[clang-format] Allow nested [] in C# attributes

[jbcoe]

Summary

Keep track of unpaired [] when identifying C# attribute lines

[krasimir]

That's a bit of a hack (we probably need to hook up full-fledged argument list parsing for complete handling), but this seems like a good trade-off between heuristics and results right now.

clang/lib/Format/UnwrappedLineParser.cpp

void UnwrappedLineParser::parseFile() {
   if (Style.Language == FormatStyle::LK_TextProto &&
       !CommentsBeforeNextToken.empty())
     addUnwrappedLine();
   flushComments(true);
   addUnwrappedLine();
 }
 
 void UnwrappedLineParser::parseCSharpAttribute() {
+  int UnpairedSquareBrackets = 1;
   do {
     switch (FormatTok->Tok.getKind()) {
     case tok::r_square:
       nextToken();
+      --UnpairedSquareBrackets;
+      if (UnpairedSquareBrackets == 0) {
         addUnwrappedLine();
         return;
+      }
+      break;
+    case tok::l_square:
+      ++UnpairedSquareBrackets;
+      nextToken();
+      break;
     default:
       nextToken();
       break;
     }
   } while (!eof());
 }
 
 void UnwrappedLineParser::parseLevel(bool HasOpeningBrace) {

clang/unittests/Format/FormatTestCSharp.cpp

verifyFormat("[SomeAttribute]\n"
                "    int X;\n"
                "}");
 
   // Attributes in a method declaration do not cause line wrapping.
   verifyFormat("void MethodA([In][Out] ref double x)\n"
                "{\n"
                "}");
 
+  // [] in an attribute do not cause premature line wrapping or indenting.
+  verifyFormat(R"(//
+public class A
+{
+    [SomeAttribute(new[] { RED, GREEN, BLUE }, -1.0f, 1.0f)]
+    [DoNotSerialize]
+    public Data MemberVariable;
+})");
+
   //  Unwrappable lines go on a line of their own.
   // 'target:' is not treated as a label.
   // Modify Style to enforce a column limit.
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
   Style.ColumnLimit = 10;
   verifyFormat(R"([assembly:InternalsVisibleTo(
     "SomeAssembly, PublicKey=SomePublicKeyThatExceedsTheColumnLimit")])",
                Style);