().getElementType() == PyTokenTypes.FROM_KEYWORD) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
   public static boolean visitPyListCompExpression(final PyListCompExpression node, LanguageLevel versionToProcess) {
     final List<ComprhForComponent> forComponents = node.getForComponents();
     if (versionToProcess.isPy3K()) {

python/testData/inspections/PyCompatibilityInspection/raiseFrom.py

@@ -0,0 +1,2 @@
+<warning descr="Python version 2.4, 2.5, 2.6, 2.7 do not support this syntax.">raise exception from cause</warning>
+a = 1

python/testSrc/com/jetbrains/python/inspections/PyCompatibilityInspectionTest.java

@@ -64,6 +64,11 @@ public class PyCompatibilityInspectionTest extends PyTestCase {
     doTest();
   }
 
+  public void testRaiseFrom() {
+    setLanguageLevel(LanguageLevel.PYTHON32);
+    doTest();
+  }
+
   public void testReprExpression() {
     doTest();
   }