validate 'assignment to keyword' in Python 3 (PY-1524)

python/src/com/jetbrains/python/PyNames.java

@@ -37,6 +37,7 @@ public class PyNames {
 
   @NonNls public static final String ALL = "__all__";
   @NonNls public static final String SLOTS = "__slots__";
+  @NonNls public static final String DEBUG = "__debug__";
 
   @NonNls private static final Set<String> _UnderscoredAttributes = new HashSet<String>();
   static {

python/src/com/jetbrains/python/psi/PyElementVisitor.java

@@ -237,4 +237,12 @@ public class PyElementVisitor extends PsiElementVisitor {
   public void visitPyAssertStatement(final PyAssertStatement node) {
     visitPyElement(node);
   }
+
+  public void visitPyNoneLiteralExpression(final PyNoneLiteralExpression node) {
+    visitPyElement(node);
+  }
+
+  public void visitPyBoolLiteralExpression(final PyBoolLiteralExpression node) {
+    visitPyElement(node);
+  }
 }

python/src/com/jetbrains/python/psi/impl/PyBoolLiteralExpressionImpl.java

@@ -2,6 +2,7 @@ package com.jetbrains.python.psi.impl;
 
 import com.intellij.lang.ASTNode;
 import com.jetbrains.python.psi.PyBoolLiteralExpression;
+import com.jetbrains.python.psi.PyElementVisitor;
 import com.jetbrains.python.psi.types.PyType;
 import com.jetbrains.python.psi.types.TypeEvalContext;
 import org.jetbrains.annotations.NotNull;
@@ -22,4 +23,9 @@ public class PyBoolLiteralExpressionImpl extends PyElementImpl implements PyBool
   public boolean getValue() {
     return "True".equals(getText());
   }
+
+  @Override
+  protected void acceptPyVisitor(PyElementVisitor pyVisitor) {
+    pyVisitor.visitPyBoolLiteralExpression(this);
+  }
 }

python/src/com/jetbrains/python/psi/impl/PyNoneLiteralExpressionImpl.java

@@ -1,6 +1,7 @@
 package com.jetbrains.python.psi.impl;
 
 import com.intellij.lang.ASTNode;
+import com.jetbrains.python.psi.PyElementVisitor;
 import com.jetbrains.python.psi.PyNoneLiteralExpression;
 import com.jetbrains.python.psi.types.PyNoneType;
 import com.jetbrains.python.psi.types.PyType;
@@ -18,4 +19,9 @@ public class PyNoneLiteralExpressionImpl extends PyElementImpl implements PyNone
   public PyType getType(@NotNull TypeEvalContext context) {
     return PyNoneType.INSTANCE;
   }
+
+  @Override
+  protected void acceptPyVisitor(PyElementVisitor pyVisitor) {
+    pyVisitor.visitPyNoneLiteralExpression(this);
+  }
 }

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

@@ -66,7 +66,7 @@ public class AssignTargetAnnotator extends PyAnnotator {
     @Override
     public void visitPyReferenceExpression(final PyReferenceExpression node) {
       String referencedName = node.getReferencedName();
-      if (referencedName != null && referencedName.equals(PyNames.NONE)) {
+      if (PyNames.NONE.equals(referencedName)) {
         getHolder().createErrorAnnotation(node, (_op == Operation.Delete) ? DELETING_NONE : ASSIGNMENT_TO_NONE);
       }
     }
@@ -74,12 +74,20 @@ public class AssignTargetAnnotator extends PyAnnotator {
     @Override
     public void visitPyTargetExpression(final PyTargetExpression node) {
       String targetName = node.getName();
-      if (targetName != null && targetName.equals(PyNames.NONE)) {
+      if (PyNames.NONE.equals(targetName)) {
         final VirtualFile vfile = node.getContainingFile().getVirtualFile();
         if (vfile != null && !vfile.getUrl().contains("/" + PythonSdkType.SKELETON_DIR_NAME + "/")){
           getHolder().createErrorAnnotation(node, (_op == Operation.Delete) ? DELETING_NONE : ASSIGNMENT_TO_NONE);
         }
       }
+      if (PyNames.DEBUG.equals(targetName)) {
+        if (LanguageLevel.forElement(node).isPy3K()) {
+          getHolder().createErrorAnnotation(node, "assignment to keyword");
+        }
+        else {
+          getHolder().createErrorAnnotation(node, "cannot assign to __debug__");
+        }
+      }
     }
 
     @Override
@@ -182,5 +190,15 @@ public class AssignTargetAnnotator extends PyAnnotator {
     public void visitPyLambdaExpression(final PyLambdaExpression node) {
       getHolder().createErrorAnnotation(node, message("ANN.cant.assign.to.lambda"));
     }
+
+    @Override
+    public void visitPyNoneLiteralExpression(PyNoneLiteralExpression node) {
+      getHolder().createErrorAnnotation(node, "assignment to keyword");
+    }
+
+    @Override
+    public void visitPyBoolLiteralExpression(PyBoolLiteralExpression node) {
+      getHolder().createErrorAnnotation(node, "assignment to keyword");
+    }
   }
 }

python/testData/highlighting/assignmentTargets3K.py

@@ -5,3 +5,7 @@ for a, *b in [(1, 2, 3), (4, 5, 6, 7)]:
 a, b, c = seq[0], seq[1:-1], seq[-1]
 a, *b, c = seq
 [a, *b, c] = seq
+<error descr="assignment to keyword">True</error> = 2
+<error descr="assignment to keyword">False</error> = 1
+<error descr="assignment to keyword">None</error> = 0
+<error descr="assignment to keyword">__debug__</error> = -1