PY-18816 Acknowledge TypeEvalContext#maySwitchToAST in reference expressions resolve

Don't use getReference().multiResolve() blindly, because now there can
be reference expressions coming from expression fragments and their
presence doesn't mean that surrounding AST has been unstubbed already.

python/src/com/jetbrains/python/codeInsight/regexp/PythonRegexpInjector.java

@@ -30,6 +30,7 @@ import com.jetbrains.python.codeInsight.PyInjectionUtil;
 import com.jetbrains.python.codeInsight.dataflow.scope.ScopeUtil;
 import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.resolve.PyResolveContext;
+import com.jetbrains.python.psi.types.TypeEvalContext;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -89,7 +90,8 @@ public class PythonRegexpInjector implements MultiHostInjector {
 
     if (callee instanceof PyReferenceExpression && canBeRegexpCall(callee)) {
       final PyReferenceExpression referenceExpression = (PyReferenceExpression)callee;
-      return referenceExpression.getReference(PyResolveContext.noImplicits()).resolve();
+      final TypeEvalContext context = TypeEvalContext.codeAnalysis(call.getProject(), call.getContainingFile());
+      return referenceExpression.getReference(PyResolveContext.noImplicits().withTypeEvalContext(context)).resolve();
     }
 
     return null;

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

@@ -285,16 +285,18 @@ public class PyReferenceExpressionImpl extends PyElementImpl implements PyRefere
     final PyResolveContext resolveContext = PyResolveContext.noImplicits().withTypeEvalContext(context);
     final List<PyType> members = new ArrayList<>();
 
-    for (PsiElement target : PyUtil.multiResolveTopPriority(getReference(resolveContext))) {
-      if (target == this || target == null) {
-        continue;
-      }
+    if (context.maySwitchToAST(this)) {
+      for (PsiElement target : PyUtil.multiResolveTopPriority(getReference(resolveContext))) {
+        if (target == this || target == null) {
+          continue;
+        }
 
-      if (!target.isValid()) {
-        throw new PsiInvalidElementAccessException(this);
-      }
+        if (!target.isValid()) {
+          throw new PsiInvalidElementAccessException(this);
+        }
 
-      members.add(getTypeFromTarget(target, context, this));
+        members.add(getTypeFromTarget(target, context, this));
+      }
     }
 
     return PyUnionType.union(members);