PY-21175 Add write instructions for assignments to attributes in CFG

to handle, in particular, lazy initialization scenarios

For instance, the statement "foo.bar = 42" should add a node
"WRITE ACCESS foo.bar" containing the corresponding target expression.

Additionally, "Unused local" inspection doesn't consider writes to
attributes, since, strictly speaking, these are not local names.

python/src/com/jetbrains/python/codeInsight/controlflow/PyControlFlowBuilder.java

@@ -23,6 +23,7 @@ import com.intellij.openapi.util.Ref;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiNamedElement;
 import com.intellij.psi.util.PsiTreeUtil;
+import com.intellij.psi.util.QualifiedName;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.impl.ParamHelper;
@@ -218,19 +219,16 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
 
   @Override
   public void visitPyTargetExpression(final PyTargetExpression node) {
-    final PsiElement[] children = node.getChildren();
-    // Case of non qualified reference
-    if (children.length == 0) {
-      final ReadWriteInstruction.ACCESS access = node.getParent() instanceof PySliceExpression
-                                                 ? ReadWriteInstruction.ACCESS.READ : ReadWriteInstruction.ACCESS.WRITE;
-      final ReadWriteInstruction instruction = ReadWriteInstruction.newInstruction(myBuilder, node, node.getName(), access);
-      myBuilder.addNode(instruction);
-      myBuilder.checkPending(instruction);
-    }
-    else {
-      for (PsiElement child : children) {
-        child.accept(this);
-      }
+    final ReadWriteInstruction.ACCESS access = ReadWriteInstruction.ACCESS.WRITE;
+    final QualifiedName qName = node.asQualifiedName();
+    final String targetName = qName == null ? node.getName() : qName.toString();
+    final ReadWriteInstruction instruction = ReadWriteInstruction.newInstruction(myBuilder, node, targetName, access);
+    myBuilder.addNode(instruction);
+    myBuilder.checkPending(instruction);
+
+    final PyExpression qualifier = node.getQualifier();
+    if (qualifier != null) {
+      qualifier.accept(this);
     }
   }
 

python/src/com/jetbrains/python/inspections/PyUnusedLocalInspectionVisitor.java

@@ -160,6 +160,9 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
         if (name == null || PyNames.UNDERSCORE.equals(name) || scope.isGlobal(name) || scope.isNonlocal(name)) {
           continue;
         }
+        if (element instanceof PyTargetExpression && ((PyTargetExpression)element).isQualified()) {
+          continue;
+        }
         // Ignore underscore-prefixed parameters
         if (name.startsWith(PyNames.UNDERSCORE) && element instanceof PyParameter) {
           continue;

python/src/com/jetbrains/python/refactoring/PyDefUseUtil.java

@@ -96,8 +96,8 @@ public class PyDefUseUtil {
     if (element instanceof PyImportElement) {
       return ((PyImportElement) element).getVisibleName();
     }
-    if (element instanceof PyReferenceExpression) {
-      final QualifiedName qname = ((PyReferenceExpression)element).asQualifiedName();
+    if (element instanceof PyReferenceExpression || element instanceof PyTargetExpression) {
+      final QualifiedName qname = ((PyQualifiedExpression)element).asQualifiedName();
       if (qname != null) {
         return qname.toString();
       }

python/testData/codeInsight/controlflow/qualifiedselfreference.txt

@@ -2,5 +2,6 @@
 1(2) WRITE ACCESS: self
 2(3) WRITE ACCESS: args
 3(4) element: PyAssignmentStatement
-4(5) READ ACCESS: self
-5() element: null
+4(5) WRITE ACCESS: self.args
+5(6) READ ACCESS: self
+6() element: null

python/testData/codeInsight/controlflow/self.txt

@@ -1,7 +1,8 @@
 0(1) element: null
 1(2) WRITE ACCESS: self
 2(3) element: PyAssignmentStatement
-3(4) READ ACCESS: self
-4(5) element: PyPrintStatement
-5(6) READ ACCESS: self
-6() element: null
+3(4) WRITE ACCESS: self.foo
+4(5) READ ACCESS: self
+5(6) element: PyPrintStatement
+6(7) READ ACCESS: self
+7() element: null

python/testSrc/com/jetbrains/python/PyTypeTest.java

@@ -2032,6 +2032,19 @@ public class PyTypeTest extends PyTestCase {
            "expr = x");
   }
 
+  // PY-21175
+  public void testLazyAttributeInitialization() {
+    doTest("int",
+           "class C:\n" +
+           "    def __init__(self):\n" +
+           "        self.attr = None\n" +
+           "    \n" +
+           "    def m(self):\n" +
+           "        if self.attr is None:\n" +
+           "            self.attr = 42\n" +
+           "        expr = self.attr");
+  }
+
   private static List<TypeEvalContext> getTypeEvalContexts(@NotNull PyExpression element) {
     return ImmutableList.of(TypeEvalContext.codeAnalysis(element.getProject(), element.getContainingFile()).withTracing(),
                             TypeEvalContext.userInitiated(element.getProject(), element.getContainingFile()).withTracing());