PY-16412 Prohibit annotations for structural types

since they cannot be expression in PEP 484 compatible format (yet).

python/src/com/jetbrains/python/PyBundle.properties

@@ -295,6 +295,8 @@ INTN.convert.static.method.to.function=Convert static method to function
 #PyConvertMethodToPropertyIntention
 INTN.convert.method.to.property=Convert method to property
 
+INTN.annotate.variable.type.PEP484.incompatible.type=The type ''{0}'' cannot be expressed in PEP 484 format
+
 # Conflict checker
 CONFLICT.name.$0.obscured=Name ''{0}'' obscured by local definitions
 CONFLICT.name.$0.obscured.cannot.convert=Name ''{0}'' obscured. Cannot convert.

python/src/com/jetbrains/python/codeInsight/intentions/PyAnnotateVariableTypeIntention.java

@@ -2,6 +2,7 @@
 package com.jetbrains.python.codeInsight.intentions;
 
 import com.intellij.codeInsight.TargetElementUtil;
+import com.intellij.codeInsight.hint.HintManager;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.roots.ProjectFileIndex;
@@ -17,6 +18,7 @@ import com.jetbrains.python.codeInsight.controlflow.ScopeOwner;
 import com.jetbrains.python.codeInsight.dataflow.scope.Scope;
 import com.jetbrains.python.codeInsight.dataflow.scope.ScopeUtil;
 import com.jetbrains.python.codeInsight.intentions.PyTypeHintGenerationUtil.AnnotationInfo;
+import com.jetbrains.python.codeInsight.intentions.PyTypeHintGenerationUtil.Pep484IncompatibleTypeException;
 import com.jetbrains.python.documentation.PythonDocumentationProvider;
 import com.jetbrains.python.documentation.doctest.PyDocstringFile;
 import com.jetbrains.python.psi.*;
@@ -192,11 +194,16 @@ public class PyAnnotateVariableTypeIntention extends PyBaseIntentionAction {
     final List<PyTargetExpression> targets = findSuitableTargetsUnderCaret(project, editor, file);
     assert targets.size() == 1;
     final PyTargetExpression annotationTarget = targets.get(0);
-    if (preferSyntacticAnnotation(annotationTarget)) {
-      insertVariableAnnotation(annotationTarget);
+    try {
+      if (preferSyntacticAnnotation(annotationTarget)) {
+        insertVariableAnnotation(annotationTarget);
+      }
+      else {
+        insertVariableTypeComment(annotationTarget);
+      }
     }
-    else {
-      insertVariableTypeComment(annotationTarget);
+    catch (Pep484IncompatibleTypeException e) {
+      HintManager.getInstance().showErrorHint(editor, e.getMessage());
     }
   }
 
@@ -207,6 +214,7 @@ public class PyAnnotateVariableTypeIntention extends PyBaseIntentionAction {
   private static void insertVariableAnnotation(@NotNull PyTargetExpression target) {
     final TypeEvalContext context = TypeEvalContext.userInitiated(target.getProject(), target.getContainingFile());
     final PyType inferredType = context.getType(target);
+    PyTypeHintGenerationUtil.checkPep484Compatibility(inferredType);
     final String annotationText = PythonDocumentationProvider.getTypeName(inferredType, context);
     final AnnotationInfo info = new AnnotationInfo(annotationText, inferredType);
     if (isInstanceAttribute(target, context)) {
@@ -277,6 +285,7 @@ public class PyAnnotateVariableTypeIntention extends PyBaseIntentionAction {
     }
     else if (target instanceof PyTypedElement) {
       final PyType singleTargetType = context.getType((PyTypedElement)target);
+      PyTypeHintGenerationUtil.checkPep484Compatibility(singleTargetType);
       final String singleTargetAnnotation = PythonDocumentationProvider.getTypeName(singleTargetType, context);
       types.add(singleTargetType);
       typeRanges.add(TextRange.from(builder.length(), singleTargetAnnotation.length()));

python/src/com/jetbrains/python/codeInsight/intentions/PyTypeHintGenerationUtil.java

@@ -17,6 +17,7 @@ import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.psi.*;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.util.ThrowableRunnable;
+import com.jetbrains.python.PyBundle;
 import com.jetbrains.python.codeInsight.imports.AddImportHelper;
 import com.jetbrains.python.codeInsight.imports.AddImportHelper.ImportPriority;
 import com.jetbrains.python.codeInsight.typing.PyTypingTypeProvider;
@@ -320,6 +321,38 @@ public class PyTypeHintGenerationUtil {
     }
   }
 
+  public static void checkPep484Compatibility(@Nullable PyType type) {
+    if (type == null ||
+        type instanceof PyNoneType ||
+        type instanceof PyCallableTypeImpl ||
+        type instanceof PyGenericType ||
+        type instanceof PyFunctionType) {
+      return;
+    }
+    else if (type instanceof PyUnionType) {
+      for (PyType memberType : ((PyUnionType)type).getMembers()) {
+        checkPep484Compatibility(memberType);
+      }
+    }
+    else if (type instanceof PyCollectionType) {
+      for (PyType typeParam : ((PyCollectionType)type).getElementTypes()) {
+        checkPep484Compatibility(typeParam);
+      }
+    }
+    else if (type instanceof PyClassType) {
+      // In this order since PyCollectionTypeImpl implements PyClassType
+    }
+    else {
+      throw new Pep484IncompatibleTypeException(PyBundle.message("INTN.annotate.variable.type.PEP484.incompatible.type", type.getName()));
+    }
+  }
+
+  public static final class Pep484IncompatibleTypeException extends RuntimeException {
+    public Pep484IncompatibleTypeException(String message) {
+      super(message);
+    }
+  }
+
   public static final class AnnotationInfo {
     private final String myAnnotationText;
     private final List<PyType> myTypes;

python/testData/intentions/PyAnnotateVariableTypeIntentionTest/annotationNotPossibleForNestedStructuralType.py

@@ -0,0 +1,3 @@
+def func(x):
+    x.foo()
+    va<caret>r = [x]

python/testData/intentions/PyAnnotateVariableTypeIntentionTest/annotationNotPossibleForNestedStructuralType_after.py

@@ -0,0 +1,3 @@
+def func(x):
+    x.foo()
+    var = [x]

python/testData/intentions/PyAnnotateVariableTypeIntentionTest/annotationNotPossibleForStructuralType.py

@@ -0,0 +1,3 @@
+def func(x):
+    x.foo()
+    va<caret>r = x

python/testData/intentions/PyAnnotateVariableTypeIntentionTest/annotationNotPossibleForStructuralType_after.py

@@ -0,0 +1,3 @@
+def func(x):
+    x.foo()
+    var = x

python/testSrc/com/jetbrains/python/intentions/PyAnnotateVariableTypeIntentionTest.java

@@ -215,6 +215,14 @@ public class PyAnnotateVariableTypeIntentionTest extends PyIntentionTestCase {
     doAnnotationTest();
   }
 
+  public void testAnnotationNotPossibleForStructuralType() {
+    doAnnotationTest();
+  }
+
+  public void testAnnotationNotPossibleForNestedStructuralType() {
+    doAnnotationTest();
+  }
+
   private void doAnnotationTest() {
     doTest(LanguageLevel.PYTHON36);
   }