[clang-format] Improved identification of C# nullables

[jbcoe]

Summary

Allow ? inside C# generics.

Do not mistake casts like (Type?) as conditional operators.

[krasimir]

clang/lib/Format/TokenAnnotator.cpp

1016–1017

nit: add a space before and in the comment:

// ... `Type? name;`and ...

2976

nit: just replace the outer if body by:
return !Right.isOneOf(TT_TemplateCloser, tok::r_paren);

[jbcoe]

Fix nits from review.

[krasimir]

Thank you!

clang/lib/Format/TokenAnnotator.cpp

while (CurrentToken) {
       }
       if (CurrentToken->is(tok::question) &&
           Style.Language == FormatStyle::LK_Java) {
         next();
         continue;
       }
       if (CurrentToken->isOneOf(tok::r_paren, tok::r_square, tok::r_brace) ||
           (CurrentToken->isOneOf(tok::colon, tok::question) && InExprContext &&
-           Style.Language != FormatStyle::LK_Proto &&
+           !Style.isCSharp() && Style.Language != FormatStyle::LK_Proto &&
            Style.Language != FormatStyle::LK_TextProto))
         return false;
       // If a && or || is found and interpreted as a binary operator, this set
       // of angles is likely part of something like "a < b && c > d". If the
       // angles are inside an expression, the ||/&& might also be a binary
       // operator that was misinterpreted because we are parsing template
       // parameters.
       // FIXME: This is getting out of hand, write a decent parser.
case tok::question:
         break;
       }
       // Declarations cannot be conditional expressions, this can only be part
       // of a type declaration.
       if (Line.MustBeDeclaration && !Contexts.back().IsExpression &&
           Style.Language == FormatStyle::LK_JavaScript)
         break;
       if (Style.isCSharp()) {
-        // `Type? name;` and `Type? name =` can only be nullable types.
+        // `Type?)`, `Type?>`, `Type? name;` and `Type? name =` can only be
+        // nullable types.
         // Line.MustBeDeclaration will be true for `Type? name;`.
-        if (!Contexts.back().IsExpression &&
-            (Line.MustBeDeclaration ||
-             (Tok->Next && Tok->Next->is(tok::identifier) && Tok->Next->Next &&
-              Tok->Next->Next->is(tok::equal)))) {
+        if ((!Contexts.back().IsExpression && Line.MustBeDeclaration) ||
+            (Tok->Next && Tok->Next->isOneOf(tok::r_paren, tok::greater)) ||
+             Tok->Next->Next->is(tok::equal))) {
           Tok->Type = TT_CSharpNullable;
           break;
         }
       }
       parseConditional();
       break;
     case tok::kw_template:
       parseTemplateDeclaration();
if (Style.isCpp()) {
     // spaces inside square brackets.
     if (Left.is(tok::l_square) || Right.is(tok::r_square))
       return Style.SpacesInSquareBrackets;
 
     // No space before ? in nullable types.
     if (Right.is(TT_CSharpNullable))
       return false;
 
-    // Require space after ? in nullable types.
+    // Require space after ? in nullable types except in generics and casts.
     if (Left.is(TT_CSharpNullable))
-      return true;
+      return !Right.isOneOf(TT_TemplateCloser, tok::r_paren);
 
     // No space before or after '?.'.
     if (Left.is(TT_CSharpNullConditional) || Right.is(TT_CSharpNullConditional))
       return false;
 
     // Space before and after '??'.
     if (Left.is(TT_CSharpNullCoalescing) || Right.is(TT_CSharpNullCoalescing))
       return true;
 

clang/unittests/Format/FormatTestCSharp.cpp

public class A {
 
   verifyFormat(R"(void foo(int? x, int? y, int? z) {})",
                Style); // Nullables in function definitions.
 
   verifyFormat(R"(public float? Value;)", Style); // no space before `?`.
 
   verifyFormat(R"(int?[] arr = new int?[10];)",
                Style); // An array of a nullable type.
+
+  verifyFormat(R"(var x = (int?)y;)", Style); // Cast to a nullable type.
+
+  verifyFormat(R"(var x = new MyContainer<int?>();)", Style); // Generics.
 }
 
 TEST_F(FormatTestCSharp, CSharpArraySubscripts) {
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
 
   // Do not format array subscript operators as attributes.
   verifyFormat(R"(//
 if (someThings[index].Contains(myThing)) {