[clang-format] Fix C# nullable-related errors

This fixes two errors:

Previously, clang-format was splitting up type identifiers from the
nullable ?. This changes this behavior so that the type name sticks with
the operator.

Additionally, nullable operators attached to return types in interface
functions were not parsed correctly. Digging deeper, it looks like
interface bodies were being parsed differently than classes and structs,
causing MustBeDeclaration to be incorrect for interface members. They
now share the same logic.

One other change is reintroducing the CSharpNullable type independent of
JsTypeOptionalQuestion. Despite having a similar semantic purpose, their
actual syntax differs quite a bit.

Reviewed By: MyDeveloperDay, curdeius

Differential Revision: https://reviews.llvm.org/D101860

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/unittests/Format/FormatTestCSharp.cpp b/clang/unittests/Format/FormatTestCSharp.cpp
index 875ff74..427f725 100644
--- a/clang/unittests/Format/FormatTestCSharp.cpp
+++ b/clang/unittests/Format/FormatTestCSharp.cpp
@@ -848,6 +848,21 @@ public class A {
   verifyFormat(R"(var x = (int?)y;)", Style); // Cast to a nullable type.
 
   verifyFormat(R"(var x = new MyContainer<int?>();)", Style); // Generics.
+
+  verifyFormat(R"(//
+public interface I {
+  int? Function();
+})",
+               Style); // Interface methods.
+
+  Style.ColumnLimit = 10;
+  verifyFormat(R"(//
+public VeryLongType? Function(
+    int arg1,
+    int arg2) {
+  //
+})",
+               Style); // ? sticks with identifier.
 }
 
 TEST_F(FormatTestCSharp, CSharpArraySubscripts) {