fix: Indent async implementation method correctly

python/src/com/jetbrains/python/codeInsight/override/PyOverrideImplementUtil.java

@@ -164,7 +164,16 @@ private static void write(@NotNull PyClass pyClass, @NotNull List<PyMethodMember
     final PyStatementList statementList = cls.getStatementList();
     final TypeEvalContext context = TypeEvalContext.userInitiated(cls.getProject(), cls.getContainingFile());
 
-    final PyFunction function = buildOverriddenFunction(cls, baseFunction, implement).addFunctionAfter(statementList, anchor);
+    final PyFunction function;
+    final PyFunction newFunction = buildOverriddenFunction(cls, baseFunction, implement).buildFunction();
+    if (anchor != null) {
+      function = (PyFunction)statementList.addAfter(newFunction, anchor);
+    }
+    else {
+      // When the statement list is still on the same line as the colon (e.g. the class body is not created yet),
+      // inserting via plain PSI operations may lead to incorrect indentation (especially for nested classes).
+      function = (PyFunction)PyPsiRefactoringUtil.addElementToStatementList(newFunction, statementList, true);
+    }
     PyClassRefactoringUtil.transplantImportsFromSignature(baseFunction, function);
 
     PyiUtil

python/testData/inspections/ImplementAbstractNestedIndentation.py

@@ -0,0 +1,11 @@
+import abc
+
+
+class Abstract(abc.ABC):
+    @abc.abstractmethod
+    async def run(self):
+        pass
+
+
+def test_class():
+    class Conc<caret>rete(Abstract):<EOLError descr="Indent expected"></EOLError>

python/testData/inspections/ImplementAbstractNestedIndentation_after.py

@@ -0,0 +1,13 @@
+import abc
+
+
+class Abstract(abc.ABC):
+    @abc.abstractmethod
+    async def run(self):
+        pass
+
+
+def test_class():
+    class Concrete(Abstract):
+        async def run(self):
+            pass

python/testData/inspections/ImplementAbstractOrder.py

@@ -12,6 +12,10 @@ def foo0(self):
     def foo1(self):
         pass
 
+    @abstractmethod
+    def foo2(self):
+        pass
+
     def bar(self):
         pass
 

python/testData/inspections/ImplementAbstractOrder_after.py

@@ -12,6 +12,10 @@ def foo0(self):
     def foo1(self):
         pass
 
+    @abstractmethod
+    def foo2(self):
+        pass
+
     def bar(self):
         pass
 
@@ -23,3 +27,5 @@ def foo0(self):
     def foo1(self):
         pass
 
+    def foo2(self):
+        pass

python/testSrc/com/jetbrains/python/PyQuickFixTest.kt

@@ -1177,6 +1177,18 @@ class PyQuickFixTest : PyTestCase() {
     )
   }
 
+  fun testImplementAbstractNestedIndentation() {
+    runWithLanguageLevel(LanguageLevel.PYTHON37) {
+      doInspectionTest(
+        "ImplementAbstractNestedIndentation.py",
+        PyAbstractClassInspection::class.java,
+        PyBundle.message("QFIX.NAME.implement.methods"),
+        true,
+        true
+      )
+    }
+  }
+
   fun testRemovingUnderscoresInNumericLiterals() {
     myFixture.configureByText(PythonFileType.INSTANCE, "1_0_0")