[clang-format] Correctly handle C# new modifier (#137430)

Fix #75815

Author: owenca

clang/lib/Format/UnwrappedLineParser.cpp

@@ -2089,7 +2089,13 @@ void UnwrappedLineParser::parseStructuralElement(
       parseSquare();
       break;
     case tok::kw_new:
-      parseNew();
+      if (Style.isCSharp() &&
+          (Tokens->peekNextToken()->isAccessSpecifierKeyword() ||
+           (Previous && Previous->isAccessSpecifierKeyword()))) {
+        nextToken();
+      } else {
+        parseNew();
+      }
       break;
     case tok::kw_switch:
       if (Style.isJava())

clang/unittests/Format/FormatTestCSharp.cpp

@@ -689,6 +689,13 @@ TEST_F(FormatTestCSharp, CSharpNewOperator) {
                Style);
 }
 
+TEST_F(FormatTestCSharp, NewModifier) {
+  verifyFormat("public new class NestedC {\n"
+               "  public int x = 100;\n"
+               "}",
+               getLLVMStyle(FormatStyle::LK_CSharp));
+}
+
 TEST_F(FormatTestCSharp, CSharpLambdas) {
   FormatStyle GoogleStyle = getGoogleStyle(FormatStyle::LK_CSharp);
   FormatStyle MicrosoftStyle = getMicrosoftStyle(FormatStyle::LK_CSharp);

clang/unittests/Format/TokenAnnotatorTest.cpp

@@ -3109,6 +3109,17 @@ TEST_F(TokenAnnotatorTest, CSharpGenericTypeConstraint) {
   EXPECT_TOKEN(Tokens[18], tok::r_brace, TT_NamespaceRBrace);
 }
 
+TEST_F(TokenAnnotatorTest, CSharpNewModifier) {
+  auto Tokens = annotate("new public class NestedC {\n"
+                         "  public int x = 100;\n"
+                         "}",
+                         getGoogleStyle(FormatStyle::LK_CSharp));
+  ASSERT_EQ(Tokens.size(), 13u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::identifier, TT_ClassHeadName);
+  EXPECT_TOKEN(Tokens[4], tok::l_brace, TT_ClassLBrace);
+  EXPECT_TOKEN(Tokens[11], tok::r_brace, TT_ClassRBrace);
+}
+
 TEST_F(TokenAnnotatorTest, UnderstandsLabels) {
   auto Tokens = annotate("{ x: break; }");
   ASSERT_EQ(Tokens.size(), 7u) << Tokens;