[clang-format] Recognize C# nullable types

[jbcoe]

Summary

Do not confuse C# nullable types with conditional expressions.

Do not put a space before the ? in [access-modifier] Type? variableName;

[jbcoe]

clang/unittests/Format/FormatTestCSharp.cpp

178

This will be formatted as

public Person(string firstName, string lastName, int age = null);

without the Nullable Type.

[krasimir]

clang/unittests/Format/FormatTestCSharp.cpp

609

Could you also try/add a test for an array of nullable type (from language ref docs here) (also an example of using new with a nullable type):

// An array of a nullable type:
int?[] arr = new int?[10];

[jbcoe]

Add additional test following review discussion

clang/lib/Format/FormatToken.h

#define LIST_TOKEN_TYPES                                                       \
   TYPE(TrailingAnnotation)                                                     \
   TYPE(TrailingReturnArrow)                                                    \
   TYPE(TrailingUnaryOperator)                                                  \
   TYPE(TypenameMacro)                                                          \
   TYPE(UnaryOperator)                                                          \
   TYPE(CSharpStringLiteral)                                                    \
   TYPE(CSharpNullCoalescing)                                                   \
   TYPE(CSharpNamedArgumentColon)                                               \
+  TYPE(CSharpNullableTypeQuestionMark)                                         \
   TYPE(Unknown)
 
 enum TokenType {
 #define TYPE(X) TT_##X,
   LIST_TOKEN_TYPES
 #undef TYPE
       NUM_TOKEN_TYPES
 };

clang/lib/Format/TokenAnnotator.cpp

case tok::question:
         Tok->Type = TT_JsTypeOptionalQuestion;
         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() && Line.MustBeDeclaration) {
+        Tok->Type = TT_CSharpNullableTypeQuestionMark;
+        break;
+      }
       parseConditional();
       break;
     case tok::kw_template:
       parseTemplateDeclaration();
       break;
     case tok::comma:
       if (Contexts.back().InCtorInitializer)
         Tok->Type = TT_CtorInitializerComma;
if (Style.isCpp()) {
     // space between type and variable e.g. Dictionary<string,string> foo;
     if (Left.is(TT_TemplateCloser) && Right.is(TT_StartOfName))
       return true;
 
     // space after comma in '[,]'.
     if (Left.is(tok::comma) && Right.is(tok::r_square))
       return Style.SpacesInSquareBrackets;
 
+    // No space before ? in nullable types.
+    if (Right.is(TT_CSharpNullableTypeQuestionMark))
+      return false;
+
     // space between keywords and paren e.g. "using ("
     if (Right.is(tok::l_paren))
       if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when))
         return Style.SpaceBeforeParens == FormatStyle::SBPO_ControlStatements ||
                spaceRequiredBeforeParens(Right);
   } else if (Style.Language == FormatStyle::LK_JavaScript) {
     if (Left.is(TT_JsFatArrow))
       return true;

clang/unittests/Format/FormatTestCSharp.cpp

TEST_F(FormatTestCSharp, CSharpFatArrows) {
   verifyFormat("public override string ToString() => \"{Name}\\{Age}\";");
 }
 
 TEST_F(FormatTestCSharp, CSharpNullConditional) {
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
   Style.SpaceBeforeParens = FormatStyle::SBPO_Always;
 
   verifyFormat(
-      "public Person(string firstName, string lastName, int? age=null)");
+      "public Person(string firstName, string lastName, int? age = null)");
 
   verifyFormat("foo () {\n"
                "  switch (args?.Length) {}\n"
                "}",
                Style);
 
   verifyFormat("switch (args?.Length) {}", Style);
 
TEST_F(FormatTestCSharp, CSharpSpaces) {
   verifyFormat(R"(taskContext.Factory.Run(async () => doThing(args);)", Style);
   verifyFormat(R"(catch (TestException) when (innerFinallyExecuted))", Style);
   verifyFormat(R"(private float[,] Values;)", Style);
 
   Style.SpacesInSquareBrackets = true;
   verifyFormat(R"(private float[, ] Values;)", Style);
 }
 
+TEST_F(FormatTestCSharp, CSharpNullableTypes) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+  Style.SpacesInSquareBrackets = false;
+
+  verifyFormat(R"(public float? Value;)", Style); // no space before `?`.
+
+  // Erroneous spaces in square brackets here will be tackled in a follow-up
+  // patch and are not addressed by setting
+  // `Style.SpacesInSquareBrackets = false;`
+  verifyFormat(R"(int?[] arr = new int?[ 10 ];)",
+               Style); // An array of a nullable type.
+}
+
 } // namespace format
 } // end namespace clang